Dissertations / Theses on the topic 'Quantum information processing'
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Hutton, Alexander. "Networked quantum information processing." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403741.
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Chan, Ka Ho Adrian. "Quantum information processing with semiconductor quantum dots." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648684.
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Xu, Xiulai. "InAs quantum dots for quantum information processing." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615012.
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Close, Tom A. "Robust quantum phenomena for quantum information processing." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:95324cad-e44b-4bd8-b6e1-173753959993.
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This thesis is concerned with finding technologically useful quantum phenomena that are robust against real world imperfections. We examine three different areas covering techniques for spin measurement, photon preparation and error correction. The first research chapter presents a robust spin-measurement procedure, using an amplification approach: the state of the spin is propagated over a two-dimensional array to a point where it can be measured using standard macroscopic state mea- surement techniques. Even in the presence of decoherence, our two-dimensional scheme allows a linear growth in the total spin polarisation - an important increase over the √t obtainable in one-dimension. The work is an example of how simple propagation rules can lead to predictable macroscopic behaviour and the techniques should be applicable in other state propagation schemes. The next chapter is concerned with strategies for obtaining a robust and reliable single photon source. Using a microscopic model of electron-phonon interactions and a quantum master equation, we examine phonon-induced decoherence and assess its impact on the rate of production, and indistinguishability, of single photons emitted from an optically driven quantum dot system. We find that, above a certain threshold of desired indistinguishability, it is possible to mitigate the deleterious effects of phonons by exploiting a three-level Raman process for photon production. We introduce a master equation technique for quantum jump situations that should have wide application in other situations. The final chapter focusses on toric error correcting codes. Toric codes form part of the class of surface codes that have attracted a lot of attention due to their ability to tolerate a high level of errors, using only local operations. We investigate the power of small scale toric codes and determine the minimum size of code necessary for a first experimental demonstration of toric coding power.
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Rossini, Davide. "Quantum information processing and Quantum spin systems." Doctoral thesis, Scuola Normale Superiore, 2007. http://hdl.handle.net/11384/85856.
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Le, Jeannic Hanna. "Optical Hybrid Quantum Information processing." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066596/document.
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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
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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.
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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.
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Mezher, Rawad. "Randomness for quantum information processing." Electronic Thesis or Diss., Sorbonne université, 2019. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2019SORUS244.pdf.
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Cette thèse est basée sur la génération et la compréhension de types particuliers des ensembles unitaires aleatoires. Ces ensembles est utile pour de nombreuses applications de physique et de l’Information Quantique, comme le benchmarking aléatoire, la physique des trous noirs, ainsi qu’à la démonstration de ce que l’on appelle un "quantum speedup" etc. D'une part, nous explorons comment générer une forme particulière d'évolution aléatoire appelée epsilon-approximateunitary t-designs . D'autre part, nous montrons comment cela peut également donner des exemples de quantum speedup, où les ordinateurs classiques ne peuvent pas simuler en temps polynomiale le caractère aléatoire. Nous montrons également que cela est toujours possible dans des environnements bruyants et réalistesThis thesis is focused on the generation and understanding of particular kinds of quantum randomness. Randomness is useful for many tasks in physics and information processing, from randomized benchmarking , to black hole physics , as well demonstrating a so-called quantum speedup , and many other applications. On the one hand we explore how to generate a particular form of random evolution known as a t-design. On the other we show how this can also give instances for quantum speedup - where classical computers cannot simulate the randomness efficiently. We also show that this is still possible in noisy realistic settings. More specifically, this thesis is centered around three main topics. The first of these being the generation of epsilon-approximate unitary t-designs. In this direction, we first show that non-adaptive, fixed measurements on a graph state composed of poly(n,t,log(1/epsilon)) qubits, and with a regular structure (that of a brickwork state) effectively give rise to a random unitary ensemble which is a epsilon-approximate t-design. This work is presented in Chapter 3. Before this work, it was known that non-adaptive fixed XY measurements on a graