Dissertations / Theses on the topic 'Quantum Optics and Quantum Information'
To see the other types of publications on this topic, follow the link: Quantum Optics and Quantum Information.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Quantum Optics and Quantum Information.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Pope, Damian. "Contrasting quantum mechanics to local hidden variables theories in quantum optics and quantum information science /." [St. Luica, Qld.], 2002. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16765.pdf.
Full text
2
Michelberger, Patrick Steffen. "Room temperature caesium quantum memory for quantum information applications." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:19c9421d-0276-4c6d-a641-7640d2981da3.
Full textAbstract:
Quantum memories are key components in photonics-based quantum information processing networks. Their ability to store and retrieve information on demand makes repeat-until-success strategies scalable. Warm alkali-metal vapours are interesting candidates for the implementation of such memories, thanks to their very long storage times as well as their experimental simplicity and versatility. Operation with the Raman memory protocol enables high time-bandwidth products, which denote the number of possible storage trials within the memory lifetime. Since large time-bandwidth products enable multiple synchronisation trials of probabilistically operating quantum gates via memory-based temporal multiplexing, the Raman memory is a promising tool for such tasks. Particularly, the broad spectral bandwidth allows for direct and technologically simple interfacing with other photonic primitives, such as heralded single photon sources. Here, this kind of light-matter interface is implemented using a warm caesium vapour Raman memory. Firstly, we study the storage of polarisation-encoded quantum information, a common standard in quantum information processing. High quality polarisation preservation for bright coherent state input signals can be achieved, when operating the Raman memory in a dual-rail configuration inside a polarisation interferometer. Secondly, heralded single photons are stored in the memory. To this end, the memory is operated on-demand by feed-forward of source heralding events, which constitutes a key technological capability for applications in temporal multiplexing. Prior to storage, single photons are produced in a waveguide-based spontaneous parametric down conversion source, whose bespoke design spectrally tailors the heralded photons to the memory acceptance bandwidth. The faithful retrieval of stored single photons is found to be currently limited by noise in the memory, with a signal-to-noise ratio of approximately 0.3 in the memory output. Nevertheless, a clear influence of the quantum nature of an input photon is observed in the retrieved light by measuring the read-out signal's photon statistics via the g(2)-autocorrelation function. Here, we find a drop in g(2) by more than three standard deviations, from g(2) ~ 1.69 to g(2) ~ 1.59 upon changing the input signal from coherent states to heralded single photons. Finally, the memory noise processes and their scalings with the experimental parameters are examined in detail. Four-wave-mixing noise is determined as the sole important noise source for the Raman memory. These experimental results and their theoretical description point towards practical solutions for noise-free operation.
3
Reina, Estupin̄án John-Henry. "Quantum information processing in nanostructures." Thesis, University of Oxford, 2002. http://ora.ox.ac.uk/objects/uuid:6375c7c4-ecf6-4e88-a0f5-ff7493393d37.
Full textAbstract:
Since information has been regarded as a physical entity, the field of quantum information theory has blossomed. This brings novel applications, such as quantum computation. This field has attracted the attention of numerous researchers with backgrounds ranging from computer science, mathematics and engineering, to the physical sciences. Thus, we now have an interdisciplinary field where great efforts are being made in order to build devices that should allow for the processing of information at a quantum level, and also in the understanding of the complex structure of some physical processes at a more basic level. This thesis is devoted to the theoretical study of structures at the nanometer-scale, "nanostructures," through physical processes that mainly involve the solid-state and quantum optics, in order to propose reliable schemes for the processing of quantum information. Initially, the main results of quantum information theory and quantum computation are briefly reviewed. Next, the state-of-the-art of quantum dots technology is described. In so doing, the theoretical background and the practicalities required for this thesis are introduced. A discussion of the current quantum hardware used for quantum information processing is given. In particular, the solid-state proposals to date are emphasised. A detailed prescription is given, using an optically-driven coupled quantum dot system, to reliably prepare and manipulate exciton maximally entangled Bell and Greenberger-Horne-Zeilinger (GHZ) states. Manipulation of the strength and duration of selective light-pulses needed for producing these highly entangled states provides us with crucial elements for the processing of solid-state based quantum information. The all-optical generation of states of the so-called Bell basis for a system of two quantum dots (QDs) is exploited for performing the quantum teleportation of the excitonic state of a dot in an array of three coupled QDs. Theoretical predictions suggest that several hundred single quantum bit rotations and controlled-NOT gates could be performed before decoherence of the excitonic states takes place. In addition, the exciton coherent dynamics of a coupled QD system confined within a semiconductor single mode microcavity is reported. It is shown that this system enables the control of exciton entanglement by varying the coupling strength between the optically-driven dot system and the microcavity. The exciton entanglement shows collapses and revivals for suitable amplitudes of the incident radiation field and dot-cavity coupling strengths. The results given here could offer a new approach for the control of decoherence mechanisms arising from entangled "artificial molecules." In addition to these ultrafast coherent optical control proposals, an approach for reliable implementation of quantum logic gates and long decoherence times in a QD system based on nuclear magnetic resonance (NMR) is given, where the nuclear resonance is controlled by the ground state "magic number" transitions of few-electron QDs in an external magnetic field. The dynamical evolution of quantum registers of arbitrary length in the presence of environmentally-induced decoherence effects is studied in detail. The cases of quantum bits (qubits) coupling individually to different environments ("independent decoherence"), and qubits interacting collectively with the same reservoir ("collective decoherence") are analysed in order to find explicit decoherence functions for any number of qubits. The decay of the coherences of the register is shown to strongly depend on the input states: this sensitivity is a characteristic of both types of coupling (collective and independent) and not only of the collective coupling, as has been reported previously. A non-trivial behaviour - "recoherence" - is found in the decay of the off-diagonal elements of the reduced density matrix in the specific situation of independent decoherence. The results lead to the identification of decoherence-free states in the collective decoherence limit. These states belong to subspaces of the system's Hilbert space that do not become entangled with the environment, making them ideal elements for the engineering of "noiseless" quantum codes. The relations between decoherence of the quantum register and computational complexity based on the new dynamical results obtained for the register density matrix are also discussed. This thesis concludes by summarising and pointing out future directions, and in particular, by discussing some biological resonant energy transfer processes that may be useful for the processing of information at a quantum level.
4
Hessmo, Björn. "Quantum optics in constrained geometries." Doctoral thesis, Uppsala University, Department of Quantum Chemistry, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1208.
Full textAbstract:
When light exhibits particle properties, and when matter exhibits wave properties quantum mechanics is needed to describe physical phenomena.
A two-photon source produces nonmaximally entangled photon pairs when the source is small enough to diffract light. It is shown that diffraction degrades the entanglement. Quantum states produced in this way are used to probe the complementarity between path information and interference in Young's double slit experiment.
When two photons have a nonmaximally entangled polarization it is shown that the Pancharatnam phase is dependent on the entanglement in a nontrivial way. This could be used for implementing simple quantum logical circuits.
Magnetic traps are capable of holding cold neutral atoms. It is shown that magnetic traps and guides can be generated by thin wires etched on a surface using standard nanofabrication technology. These atom chips can hold and manipulate atoms located a few microns above the surface with very high accuracy. The potentials are very versatile and allows for highly complex designs, one such design implemented here is a beam splitter for neutral atoms. Interferometry with these confined de Broglie is also considered. These atom chips could be used for implementing quantum logical circuits.
5
Devitt, Simon John. "Quantum information engineering : concepts to quantum technologies /." Connect to thesis, 2007. http://eprints.unimelb.edu.au/archive/00003925.
Full text
6
Kaiser, Florian. "Photonic entanglement engineering for quantum information applications and fundamental quantum optics." Nice, 2012. https://tel.archives-ouvertes.fr/tel-00777002.
Full textAbstract:
Le but de cette thèse est de développer des sources d’intrication photonique pour étudier les réseaux de communication quantique et l’optique quantique fondamentale. Trois sources très performantes sont construites uniquement autour de composants standards de l’optique intégrée et des télécommunications optiques. La première source génère de l’intrication en polarisation via une séparation déterministe des paires de photons dans deux canaux adjacents des télécommunications. Cette source est donc naturellement adaptée à la cryptographie quantique dans les réseaux à multiplexage en longueurs d’ondes. La seconde source génère, pour la première fois, de l’intrication en time-bins croisés, autorisant l'implémentation de crypto-systèmes quantiques à base d’analyseurs passifs uniquement. La troisième source génère, avec une efficacité record, de l’intrication en polarisation via un convertisseur d’observable temps/polarisation. La bande spectrale des photons peut être choisie sur plus de cinq ordres de grandeur (25 MHz - 4 THz), rendant la source compatible avec toute une variété d’applications avancées, telles que la cryptographie, les relais et les mémoires quantiques. Par ailleurs, cette source est utilisée pour revisiter la notion de Bohr sur la complémentarité des photons uniques en employant un interféromètre de Mach-Zehnder dont la lame séparatrice de sortie se trouve dans une superposition quantique d’être à la fois présente et absente. Enfin, pour adapter la longueur d’onde des paires des photons télécoms intriqués vers les longueurs d’ondes d’absorption des mémoires quantiques actuelles, un convertisseur cohérent de longueur d’onde est présenté et discutéThe aim of this thesis is to develop sources of photonic entanglement to study both quantum networking tasks and some of the foundations of quantum physics. To this end, three high-performance sources are developed, each of them taking extensively advantage of standard telecom fibre optics components. The first source generates polarization entanglement via deterministic pair separation in two adjacent telecommunication channels. This source is naturally suitable for quantum cryptography in wavelength multiplexed network structures. The second source generates for the first time a cross time-bin entangled bi-photon state which allows for quantum key distribution tasks using only passive analyzers. The third source generates, with a record efficiency, polarization entanglement using an energy-time to polarization entanglement transcriber. The photon spectral bandwidth can be chosen over more than five orders of magnitude (25 MHz - 4 THz). This permits implementing the source into existing telecom networks, but also in advanced quantum relay and quantum memory applications. Moreover, this source is used to revisit Bohr’s single-photon wave-particle complementarity notion via employing a Mach-Zehnder interferometer with an output quantum beam-splitter in a true superposition of being present and absent. Finally, to adapt the wavelength of the entangled telecom photon pairs to the absorption wavelength of current quantum memories, a coherent wavelength converter is presented and discussed
7
McKeever, Jason Terence Taylor Kimble H. Jeff. "Trapped atoms in cavity QED for quantum optics and quantum information /." Diss., Pasadena, Calif. : California Institute of Technology, 2004. http://resolver.caltech.edu/CaltechETD:etd-06032004-163753.
Full text
8
Loock, Peter van. "Quantum communication with continuous variables." Thesis, Bangor University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368766.
Full text
9
Zhang, Zheshen. "New techniques for quantum communication systems." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42843.
Full textAbstract:
Although mathematical cryptography has been widely used, its security has only been proven under certain assumptions such as the computational power of opponents. As an alternative, quantum communication, in particular quantum key distribution (QKD) can get around unproven assumptions and achieve unconditional security. However, the key generation rate of practical QKD systems is limited by device imperfections, excess noise from the quantum channel, limited rate of true random-number generation, quantum entanglement preparation, and/or post-processing efficiency. This dissertation contributes to improving the performance of quantum communication systems. First, it proposes a new continuous-variable QKD (CVQKD) protocol that loosens the efficiency requirement on post-processing, a bottleneck for long-distance CVQKD systems. It also demonstrates an experimental implementation of the proposed protocol. To achieve high rates, the CVQKD experiment uses a continuous-wave local oscillator (CWLO). The excess noise caused by guided acoustic-wave Brillioun scattering (GAWBS) is avoided by a frequency-shift scheme, resulting in a 32 dB noise reduction. The statistical distribution of the GAWBS noise is characterized by quantum tomography. Measurements show Gaussian statistics upto 55 dB of dynamical range, which validates the security calculations in the proposed CVQKD protocol. True random numbers are required in quantum and classical cryptography. A second contribution of this thesis is that it experimentally demonstrates an ultrafast quantum random-number generator (QRNG) based on amplified spontaneous emission (ASE). Random numbers are produced by a multi-mode photon counting measurement on ASE light. The performance of the QRNG is analyzed with quantum information theory and verified with NIST standard random-number test. The QRNG experiment demonstrates a random-number generation rate at 20 Gbits/s. Theoretical studies show fundamental limits for such QRNGs. Quantum entanglement produced in nonlinear optical processes can help to increase quantum communication distance. A third contribution is the research on nonlinear optics of graphene, a novel 2D material with unconventional physical properties. Based on a quantum-dynamical model, optical responses of graphene are derived, showing for the first time a link between the complex linear optical conductivity and the quantum decoherence. Nonlinear optical responses, in particular four-wave mixing, is studied for the first time. The theory predicts saturation effects in graphene and relates the saturation threshold to the ultrafast quantum decoherence and carrier relaxation in graphene. For the experimental part, four-wave mixing in graphene is demonstrated. Twin-photon production in graphene is under investigation.
10
Jenkins, Stewart David. "Theory of light -atomic ensemble interactions entanglement, storage, and retrieval /." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-09252006-175848/.
Full textAbstract:
Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2007.Kennedy, T. A. Brian, Committee Chair ; Kuzmich, Alex, Committee Member ; Chapman, Michael S., Committee Member ; Raman, Chandra, Committee Member ; Morley, Thomas D., Committee Member.
11
Humphreys, Peter Conway. "Experimental and theoretical techniques for quantum-enhanced metrology and optical quantum information processing." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:57e942ac-f6f1-43fe-ac77-ef85b7db85ca.
Full textAbstract:
Over the last few decades, quantised excitations of the electromagnetic field have proven to be an ideal system with which to investigate and harness quantum optical phenomena. The techniques developed have enabled fundamental tests of quantum mechanics as well as practical applications in quantum metrology and quantum information processing. Advancing to larger-scale entangled quantum systems will open up new regimes of quantum many-body physics, allowing us to probe the limits of quantum mechanics and enabling truly quantum-enhanced technologies. However, moving towards this goal will require further experimental and theoretical innovations. The work described in this thesis focuses on several different aspects of optical quantum information, but are ultimately all linked by this long-term aim. The first part of this thesis describes a novel method for strain-based active control of quantum optical circuits and a new method for the characterisation of high efficiency detectors. Building on this, I discuss in detail two different fields of quantum optics that stand to benefit from these techniques. I initially consider quantum-enhanced metrology, including work aimed towards demonstrating a truly better-than-classical phase measurement, and a theoretical exploration of multiple-phase estimation. Finally, I focus on linear-optical quantum information processing, exploring in detail the use of time-frequency encodings for quantum computing.
12
Le, Jeannic Hanna. "Optical Hybrid Quantum Information processing." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066596/document.
Full textAbstract:
Approche hybride du traitement quantique de l'information La dualité onde-particule a conduit à deux façons d'encoder l'information quantique, les approches continues et discrètes. L'approche hybride a récemment émergé, et consiste à utiliser les concepts et boites à outils des deux approches, afin de venir à bout des limitations intrinsèques à chaque champ. Dans ce travail de thèse, nous allons dans une première partie utiliser des protocoles hybrides de façon à générer des états quantiques non-gaussiens de la lumière. A l'aide d'oscillateurs paramétriques optiques, et de détecteur de photons supraconducteurs, nous pouvons générer des photons uniques extrêmement purs très efficacement, ainsi que des états chats de Schrödinger, qui permettent d'encoder l'information en variables continues. Nous montrons également en quoi des opérations de variables continues peuvent aider cette génération. La méthode utilisée, basée sur la génération " d'états-noyaux " rend en outre ces états plus robustes à la décohérence. Dans une seconde partie, dans le contexte d'un réseau hétérogène, basé sur différents encodages, relier de façon quantique les deux mondes, nécessite l'existence d'intrication hybride de la lumière. Nous introduisons la notion d'intrication hybride, entre des états continus et discrets, et nous en montrons une première application qui est la génération à distance de bit quantique continu. Nous implémentons ainsi également une plateforme polyvalente permettant la génération d'états " micro-macro " intriquésIn quantum information science and technology, two traditionally-separated ways of encoding information coexist -the continuous and the discrete approaches, resulting from the wave-particle duality of light. The first one is based on quadrature components, while the second one involves single photons. The recent optical hybrid approach aims at using both discrete and continuous concepts and toolboxes to overcome the intrinsic limitations of each field. In this PhD work, first, we use hybrid protocols in order to realize the quantum state engineering of various non-Gaussian states of light. Based on optical parametric oscillators and highly-efficient superconducting-nanowire single-photon detectors, we demonstrate the realization of a high-brightness single-photon source and the quantum state engineering of large optical Schrödinger cat states, which can be used as a continuous-variable qubit. We show how continuous-variable operations such as squeezing can help in this generation. This method based on so-called core states also enables to generate cat states that are more robust to decoherence. Second, in the context of heterogeneous networks based on both encodings, bridging the two worlds by a quantum link requires hybrid entanglement of light. We introduce optical hybrid entanglement between qubits and qutrits of continuous and discrete types, and demonstrate as a first application the remote state preparation of continuous-variable qubits. Our experiment is also a versatile platform to study squeezing-induced micro-macro entanglement
13
Chaudhury, Souma. "Quantum Control and Quantum Chaos in Atomic Spin Systems." Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/195449.
Full textAbstract:
Laser-cooled atoms offer an excellent platform for testing new ideas of quantum control and measurement. I will discuss experiments where we use light and magnetic fields to drive and monitor non-trivial quantum dynamics of a large spin-angular momentum associated with an atomic hyperfine ground state. We can design Hamiltonians to generate arbitrary spin states and perform a full quantum state reconstruction of the results. We have implemented and verified time optimal controls to generate a broad variety of spin states, including spin-squeezed states useful for metrology. Yields achieved are of the range 0.8-0.9.We present a first experimental demonstration of the quantum kicked top, a popular paradigm for quantum and classical chaos. We make `movies' of the evolving quantum state which provides a direct observation of phase space dynamics of this system. The spin dynamics seen in the experiment includes dynamical tunneling between regular islands, rapid spreading of states throughout the chaotic sea, and surprisingly robust signatures of classical phase space structures. Our data show differences between regular and chaotic dynamics in the sensitivity to perturbations of the quantum kicked top Hamiltonian and in the average electron-nuclear spin entanglement during the first 40 kicks. The difference, while clear, is modest due to the small size of the spin.
14
Maurer, Peter. "Coherent control of diamond defects for quantum information science and quantum sensing." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11431.
Full textAbstract:
Quantum mechanics, arguably one of the greatest achievements of modern physics, has not only fundamentally changed our understanding of nature but is also taking an ever increasing role in engineering. Today, the control of quantum systems has already had a far-reaching impact on time and frequency metrology. By gaining further control over a large variety of different quantum systems, many potential applications are emerging. Those applications range from the development of quantum sensors and new quantum metrological approaches to the realization of quantum information processors and quantum networks. Unfortunately most quantum systems are very fragile objects that require tremendous experimental effort to avoid dephasing. Being able to control the interaction between a quantum system with its local environment embodies therefore an important aspect for application and hence is at the focus of this thesis.Physics
15
Oza, Neal N. "Engineering Photonic Switches for Quantum Information Processing." Thesis, Northwestern University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3669298.
Full textAbstract:
In this dissertation, we describe, characterize, and demonstrate the operation of a dual-in, dual-out, all-optical, fiber-based quantum switch. This "cross-bar" switch is particularly useful for applications in quantum information processing because of its low-loss, high-speed, low-noise, and quantum-state-retention properties.
Building upon on our lab's prior development of an ultrafast demultiplexer [1-3] , the new cross-bar switch can be used as a tunable multiplexer and demultiplexer. In addition to this more functional geometry, we present results demonstrating faster performance with a switching window of ≈45 ps, corresponding to >20-GHz switching rates. We show a switching fidelity of >98%, i. e., switched polarization-encoded photonic qubits are virtually identical to unswitched photonic qubits. We also demonstrate the ability to select one channel from a two-channel quantum data stream with the state of the measured (recovered) quantum channel having >96% relative fidelity with the state of that channel transmitted alone. We separate the two channels of the quantum data stream by 155 ps, corresponding to a 6.5-GHz datastream.
Finally, we describe, develop, and demonstrate an application that utilizes the switch's higher-speed, lower-loss, and spatio-temporal-encoding features to perform quantum state tomographies on entangled states in higher-dimensional Hilbert spaces. Since many previous demonstrations show bipartite entanglement of two-level systems, we define "higher" as d > 2 where d represents the dimensionality of a photon. We show that we can generate and measure time-bin-entangled, two-photon, qutrit (d = 3) and ququat (d = 4) states with >85% and >64% fidelity to an ideal maximally entangled state, respectively. Such higher-dimensional states have applications in dense coding [4] , loophole-free tests of nonlocality [5] , simplifying quantum logic gates [6] , and increasing tolerance to noise and loss for quantum information processing [7] .
16
Menzies, David. "Procrustean entanglement concentration, weak measurements and optimized state preparation for continuous-variable quantum optics." Thesis, St Andrews, 2009. http://hdl.handle.net/10023/739.
Full text
17
Kok, Pieter. "State preparation and some applications in quantum optics within the context of quantum information theory." Thesis, Bangor University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327425.
Full text
18
Rådmark, Magnus. "Photonic quantum information and experimental tests of foundations of quantum mechanics." Doctoral thesis, Stockholms universitet, Fysikum, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-37464.
Full textAbstract:
Entanglement is a key resource in many quantum information schemes and in the last years the research on multi-qubit entanglement has drawn lots of attention. In this thesis the experimental generation and characterisation of multi-qubit entanglement is presented. Specifically we have prepared entangled states of up to six qubits. The qubits were implemented in the polarisation degree of freedom of single photons. We emphasise that one type of states that we produce are rotationally invariant states, remaining unchanged under simultaneous identical unitary transformations of all their individual constituents. Such states can be applied to e.g. decoherence-free encoding, quantum communication without sharing a common reference frame, quantum telecloning, secret sharing and remote state preparation schemes. They also have properties which are interesting in studies of foundations of quantum mechanics. In the experimental implementation we use a single source of entangled photon pairs, based on parametric down-conversion, and extract the first, second and third order events. Our experimental setup is completely free from interferometric overlaps, making it robust and contributing to a high fidelity of the generated states. To our knowledge, the achieved fidelity is the highest that has been observed for six-qubit entangled states and our measurement results are in very good agreement with predictions of quantum theory. We have also performed another novel test of the foundations of quantum mechanics. It is based on an inequality that is fulfilled by any non-contextual hidden variable theory, but can be violated by quantum mechanics. This test is similar to Bell inequality tests, which rule out local hidden variable theories as possible completions of quantum mechanics. Here, however, we show that non-contextual hidden variable theories cannot explain certain experimental results, which are consistent with quantum mechanics. Hence, neither of these theories can be used to make quantum mechanics complete.
19
Sansavini, Francesca. "Quantum information protocols in complex entangled networks." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18512/.
Full textAbstract:
Quantum entangled networks represent essential tools for Quantum Communication, i.e. the exchange of Quantum Information between parties. This work consists in the theoretical study of continuous variables (CV) entangled networks - which can be deterministically generated via multimode squeezed light - with complex topology. In particular we investigate CV complex quantum networks properties for quantum communication protocols. We focused on the role played by the topology in the implementation and the optimization of given characteristics of our entangled resource that are useful for a specific quantum communication task, i.e. the creation of an entanglement link between two arbitrary nodes of the resource we are provided with. We implemented an analytical procedure for the generation of entangled complex networks, their optimization and their manipulation via global linear optics operations. We also developed a numerical procedure, based on an evolutionary algorithm, for manipulating entanglement connections via local linear optics operations. Finally, we analyzed the re-shaping of our entangled resource via homodyne measurements.
20
Metcalf, Benjamin James. "Silica-on-silicon waveguide circuits and superconducting detectors for integrated quantum information processing." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:8b5482f6-93a7-4d6e-b335-ba258ad3de1e.
Full textAbstract:
Building complex quantum systems has the potential to reveal phenomena that cannot be studied using classical simulation. Photonics has proven to be an effective test-bed for the investigation of such quantum-enhanced technologies, however, the proliferation of bulk optical components is unlikely to be a scalable route towards building more complex devices. Instead, the miniaturisation, inherent phase stability and trivial alignment afforded by integrated photonic systems has been shown to be a promising alternative. In the first half of this thesis, we describe experiments exploiting the quantum interference of three single photons on a reconfigurable integrated photonic chip. We develop a low-loss source of single photons and introduce a low-loss silica-on-silicon waveguide architecture which enables us to show the first genuine quantum interference of three single photons on an integrated platform. A loss-tolerant, element-wise characterisation scheme is developed along with a statistical test to verify that this multi-photon circuit behaves as expected. We then make use of this three-photon interference to detail the first proof-of-principle demonstration of a new intermediate model of quantum computation called boson sampling. Finally, we perform an on-chip demonstration of the quantum teleportation protocol where all key parts --- entanglement preparation, Bell-state analysis and quantum state tomography --- are performed on a reconfigurable photonic chip. The element-wise characterisation scheme developed earlier is shown to be critical to mitigate fabricated component errors. We develop a theoretical model to account for all sources of possible error in the circuit and find good agreement with the measured teleported state fidelities, which exceed the average teleportation fidelity possible with a classical device. We identify the elements of this error budget relevant to scaling and propose improvements to chip characterisation and fabrication in order to achieve high fidelity operation. In the second half, we discuss the use of high efficiency superconducting transition edge sensors in enabling quantum experiments using more photons. We detail the installation and characterisation of these detectors in a new lab in Oxford. We achieve good photon number-resolution and high-efficiency operation. Work to integrate these detectors on the silica-on-silicon waveguide architecture is discussed and we detail the optical and thermal device modelling performed to optimise the on-chip detection efficiency. New, on-chip detectors, fabricated according to this design are shown to operate as expected and achieve high-efficiency and good energy resolution.
21
Croal, Callum. "Quantum correlations in continuous variable mixed states : from discord to signatures." Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/8969.
Full textAbstract:
This thesis studies continuous variable mixed states with the aim of better understanding the fundamental behaviour of quantum correlations in such states, as well as searching for applications of these correlations. I first investigate the interesting phenomenon of discord increase under local loss and explain the behaviour by considering the non-orthogonality of quantum states. I then explore the counter-intuitive result where entanglement can be created by a passive optical beamsplitter, even if the input states are classical, as long as the input states are part of a larger globally nonclassical system. This result emphasises the importance of global correlations in a quantum state, and I propose an application of this protocol in the form of quantum dense coding. Finally, I develop a quantum digital signature protocol that can be described entirely using the continuous variable formalism. Quantum digital signatures provide a method to ensure the integrity and provenance of a message using quantum states. They follow a similar method to quantum key distribution (QKD), but require less post-processing, which means they can sometimes be implemented over channels that are inappropriate for QKD. The method I propose uses homodyne measurement to verify the signature, unlike previous protocols that use single photon detection. The single photon detection of previous methods is designed to give unambiguous results about the signature, but this comes at the cost of getting no information much of the time. Using homodyne detection has the advantage of giving results all the time, but this means that measurement results always have some ambiguity. I show that, even with this ambiguity, the signature protocol based on homodyne measurement outperforms previous protocols, with the advantage enhanced when technical considerations are included. Therefore this represents an interesting new direction in the search for a practical quantum digital signature scheme.
22
Matthews, Jonathan C. F. "Multi-photon quantum information science and technology in integrated optics." Thesis, University of Bristol, 2011. http://hdl.handle.net/1983/9199e590-ef8b-4a6f-b032-507b0960adc4.
Full textAbstract:
Fundamental quantum physics and quantum information science has found great experimental success with the implementation of single photons. To date, however, the majority of quantum optical experiments use large scale (bulk) optical elements bolted down to an optical bench; an approach that ultimately limits the complexity and stability of quantum circuits required for quantum science and technology (QST). Here, a series of experiments are reported in the emerging field of integrated quantum photonics that show monolithic waveguide chips to be a suitable platform for realising the next generation of quantum optical circuits. The thesis begins by reporting high quality Hong-Ou-Mandel interference-a phenomena that is central to nearly all photonic QST -in directly written waveguide structures. We then observe multi-photon quantum interference in lithographically fabricated waveguide circuits to implement the following demonstrations relevant to quantum computation, quantum metrology and analogue quantum simulation: (i) a compiled version of Shor's quantum algorithm is performed to factorize 15, using a number of integrated single- and two-qubit gates; (ii) a reconfigurable circuit is used to observe super-sensitive quantum interference fringes by manipulating two- and four-photon number-path entanglement; (iii) high quality quantum interference is observed in the reconfigurable device, indicating use as a building block for arbitrary reconfigurable circuits and (iv) a scheme for heralding two- and four-photon entanglement is implemented using projective measurement of auxiliary photons. The capabilities of integrated quantum photonics are extended beyond those of bulk quantum optics with two further demonstrations using arrays of evanescently coupled waveguide: (v) continuous quantum interference of two photons in a 21 mode quantum walk is realised, demonstrating generalisation of the Hong-OuMandel effect and (vi) the symmetry and quantum correlations of two polarisation entangled photons injected into a waveguide array are used to directly simulate quantum interference of fermions, bosons and a continuum of fractional behaviour exhibited by anyons. The latter demonstration is shown to generalise simulation of quantum interference in any mode transformation and to simulate quantum interference of any number of particles. For both demonstrations, implementing such unitary evolution with bulk optics would require hundreds of individual elements in a large interferometric structure which in practice is beyond the abilities of conventional quantum optics. The results presented in this thesis report elementary integrated circuits for future quantum devices and presents quantum experiments realised in integrated photonics, that cannot be realised with bulk optical components. These demonstrations are foundational in developing a new quantum photonic platform necessary for studying fundamental quantum physics and for advancing quantum information science and technology.
23
Cooper, Merlin Frederick Wilmot. "Measurement and manipulation of quantum states of travelling light fields." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:79164748-ebb3-48e2-b4d4-1a4766d29217.
Full textAbstract:
This thesis is concerned with the generation of non-classical quantum states of light, the photon-level manipulation of quantum states and the accurate tomography of both quantum states and quantum processes. In optics, quantum information can be encoded and processed in both discrete and continuous variables. Hybrid approaches combining for example homodyne detection with conditional state preparation and manipulation are gaining increasing prominence. The development and characterization of a time-domain balanced homodyne detector (BHD) is presented. The detector has a bandwidth of 80 MHz, a signal-to-noise ratio of 14.5 dB and an efficiency of 86% making it well-suited to pulse-to-pulse measurement of quantum optical states. The BHD is employed to perform quantum state tomography (QST) of non-classical multi-photon Fock states generated by spontaneous parametric down-conversion. A detailed investigation of the mode-matching between the local oscillator used for homodyne detection and the generated Fock states is presented. The one-, two- and three-photon Fock states are reconstructed with a combined preparation and detection efficiency exceeding 50%. Fock states have a number of applications in quantum state engineering, where non-classical ancilla states and conditional measurements enable photon-level manipulation of quantum states. Fock state filtration (FSF) is investigated - an example of a post-selected beam splitter which is a basic building block for many quantum state engineering protocols. A model is developed incorporating the effect of experimental imperfections. An experimental implementation of a Fock state filter is fully characterized by means of coherent-state quantum process tomography (QPT). The reconstructed process is found to be consistent with the model. The filter preferentially removes the single-photon component from an arbitrary input quantum state. Calibration of optical detectors in the quantum regime is discussed. Quantum detector tomography (QDT) is reviewed and contrasted with a new technique for performing QST with a calibrated detector known as the fitting of data patterns (FDP). The first experimental characterization of a BHD is performed by probing the detector with phase-averaged coherent states. The FDP method is shown to be applicable to the estimation of quantum processes, where a detector response is not assumed - thus demonstrating the versatility of the FDP approach as a new method in the quantum tomography toolbox.
24
Schafer, Joachim. "Information transmission through bosonic gaussian channels." Doctoral thesis, Universite Libre de Bruxelles, 2013. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209420.
Full textAbstract:
In this thesis we study the information transmission through Gaussian quantum channels. Gaussian quantum channels model physical communication links, such as free space communication or optical fibers and therefore, may be considered as the most relevant quantum channels. One of the central characteristics of any communication channel is its capacity. In this work we are interested in the classical capacity, which is the maximal number of bits that can be reliably transmitted per channel use. An important lower bound on the classical capacity is given by the Gaussian capacity, which is the maximal transmission rate with the restriction that only Gaussian encodings are allowed: input messages are encoded in so-called Gaussian states for which the mean field amplitudes are Gaussian distributed.We focus in this work mainly on the Gaussian capacity for the following reasons. First, Gaussian encodings are easily accessible experimentally. Second, the difficulty of studying the classical capacity, which arises due to an optimization problem in an infinite dimensional Hilbert space, is greatly reduced when considering only Gaussian input encodings. Third, the Gaussian capacity is conjectured to coincide with the classical capacity, even though this longstanding conjecture is unsolved until today.
We start with the investigation of the capacities of the single-mode Gaussian channel. We show that the most general case can be reduced to a simple, fiducial Gaussian channel which depends only on three parameters: its transmissivity (or gain), the added noise variance and the squeezing of the noise. Above a certain input energy threshold, the optimal input variances are given by a quantum water-filling solution, which implies that the optimal modulated output state is a thermal state. This is a quantum extension (or generalization) of the well-known classical water-filling solution for parallel Gaussian channels. Below the energy threshold the solution is given by a transcendental equation and only the less noisy quadrature is modulated. We characterize in detail the dependence of the Gaussian capacity on its channel parameters. In particular, we show that the Gaussian capacity is a non-monotonous function of the noise squeezing and analytically specify the regions where it exhibits one maximum, a maximum and a minimum, a saddle point or no extrema.
Then, we investigate the case of n-mode channels with noise correlations (i.e. memory), where we focus in particular on the classical additive noise channel. We consider memory models for which the noise correlations can be unraveled by a passive symplectic transformation. Therefore, we can simplify the problem to the study of the Gaussian capacity in an uncorrelated basis, which corresponds to the Gaussian capacity of n single-mode channels with a common input energy constraint. Above an input energy threshold the solutions is given by a global quantum water-filling solution, which implies that all modulated single-mode output states are thermal states with the same temperature. Below the threshold the channels are divided into three sets: i) those that are excluded from information transmission, ii) those for which only the less noisy quadrature is modulated, and iii) those for which the quantum water-filling solution is satisfied. As an example we consider a Gauss-Markov correlated noise, which in the uncorrelated basis corresponds to a collection of single-mode classical additive noise channels. When rotating the collection of optimal single-mode input states back to the original, correlated basis the optimal multi-mode input state becomes a highly entangled state. We then compare the performance of the optimal input state with a simple coherent state encoding and conclude that one gains up to 10% by using the optimal encoding.
Since the preparation of the optimal input state may be very challenging we consider sub-optimal Gaussian-matrix product states (GMPS) as input states as well. GMPS have a known experimental setup and, though being heavily entangled, can be generated sequentially. We demonstrate that for the Markovian correlated noise as well as for a non-Markovian noise model in a wide range of channel parameters, a nearest-neighbor correlated GMPS achieves more than 99.9% of the Gaussian capacity. At last, we introduce a new noise model for which the GMPS is the exact optimal input state. Since GMPS are known to be ground states of quadratic Hamiltonians this suggests a starting point to develop links between optimization problems of quantum communication and many body physics.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
25
Ray, Megan. "Verifying Optical Entanglement." Thesis, University of Oregon, 2013. http://hdl.handle.net/1794/13430.
Full textAbstract:
We look at the problem of verifying optical entanglement for two types of states relevant to quantum information processing. One type occurs in Hong-Ou-Mandel interference and is relevant to quantum computing. The other type is time frequency entanglement which is useful for quantum key distribution. For these types of states the conventional methods of entanglement verification do not work well, and we develop new criteria and methods to verify entanglement of such states. Explicitly, one method takes into account the possible multimode character of two photons, while the other method takes into account the missing data that occur due to the finite range of detectors.
This dissertation includes previously published and unpublished co-authored material.
26
Cai, Yin. "Quantum coherent control with an optical frequency comb." Thesis, Paris, Ecole normale supérieure, 2015. http://www.theses.fr/2015ENSU0030/document.
Full textAbstract:
Les états quantiques multimodes sont au coeur des protocoles detraitement quantique de l’information et de métrologie quantique. Àpartir d’un peigne de fréquence optique injectant un oscillateurparamétrique optique pompé en mode synchrone (SPOPO) nousavons généré des états multimodes en temps/fréquence. Unsimulateur quantique est alors mis en place à partir de ce SPOPO et demise en forme d’impulsion, et permet de mettre en évidence de étatsclusters pouvant compter jusque 12 noeuds et un protocole departage de secret quantique à six partenaires. De plus, une détectionmultipixel résolue en fréquence est développée et utilisée pourréaliser un état cluster linéaire à 8 noeuds. Nous avons égalementutilisé cette source pour développer un spectromètre ayant unesensibilité allant au delà de celle imposée par les fluctuations du videquantiqueMultimode squeezing plays an essential role in quantum informationprocessing and quantum metrology. Using optical frequency combs,we generate multi-temporal-mode state from a synchronouslypumped optical parametric oscillator (SPOPO). An on-demandquantum network simulator is developed using the SPOPO andultrafast pulse shaping; up-to-twelve-node cluster states and asix-partite quantum secret sharing protocol are experimentallyemulated with this simulator. Furthermore, frequency resolvedmultipixel detectors are employed, and used to realize aline-shape-eight-node cluster state. We also developed a multimodequantum spectrometer, which is able to exceed the standardquantum limit for measuring manifold parameters of ultrafast pulses
27
Leedumrongwatthanakun, Saroch. "Quantum information processing with a multimode fibre." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS526.
Full textAbstract:
Le transport à haut débit de données à travers des fibres optiques grâce au multiplexage spatial est en pratique limité par la diaphonie modale. Au lieu de considérer ce couplage modal comme une limitation, nous exploitons ici ce mélange de modes comme une ressource. Nous mettons en oeuvre un réseau optique linéaire programmable basé sur le concept de design photonique inverse, exploitant les techniques de mise en forme du front d’onde. Nous démontrons la manipulation d’interférences quantiques à deux photons sur divers réseaux linéaires, comprenant des degrés de liberté spatiaux et de polarisations. En particulier, nous vérifions expérimentalement la « zero transmission law » dans des interféromètres de Fourier et de Sylvester, permettant de quantifier le degré d’indiscernabilité d’un état d’entrée. De plus, grâce à la possibilité de mettre en oeuvre un réseau non unitaire, nous mettons en évidence l’anti-coalescence de photons dans toutes les configurations de sortie, et réalisons une expérience d’absorption cohérente. Nous démontrons ainsi l’aspect reconfigurable de l’implémentation de tels réseaux optiques linéaires dans des fibres multimodes. De plus, nous étudions les propriétés statistiques du speckle à un et à deux photons générés à partir de divers états d’entrée, après propagation dans une fibre multimode. Ces propriétés statistiques du speckle peuvent être utilisées pour extraire des informations sur la dimensionnalité, la pureté et l’indiscernabilité d’un état quantique inconnu, permettant ainsi leur classification. Ce travail met en évidence le potentiel du contrôle de front d’onde en milieux complexes pour le traitement quantique de l’informationTransport of information through a multimode optical fibre raises challenges when one wants to increase the data traffic using many spatial modes due to modal cross-talk and dispersion. Instead of considering those complex mixing of modes as a detrimental process, in this dissertation, we harness its mode mixing to process quantum optical information. We implement a reconfigurable linear optical network, a fundamental building block for scalable quantum technologies, based on an inverse photonic approach exploiting the technology of wavefront shaping. We experimentally demonstrate manipulation of two-photon quantum interference on various linear optical networks across both spatial and polarization degrees of freedom. In particular, we experimentally show the zero-transmission law in Fourier and Sylvester interferometers, which are used to certificate the degree of indistinguishability of an input state. Moreover, thanks to the ability to implement a non-unitary network, we observe the photon anti-coalescence effect in all output configurations, as well as the realization of a tunable coherent absorption experiment. Therefore, we demonstrate the reconfigurability, accuracy, scalability and robustness of the implemented linear optical networks for quantum information processing. Furthermore, we study the statistical properties of one-and two-photon speckles generated from various ground-truth states of light after propagating through a multimode fibre. These statistical properties of speckles can be used to extract information about the dimensionality, purity, and indistinguishability of an unknown input state of light, therefore allowing for state classification. Our results highlight the potential of complex media combined with wavefront shaping for quantum information processing
28
Arzani, Francesco. "Measurement based quantum information with optical frequency combs." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEE005/document.
Full textAbstract:
Ce manuscrit porte sur l’étude théorique de techniques expérimentales récemment développées pour réaliser des protocoles d’information quantique en variables continues. Les états Gaussiens multi-modes produits par conversion paramétrique de peignes de fréquences optiques jouent un rôle centrale dans ce travail. Ce phénomène permet de générer de façon déterministe un grand nombre d’états Gaussiens de la lumière. L’état de sortie peut ensuite être de-Gaussifié par soustraction ou addition d’un photon dans une superposition cohérente de modes du champ, puis mesuré par détection homodyne. La thèse est organisée en trois projets principaux. Le premier concerne l’optimisation du spectre du laser de pompe pour manipuler l’état de sortie de la conversion paramétrique. Nous avons développé les outils mathématiques pour traiter des profils spectraux avec amplitude et phase spectrales arbitraires. On a ensuite utilisé un algorithme d’optimisation pour trouver les spectres maximisant des différentes propriétés de l’état de sortie. Une importance particulière est donnée à la production d’"états cluster" en variables continues. Les optimisations ont été développées pour prendre en compte les limitations expérimentales pour assurer la faisabilité des forme spectrales dans les expériences. Dans le deuxième projet nous avons étudié comment les états non-Gaussiens obtenus par soustraction d’un photon d’un état comprimé peuvent être utilisés pour le calcul quantique. Nous proposons un protocole inspiré par le paradigme de "calcul quantique basé sur la mesure" qui combine l’état de-Gaussifié et la mesure homodyne pour approximer des opérateurs unitaires non-Gaussiens. On montre que les mêmes résultats peuvent être obtenus avec des mesure projectives sur des états de photon unique. Finalement, le troisième projet porte sur le partage de secret quantique ("quantum secret sharing"). Dans les protocoles de partage de secret quantique un donneur veut distribuer de l’information codée dans un système quantique à plusieurs joueurs d’une façon qui oblige des sous-ensembles de joueurs à collaborer s’ils veulent retrouver l’information originale. Nous avons développé un protocole qui peut être transféré aux expériences de notre groupe et nous avons participé à la formulation d’une preuve de concept expérimentale. À partir de cela, nous avons dérivé des résultats généraux sur le partage et la reconstruction d’états arbitraires de la lumière en utilisant des ressources GaussiennesThe present manuscript reports theoretical investigations about the use of recently developed experimental techniques in the realization of quantum information protocols with continuous variables. The focus of the work is on the multi-mode Gaussian states produced by spontaneous parametric down-conversion of optical frequency combs. Such setup allows to deterministicallyengineer many different Gaussian states of light. The output state can be de-Gaussified subtracting or adding a photon coherently on a superposition of modes and finally measured with pulse-shaped and wavelength-multiplexed homodyne detection. The thesis encompasses three projects. The first concerns the optimization of the spectrum of the pump laser field to engineer the Gaussian output state. We developed mathematical techniques to treat spectral profiles with arbitrary amplitude and spectral phase. We thenran an optimization algorithm to find the spectra maximizing several interesting properties of the state of the down-converted field. A particular emphasis was put on the production of continuous-variable cluster states. The optimizations were developed in such a way as to ensure the experimental feasibility of the optimized pump spectra. In the second project we studied how the non-Gaussian states produced subtracting a photon from a squeezed state can be used for quantum computation. We propose a protocol inspired by the measurement-based paradigm for quantum computation combining the photon subtracted states and homodyne detectionto approximate unitary non-Gaussian operations. We show that the same results can be obtained with projective measurements onsingle-photon states. Finally, the third project deals with quantum secret sharing. In quantum secret sharing schemes a dealer wants to share information encoded in some quantum system with a group of players in such a way that subsets of players need to collaborate if they want to retrieve the information. We devised a secret sharing protocol that could be mapped to the experimental setups developed in our group and participated in the formulation of an experimental proof of principle of such protocol. Starting from this we derived general results for sharing and reconstructing arbitrary quantum states using Gaussian resources
29
Buzbee, Michael Laurence. "3-Dimensional Photonic Circuits for Quantum Information Processing." University of Dayton / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1461970290.
Full text
30
Donati, Gaia. "Hybrid quantum information processing with continuous and discrete variables of light fields." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:673338dc-1233-43c8-be93-11b748a428a9.
Full textAbstract:
Quantum correlations play a fundamental role in quantum information science. The variety of their manifestations has become increasingly apparent following the development of novel light sources, protocols and photodetectors. One broad classification identifies two instances of non-classical correlations: particle and mode entanglement. These categories mirror two coexisting descriptions of quantum systems in terms of discrete and continuous variables of the electromagnetic field. The past decades have generated a number of promising results based on schemes which encompass elements from both frameworks, rather than viewing the two descriptions as mutually exclusive. In this context, it is possible to conceive and realise experiments where either the quantum resource or the detection system is 'hybrid'. Optical weak-field homodyne detectors bring together phase sensitivity and photon counting; as such, they represent a detection scheme which works across continuous and discrete variables of the radiation field. In this thesis we present a two-mode weak-field homodyne detection layout with added photon-number resolution and apply it to the study of a split single-photon state and a squeezed vacuum state. As a first test of the capabilities of this system, we investigate the reconstruction of relevant features of a given quantum resource - such as its photon statistics - with our detection scheme. Further, we experimentally demonstrate the observation of an instance of non-classical optical coherence which combines the continuous- and discrete-variable descriptions explicitly. The ability to probe phenomena at the interface of wave and particle regimes opens the way to novel, improved schemes for quantum information processing. From a more fundamental perspective, such hybrid approaches may shed light on the very roots of quantum enhancement.
31
Sariyanni, Zoe-Elizabeth. "Coherent effects in atomic and molecular media: applications to anthrax detection and quantum information." Texas A&M University, 2006. http://hdl.handle.net/1969.1/4242.
Full textAbstract:
In the present quantum optics and laser physics study, the non-linear interaction
of electromagnetic fields with atomic, molecular and biomolecular media is analyzed.
Particular emphasis is given to coherent phenomena, while propagation and dispersion
effects are also extensively investigated. The fields involved vary from ultra short
pulses to continuous waves; while their energies range from the very strong that are
addressed classically, to the very weak which are described quantum mechanically.
Applications and problems addressed span a wide range. A scheme for a real time
detector of chemical and biological hazards, like anthrax spores, is presented; in it,
a strong spectroscopic signature is obtained from complex molecules by using ultrashort,
femtosecond, laser pulses and inducing vibrational coherence on them. Furthermore,
a way of reversing the phase matching condition in coherent spectroscopy,
based on dispersion, is developed; which allows for the use of such spectroscopic methods
in remote detection. More fundamental questions addressed include a resolution
of the centennial old paradox of Maxwell's demon via quantum thermodynamics, and
the role of atomic coherence in enhancing the efficiency of a heat engine as well as
in obtaining lasing without population inversion. Additionally, a quantum storage
scheme is presented, in which the information contained in an optical pulse is stored
and restored via photon echoes.
32
Gullans, Michael John. "Controlling Atomic, Solid-State and Hybrid Systems for Quantum Information Processing." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11146.
Full textAbstract:
Quantum information science involves the use of precise control over quantum systems to explore new technologies. However, as quantum systems are scaled up they require an ever deeper understanding of many-body physics to achieve the required degree of control. Current experiments are entering a regime which requires active control of a mesoscopic number of coupled quantum systems or quantum bits (qubits). This thesis describes several approaches to this goal and shows how mesoscopic quantum systems can be controlled and utilized for quantum information tasks.Physics
33
Quinn, Niall. "Gaussian non-classical correlations in bipartite dissipative continuous variable quantum systems." Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/6915.
Full textAbstract:
This thesis probes the usefulness of non-classical correlations within imperfect continuous variable decoherent quantum systems. Although a consistent function and practical usefulness of these correlations is largely unknown, it is important to examine their characteristics in more realistic dissipative systems, to gain further insight into any possible advantageous behaviour. A bipartite separable discordant state under the action of controlled loss on one subsystem was considered. Under these conditions the Gaussian quantum discord not only proved to be robust against loss, but actually improves as loss is intensified. Harmful imperfections which reduce the achievable level of discord can be counteracted by this controlled loss. Through a purification an explanation of this effect was sought by considering system-environment correlations, and found that a flow of system-environment correlations increases the quantumness of the state. Entanglement recovery possibilities were discussed and revealed the importance of hidden quantum correlations along bi-partitions across the discordant state and a classically prepared "demodulating" system, acting in such a way as to partially cancel the entanglement preventing noise. Entanglement distribution by separable states was studied by a similar framework, in an attempt to explain the emergence of quantum entanglement by a specific flow of correlations in the globally pure system. Discord appears to play a less fundamental role compared to the qubit version of the protocol. The strengthening of non-classical correlations can be attributed to a flow of classical and quantum correlations. This work proves that discord can be created in unique ways and, in select circumstances, can act to counteract harmful imperfections in the apparatus. Due to this advantageous behaviour discord indeed may ultimately aid in more applicable "real world" applications, which are by definition decoherent.
34
Shih, Chung-Yu. "Characterizing single atom dipole traps for quantum information applications." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47607.
Full textAbstract:
Ultracold neutral atoms confined in optical dipole traps have important applications in quantum computation and information processing, quantum simulators of interacting-many-body systems and atomic frequency metrology. While optical dipole traps are powerful tools for cold atom experiments, the energy level structures of the trapped atoms are shifted by the trapping field, and it is important to characterize these shifts in order to accurately manipulate and control the quantum state of the system.
In order to measure the light shifts, we have designed a system that allows us to reliably trap individual 87Rb atoms. A non-destructive detection technique is employed so that the trapped atoms can be continuously observed for over 100 seconds. Single atom spectroscopy, trap frequency measurements, and temperature measurements are performed on single atoms in a single focus trap and small number of atoms in a 1D optical lattice in order to characterize the trapping environment, the perturbed energy level structures, and the probe-induced heating.
In the second part of the thesis, we demonstrate deterministic delivery of an array of individual atoms to an optical cavity and selective addressability of individual atoms in a 1D optical conveyor, which serves as a potential candidate for scalable quantum information processing. The experiment is extended to a dual lattice system coupled to a single cavity with the capability of independent lattice control and addressability. The mutual interactions of atoms in different lattices mediated by a common cavity field are demonstrated. A semi-classical model in the many-atom regime based on the Jaynes-Cummings model is developed to describe the system that is in good qualitative agreement with the data. This work provides a foundation for developing multi-qubit quantum information experiments with a dual lattice cavity system.
35
Djordjevic, Ivan B. "Integrated Optics Modules Based Proposal for Quantum Information Processing, Teleportation, QKD, and Quantum Error Correction Employing Photon Angular Momentum." IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2016. http://hdl.handle.net/10150/615122.
Full textAbstract:
To address key challenges for both quantum communication and quantum computing applications in a simultaneous manner, we propose to employ the photon angular momentum approach by invoking the well-known fact that photons carry both the spin angular momentum (SAM) and the orbital angular momentum (OAM). SAM is associated with polarization, while OAM is associated with azimuthal phase dependence of the complex electric field. Given that OAM eigenstates are mutually orthogonal, in principle, an arbitrary number of bits per single photon can be transmitted. The ability to generate/analyze states with different photon angular momentum, by using either holographic or interferometric methods, allows the realization of quantum states in multidimensional Hilbert space. Because OAM states provide an infinite basis state, while SAM states are 2-D only, the OAM can also be used to increase the security for quantum key distribution (QKD) applications and improve computational power for quantum computing applications. The goal of this paper is to describe photon angular momentum based deterministic universal quantum qudit gates, namely, {generalized-X, generalized-Z, generalized-CNOT} qudit gates, and different quantum modules of importance for various applications, including (fault-tolerant) quantum computing, teleportation, QKD, and quantum error correction. For instance, the basic quantum modules for quantum teleportation applications include the generalized-Bell-state generation module and the QFT-module. The basic quantum module for quantum error correction and fault-tolerant computing is the nonbinary syndrome calculator module. The basic module for entanglement assisted QKD is either the generalized-Bell-state generation module or the Weyl-operator-module. The possibility of implementing all these modules in integrated optics is discussed as well. Finally, we provide security analysis of entanglement assisted multidimensional QKD protocols, employing the proposed qudit modules, by taking into account the imperfect generation of OAM modes.
36
Clark, Alex S. "Quantum information processing in optical fibres." Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557975.
Full textAbstract:
The use of quantum particles provides unprecedented improvements for some computational tasks and has applications in provably secure communications. The choice of quantum particles for such processes is wide but single photons are a promising candidate due to their extremely low decoherence and light speed trans- mission. Current technology for the generation and processing of single photons is of exceptional experimental interest and forms the basis of my investigations in this thesis. I show the background theory of quantum information and communication, with a general analysis of qubits and optical quantum gates before looking more specifically at different sources of photonic qubits and the generation of photons. I then show recent improvements in photon generation using photonic crystal fi- bres (PCFs), most especially the use of cross-polar phase matching solutions that allow the generation of pure state photons via four wave mixing effects in a X(3} nonlinear medium. These therefore require no spectral filtering to be used for quantum information tasks, thereby improving collection rates and experimental integration times which are crucial when performing multi-photon experiments. The optimization of the parameters for such a source are achieved through the use of an analytical model, and the purity of the photons are tested through the use of quantum interference effects. I move on to show the construction and character- ization of a common two qubit gate, namely the controlled-NOT gate, in optical fibres using fibre based sources and describe it's usefulness and integrability into quantum communication networks. I then calculate bounds on the average gate fidelity of 0.83 < Fave < 0.91 and create a model to show the main sources of error in the controlled-NOT gate operation. If the PCF used in the above sources is pumped in opposite directions in a Sagnac loop configuration, pairs of photons are generated in a maximally entangled Bell state where the polarization of one photon is perfectly correlated with the other photon of the pair. If two such pairs are generated in separate sources and one photon from each pair mixed on a polarizing beam splitter, a fusion operation is performed that entangles those two photons creating a four photon cluster state where all photons are entangled. This cluster state is a universal resource for measurement based quantum computing. In this thesis I show the generation and characterisation of such a cluster state and describe its use to perform a universal set of gates through single qubit measurements. I finally describe future experiments using PCFs and cluster states.
37
Amselem, Elias. "Dynamics of Quantum Correlations with Photons : Experiments on bound entanglement and contextuality for application in quantum information." Doctoral thesis, Stockholms universitet, Fysikum, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-66469.
Full textAbstract:
The rapidly developing interdisciplinary field of quantum information, which merges quantum and information science, studies non-classical aspects of quantum systems. These studies are motivated by the promise that the non-classicality can be used to solve tasks more efficiently than classical methods would allow. In many quantum informational studies, non-classical behaviour is attributed to the notion of entanglement. In this thesis we use photons to experimentally investigate fundamental questions such as: What happens to the entanglement in a system when it is affected by noise? In our study of noisy entanglement we pursue the challenging task of creating bound entanglement. Bound entangled states are created through an irreversible process that requires entanglement. Once in the bound regime, entanglement cannot be distilled out through local operations assisted by classical communication. We show that it is possible to experimentally produce four-photon bound entangled states and that a violation of a Bell inequality can be achieved. Moreover, we demonstrate an entanglement-unlocking protocol by relaxing the condition of local operations. We also explore the non-classical nature of quantum mechanics in several single-photon experiments. In these experiments, we show the violation of various inequalities that were derived under the assumption of non-contextuality. Using qutrits we construct and demonstrate the simplest possible test that offers a discrepancy between classical and quantum theory. Furthermore, we perform an experiment in the spirit of the Kochen-Specker theorem to illustrate the state-independence of this theorem. Here, we investigate whether or not measurement outcomes exhibit fully contextual correlations. That is, no part of the correlations can be attributed to the non-contextual theory. Our results show that only a small part of the experimental generated correlations are amenable to a non-contextual interpretation.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 5: Submitted. Paper 6: Submitted.
38
Thomas-Peter, Nicholas. "Quantum enhanced precision measurement and information processing with integrated photonics." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:7bd47582-d32f-4d07-9e90-4978c32cf14e.
Full textAbstract:
Photons have proven to be an effective test-bed for the fundamental concepts and elements of quantum-enhanced technologies. As systems become increasingly complex, however, practical considerations make the traditional approach of bulk optics and free-space propagation progressively more difficult. The major obstacles are the physical space necessary to realise and operate such a complex system, its stability, and maintaining low losses. In order to address these issues, quantum optical technologies can take a cue from their classical counterparts and look towards an integrated architecture to provide miniaturisation, greatly enhanced stability, less alignment, and low loss interfaces between different system components. In this thesis the feasibility of chip-based waveguides as a platform for metrology and information processing will be explored. In Part I, the necessary criteria for a metrology system to out-perform its classical counterpart will be investigated. It will be found that loss is a major barrier to this aim and, critically, that it is unlikely to have been achieved to date by any experiment which consumes resources of a fixed photon number. The issue of loss will be addressed by developing a scalable heralded source of a class of entangled photonic states which are both robust to losses and practically feasible to prepare. A novel tomographic technique will be developed to characterize these states and it will be explicitly demonstrated how it is possible to beat some bounds on classical performance without being able to out-perform a comparable classical system. Finally, a proof of principle demonstration of a waveguide-based interferometer with an integrated phase-shifter will be undertaken. It will be shown that the device preserves quantum interference, making it suitable for use in quantum-enhanced metrology applications. In Part II, integrated optics in the context of information processing will be discussed. First, a novel characterization technique will be developed which enables the behaviour of complex circuits to be predicted. The technique is independent of loss in the device being characterized. A method of simulating these circuits will be outlined that takes advantage of the computational speed-up available from parallelisation and sparse matrix operations. A key increase in complexity for integrated photonic systems will be demonstrated by showing quantum interference of three photons from two separate sources in eight spatial modes. The resulting interference has a visibility which beats all possible classical interference visibilities for similar circuits. Finally, a fully integrated waveguide-coupled photon-number-resolving detector will be developed and demonstrated. This proof of concept demonstration will show good resolution of different photon number events. The device will be modelled and routes to high efficiency operation will be explored.
39
Hameedi, Muhammad Alley. "Single Photon Sources and Single Quantum System enabled Communication." Doctoral thesis, Stockholms universitet, Fysikum, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-139095.
Full textAbstract:
Quantum information is a highly interesting and fast emerging field that involves processing information encoded into quantum systems and their subsequent use in various information tasks. The use of quantum resources such as superposition and entanglement have shown to enhance information processing capabilities beyond classical means in a number of communication, information and computation tasks. In this thesis, we have used single photons to study the advantage of d-level quantum systems (qudits) for a communication task commonly known as random access codes (RACs). A successful experimental demonstration of quantum random access codes (QRACs) with four dimensions is realized to demonstrate that the higher dimensional QRACs not only outperform the classical RACs but also provide an advantage over their quantum bit (qubit) counterparts. QRACs are also studied in regards to two specific applications: certification of true randomness and for testing the non-classicality of quantum systems. A method for increased certification of generated randomness is realized for the former and a successful experimental demonstration of a test of non-classicality with arbitrarily low detection efficiency is provided for the latter. This is followed by an implementation of a QRAC in a one-path communication network consisting of preparation, transformation and measurement devices. We have shown that the distributed QRAC provides optimal success probabilities for a number of tasks. Moreover, a novel quantum protocol for the solution to the problem of dining cryptographers and anonymous veto voting is also presented. This single photon transmission based protocol provides an efficient solution, which is experimentally demonstrated for a 3-party description. Lastly, Nitrogen-Vacancy (NV) center in diamond is studied as a potential resource for single photon emission and two methods to enhance the photon collection efficiency are successfully explored. Due to this enhancement, single photons from an NV center may also be used in similar single quantum system based communication experiments.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.
40
Jen, Hsiang-Hua. "Theory of light-matter interactions in cascade and diamond type atomic ensembles." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37288.
Full textAbstract:
In this thesis, we investigate the quantum mechanical interaction of light with matter in the form of a gas of ultracold atoms: the atomic ensemble. We present a theoretical analysis of two problems, which involve the interaction of quantized electromagnetic fields (called signal and idler) with the atomic ensemble (i) cascade two-photon emission in an atomic ladder configuration, and (ii) photon frequency conversion in an atomic diamond configuration. The motivation of these studies comes from potential applications in long-distance quantum communication where it is desirable to generate quantum correlations between telecommunication wavelength light fields and ground level atomic coherences. In the two systems of interest, the light field produced in the upper arm of an atomic Rb level scheme is chosen to lie in the telecom window. The other field, resonant on a ground level transition, is in the near-infrared region of the spectrum. Telecom light is useful as it minimizes losses in the optical fiber transmission links of any two long-distance quantum communication device.
We develop a theory of correlated signal-idler pair correlation. The analysis is complicated by the possible generation of multiple excitations in the atomic ensemble. An analytical treatment is given in the limit of a single excitation assuming adiabatic laser excitations. The analysis predicts superradiant timescales in the idler emission in agreement with experimental observation. To relax the restriction of a single excitation, we develop a different theory of cascade emission, which is solved by numerical simulation of classical stochastic differential equation using the theory of open quantum systems. The simulations are in good qualitative agreement with the analytical theory of superradiant timescales. We further analyze the feasibility of this two-photn source to realize the DLCZ protocol of the quantum repeater communication system.
We provide a quantum theory of near-infrared to telecom wavelength conversion in the diamond configuration. The system provides a crucial part of a quantum-repeater memory element, which enables a "stored" near-infrared photon to be converted to a telecom wavelength for transmission without the destruction of light-atom quantum correlation. We calculate the theoretical conversion efficiency, analyzing the role of optical depth of the ensemble, pulse length, and quantum fluctuations on the process.
41
Thomas, Peter James. "The application of spontaneous parametric downconversion to develop tools for validating photonic quantum information technologies." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/3050.
Full textAbstract:
This portfolio of work contributes to the remit of the National Physical Laboratory (NPL) to develop the underpinning expertise and tools for validating nascent and future optical quantum technologies based on the discrete and quantum properties of photons. This requirement overlaps with the requirement to provide validation for devices operating in the photon-counting regime. A common theme running through the portfolio is photon pairs generated through spontaneous parametric downconversion (SPDC). A Hong-Ou-Mandel (HOM) interferometer sourced with visible wavelength photon pairs from an SPDC process in beta-barium borate (BBO) was designed, built and characterised. The visibility of the HOM interference is dependent on the indistinguishability of the interfering photons, but is also influenced by imperfections of the interferometer; therefore an investigation was carried out to quantify the effects of the interferometer imperfections on the measured visibility so that the true photon indistinguishability could be measured with a quantified uncertainty. A bright source of correlated pair photons in the telecoms band based upon a pump enhanced SPDC process in periodically-poled potassium titanyl phosphate (PPKTP) was designed, built and characterised. From the characterisation measurements the source brightness was estimated to be 6.2×10⁴ pairs/ s/ mw pump. The photon pairs were further characterised through their incorporation as a source in a HOM interference experiment. The developed correlated photon pair source was at the heart of a novel scheme for the generation of polarisation entangled photon pairs, for which the design, build and characterisation work is presented. The source was demonstrated to produce two of the four maximally entangled Bell states with quantum interference visibilities of around 0.95. The generated states were also shown to break a form of Bell's inequality by around six standard deviations. The polarisation entangled photon pair source was originally built at the University of St Andrews and was later transferred to the NPL where it will extend NPL's capabilities to this key spectral region. Finally a study was carried out to investigate the possibility of a wavelength tuneable device for the absolute measurement of single photon detector quantum efficiencies based upon an established SPDC technique.
42
Rakreungdet, Worawarong. "Quantum Information Science with Neutral Atoms." Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/194406.
Full textAbstract:
We study a system of neutral atoms trapped in a three-dimensional optical lattice suitable for the encoding, initialization and manipulation of atomic qubits. The qubits are manipulated by applied electromagnetic fields interacting with dipole moments of the atoms via light shifts, Raman transitions, Zeeman shifts, and microwave transitions. Our lattice is formed by three orthogonal one-dimensional lattices, which have different frequencies so that interference terms average to zero. This geometry allows considerable freedom in designing the component one-dimensional lattices, so that they provide not only confinement but also independent control in each dimension. Our atomic qubits are initialized from a laser-cooled atomic sample by Raman sideband cooling in individual lattice potential wells. We have demonstrated accurate and robust one-qubit manipulation using resonant microwave fields. In practice such control operations are always subject to errors, in our case spatial inhomogeneities in the microwave Rabi frequency and the light shifted qubit transition frequency. Observation of qubit dynamics in near real time allows us to minimize these inhomogeneities, and therefore optimize qubit logic gates. For qubits in the lattice, we infer a fidelity of 0.990(3) for a single pi-pulse. We have also explored the use of NMR-type pulse techniques in order to further reduce the effect of errors and thus improve gate robustness in the atom/lattice system. Our schemes for two-qubit quantum logic operations are based on controlled collisional interactions. We have experimented with two schemes in order to probe these collisions. The first involves manipulation of the center-of-mass wavepackets of two qubits in a geometry corresponding to two partially overlapping Mach-Zender interferometers. Unfortunately, this scheme has proven extremely sensitive to phase errors, as the wavepackets are moved by the optical lattice. The other scheme starts with two qubits in spatially separated traps, and utilizes microwaves to drive one or both qubits into a third trap in-between the two qubits. Once the wavepackets overlap, the collisions create a large energy shift which can be probed spectroscopically.
43
Fabre, Nicolas. "Quantum information in time-frequency continuous variables." Thesis, Université de Paris (2019-....), 2020. http://www.theses.fr/2020UNIP7044.
Full textAbstract:
Cette thèse aborde l’encodage de degrés de liberté continus temps-fréquence de photon uniques. Les similitudes mathématiques avec les quadratures du champ électromagnétique amène à généraliser des protocoles exprimées dans ces variables dans notre encodage. On introduit un nouveau type de qubit robuste contre des erreurs du type déplacement dans l’espace des phases temps-fréquence. Un nouvel espace des phases doublement cylindriques est étudié et est une représentation particulièrement adaptée pour des états ayant une symétrie de translation. On étudie également comment construire une distribution de phase fonctionnelle permettant de décrire un état quantique possédant des degrés de libertés continus spectraux et en quadratureThis thesis tackles the time-frequency continuous variables degree of freedom encoding of single photons and examine the formal mathematical analogy with the quadrature continuous variables of the electromagnetic field. We define a new type of qubit which is robust against time-frequency displacement errors. We define a new double-cylinder phase space which is particularly adapted for states which have a translational symmetry. We also study how to build a functional phase space distribution which allows to describe a quantum state with spectral and quadrature continuous variables degrees of freedom
44
Reim, Klaus Franz. "Broadband optical quantum memory." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:d0d73ed2-32c2-4de9-8b3d-fcf8b88b22b4.
Full textAbstract:
This thesis is about the experimental implementation of a high-speed and robust quantum memory for light. A novel far off-resonant Raman approach to ensemble-based quantum memories in a room-temperature environment is developed and demonstrated. Storage and retrieval of sub-nanosecond, weak coherent light pulses at the single-photon-level with total efficiencies exceeding 30% and storage times of up to 4 μs are achieved. The coherence of the memory is shown by directly interfering a copy of the incident signal with the retrieved signal from the memory. The unconditional noise floor of the memory is found to be low enough to operate the memory in the quantum regime at room temperature. Multiple readout of a single stored excitation is demonstrated, suggesting that 100% readout is possible in different temporal modes. Furthermore, first results regarding the storage and retrieval of polarisation encoded qubits are obtained. This and the memory’s ability to operate in the quantum regime at room temperature with a low unconditional noise floor illustrate its potential usefulness for real world applications.
45
Flurin, Emmanuel. "The Josephson mixer : a swiss army knife for microwave quantum optics." Thesis, Paris, Ecole normale supérieure, 2014. http://www.theses.fr/2014ENSU0024/document.
Full textAbstract:
Cette thèse explore les caractéristiques uniques offertes par le mélangeur Josephson dans le domaine émergeant de l’optique quantique micro-onde. Nous avons démontré que le mixeur Josephson pouvait jouer trois rôles majeurs pour le traitement de l’information quantique. Nous avons conçu et fabriqué un amplificateur à la limite quantique avec la meilleure efficacité quantique démontrée à cette date. Cet outil crucial peut être utilisé pour la mesure microonde de systèmes mésoscopiques dont les circuits supraconducteurs. En particulier, cela nous a permis de réaliser avec succès la stabilisation de trajectoires d’un bit quantique supraconducteur par rétroaction basée sur la mesure. Ensuite, nous avons montré comment ce circuit peut générer et distribuer des radiations micro-ondes intriquées par conversion paramétrique spontanée sur des lignes de transmissions séparées dans l’espace et à des fréquences différentes. En utilisant deux mixeurs Josephson, nous avons fourni la première démonstration d’intrication non- locale entre deux champs propageants dans le domaine micro-onde, les états dits EPR. Finalement, nous avons utilisé le mixeur Josephson dans le mode de conversion de fréquence. Il se comporte alors comme un interrupteur, permettant d’ouvrir ou fermer dynamiquement l’accès à une cavité de haut facteur de qualité. L’ensemble constitue une mémoire quantique. En combinant cela avec la génération d’intrication, nous avons mesuré la distribution, le stockage et la libération sur demande d’un état intriqué. Ceci est un pré-requis pour jouer le rôle de nœud au sein d’un réseau quantiqueThis thesis work explores unique features offered by the Josephson mixer in the upcoming field of microwave quantum optics. We have demonstrated three major roles the Josephson mixer could play in emerging quantum information architectures. First, we have designed and fabricated a state-of-the-art practical quantum limited amplifier with the best quantum efficiency achieved to date. This tool is crucial for probing mesoscopic systems with microwaves, and in particular superconducting circuits. Hence, it has enabled us to realize successfully the stabilization of quantum trajectories of a superconducting qubit by measurement-based feedback. Second, we have shown how this circuit can generate and distribute entangled microwave radiations on separated transmission lines at different frequencies. Using two Josephson mixers, we have provided the first demonstration of entanglement between spatially separated propagating fields in the microwave domain, the so-called Einstein-Podolsky-Rosen states. Finally, we have used the Josephson mixer as a frequency converter. Acting as a switch, it is able to dynamically turn on and off the coupling to a low loss cavity. This feature allowed us to realize a quantum memory for microwaves. In combination with the ability to generate entanglement, we have measured the time-controlled generation, storage and on-demand release of an entangled state, which is a prerequisite for nodes of a quantum network
46
Zimmer, Frank E. "Matter-wave optics of dark-state polaritons applications to interferometry and quantum information /." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=982522533.
Full text
47
Gibbons, Michael J. "Robust, reusable qubits for quantum information applications." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39474.
Full textAbstract:
Most neutral atom quantum computing experiments rely on destructive state detection techniques that eject the detected qubits from the trap. These techniques limit the repetition rate of these experiments due to the necessity of reloading a new quantum register for each operation.
We address this problem by developing reusable neutral atom qubits. Individual Rubidium 87 atoms are trapped in an optical lattice and are held for upwards of 300 s. Each atom is prepared in an initial quantum state and then the state is subsequently detected with 95% fidelity with less than a 1% probability of losing it from the trap. This combination of long storage times and nondestructive state detection will facilitate the development of faster and more complex quantum systems that will enable future advancements in the field of quantum information.
48
Viscor, Pagès Daniel. "From quantum memories to single-site addressing with three-level atoms." Doctoral thesis, Universitat Autònoma de Barcelona, 2013. http://hdl.handle.net/10803/117482.
Full textAbstract:
El camp de la informació quàntica, que sorgeix de la combinació entre la teoria de la informació i la física quàntica, ha experimentat un enorme progrés durant les darreres dècades, donant lloc a avenços revolucionaris en una àmplia varietat de camps interdisciplinaris, com ara la computació quàntica, la comunicació quàntica, els mesuraments d'alta precisió, i l’estudi fonamental de la teoria quàntica. No obstant això, les ambicioses metes en què la comunitat científica esta centrada, per exemple, la criptografia quàntica, els simuladors quàntics, o fins i tot la computació quàntica, tot just han començat a destacar.En la majoria d'aplicacions de la informació quàntica, per tal d’emmagatzemar i processar la informació s'utilitzen normalment sistemes amb un gran nombre d’àtoms, mentre que la llum s'utilitza com una eina per a manipular i realitzar operacions lògiques, així com per transmetre els bits quàntics entre nodes distants d'una xarxa quàntica. Per tant, la realització d'una interfície adequada entre la llum i els conjunts d’àtoms és essencial en la ciència de la informació quàntica. Quant a la interacció llum-matèria, un dels sistemes més rellevants són els àtoms de tres nivells en interacció amb un parell de camps electromagnètics. Els sistemes de tres nivells mostren una rica varietat de fenòmens quàntics a causa de les interferències produïdes degut a les dues vies d'absorció de la llum. Aquestes interferències quàntiques donen lloc, per exemple, a l’atrapament coherent de població, la transparència induïda electromagnèticament, o el passatge adiabàtic via estimulació Raman, que han trobat aplicacions en moltes àrees de la informació quàntica.Aquesta tesi, que recull el treball d'investigació que he realitzat durant el meu doctorat sota la guia i el suport dels meus supervisors i col•laboradors, se centra principalment en aplicacions de la informació quàntica amb àtoms de tres nivells en interacció amb camps electromagnètics, tant a nivell semi clàssic i com completament quàntic. Els tres primers capítols de l'obra es centren en l'estudi teòric de nous mètodes per implementar memòries quàntiques per qubits de fotons individuals en superposició de dues components, tant de la polarització com de la freqüència. Les memòries quàntiques són dispositius capaços d'emmagatzemar i recuperar a voluntat estats quàntics de la llum amb una alta eficiència i fidelitat, i són components essencials en moltes aplicacions de la informació quàntica, com ara en repetidors quàntics o en fonts de fotons individuals. Així, l'estudi de mètodes per emmagatzemar diferents tipus de codificació de la informació quàntica en fotons és una tasca essencial.D'altra banda, propostes addicionals en el context del processat d'informació quàntica, dutes a terme durant el meu doctorat, es recullen en els capítols finals. En particular, primer ens centrem en el problema de l’adreçament de llocs individuals per àtoms neutres ultra freds en xarxes òptiques amb un àtom per lloc. Aquesta proposta es du a terme mitjançant l'ús d'una tècnica de passatge adiabàtic selectiu segons la posició. A més, en segon lloc ampliem un model teòric capaç de proporcionar prediccions fiables sobre un experiment per a la producció de parells de fotons individuals, d’alta puresa i ample de banda controlat, utilitzant una configuració de conversió paramètrica espontània.Quantum information science, which emerges from the combination of information theory and quantum physics, has experienced an enormous progress during the last decades, leading to revolutionary advances in a wide range of interdisciplinary fields, such as quantum computation, quantum communication, high precision measurements, and fundamental quantum science. However, the ambitious goals at which the scientific community aim, e.g., quantum criptography, quantum simulators, or even quantum computation, have only started to stand out.In most quantum information applications, atomic ensembles are normally used to store and process the information, while light is used as a tool to manipulate and perform logical operations, as well as to transmit the quantum bits between distant nodes of a quantum network. Thus, the realization of a suitable quantum interface between light and atomic ensembles is essential in quantum information science. Regarding light-matter interaction, one of the most relevant systems are three-level atoms in interaction with a pair of electromagnetic fields. Three-level systems exhibit a rich variety of phenomena due to quantum interferences between the two absorption paths for the light. These quantum interferences lead, for instance, to coherent population trapping, electromagnetically induced transparency, or stimulated Raman adiabatic passage, which have found applications in many areas of quantum information. This thesis, which collects the research work that I have performed during my PhD under the guidance and support of my supervisors and collaborators, is mainly focused in quantum information applications using three level atoms in interaction with electromagnetic fields both at the semiclassical and fully quantum levels. The first three chapters of the work are focused on the theoretical study of novel methods to implement quantum memories for single photon qubits in superposition of two components, either polarization or frequency. Quantum memories are devices capable of storing and retrieving on demand quantum states of light with high efficiency and fidelity, and are essential components in many quantum information applications, such as quantum repeaters or single photon sources. Thus, the study of methods to store different kinds of quantum information encoding in photons is an essential task.Moreover, additional work in quantum information processing done during my PhD is collected in the final chapters. In particular, first we focus on the problem of single site addressing of ultracold neutral atoms in optical lattices with one atom per site, by using a position selective adiabatic passage technique. Next, we extend a theoretical model capable of providing reliable predictions for the production of controlled bandwidth and pure single photon pairs experiment, using a spontaneous parametric down-conversion setup.
49
Domeneguetti, Renato Ribeiro. "Ruídos quânticos da luz em macro cavidade de fibra óptica." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-26092014-152240/.
Full textAbstract:
Mistura de quatro ondas não degenerada em fibras ópticas na configuração de cavidade foi inicialmente proposto como forma de geração de estados comprimidos da luz. Neste trabalho desenvolvemos um tratamento pura- mente quântico da análise da interação não linear entre a luz e a matéria. Com a equação de Fokker-Planck na representação de Wigner obtemos di- retamente das equações o limiar de oscilação dos feixes gêmeos e o efeito de biestabilidade. Das equações de dinâmica linearizadas para as flutuações de quadraturas confirmamos a geração de estados comprimidos provenientes do processo de 4WM, tanto abaixo quanto acima do limiar de oscilação. Não é possível iniciar a geração dos feixes gêmeos sem antes alcançar o limiar de oscilação do espalhamento Brillouin estimulado. Portanto, técnicas para aumentar este limiar devem ser empregadas em qualquer medida de ruído ao nível de shot-noise com geração de campos. Nós também testamos as limitações técnicas intrínsecas do laser de diodo, como o ruído de amplitude e fase, assim como sua estabilidade em um experimento interferômetrico. Abaixo do limiar, a cavidade atua no sentido de reduzir o ruído de fase do laser em um intervalo de frequência que vai de 10MHz a 80MHz.Nondegenarate four-wave mixing in an optical-fiber cavity geometry, was initially proposed as a mean to generate squeezed states of light. We developed in this work a purely quantum analyzis of the nonlinear interaction between light and medium. With Fokker-Planck equation in the Wigner representation, we obtained directly from the equations, the twin beams oscillation threshold and bistability. From the linearized dynamic equations for the quadratures fluctuations, we confirmed the generation of squeezed states proceeding from 4WM process, not only below but above the threshold oscillation. It is not possible to initiate the twin beams generation without first reaching the stimulated Brillouin scattering threshold. Therefore, techniques to increase this threshold, must be used for any noise measure to the shot-noise level with fields generation. We also have tested the technical limitations of laser diode, as amplitude and phase noise, as well as the stability in an interferometric experiment. Below threshold, the cavity acts in the sense of reducing the intrinsic laser phase noise in a frequency range that goes from 10MHz to 80MHz.
50
Leung, Calvin. "Quantum Foundations with Astronomical Photons." Scholarship @ Claremont, 2017. http://scholarship.claremont.edu/hmc_theses/98.
Full textAbstract:
Theoretical work in quantum information has demonstrated that a classical hidden-variable model of an entangled singlet state can explain nonclassical correlations observed in tests of Bell’s inequality if while measuring the Bell correlation, the underlying probability distribution of the hidden-variable changes depending on the measurement basis. To rule out this possibility, distant quasars can be utilized as random number generators to set measurement bases in an experimental test of Bell’s inequality. Here we report on the design and characterization of a device that uses the color of incoming quasar photons to output a random bit with nanosecond latency. Through the 1-meter telescope at JPL Table Mountain Observatory, we observe and generate random bits from quasars with redshifts z = 0.1−3.9. In addition, we formulate a mathematical model that quantifies the fidelity of the bits generated.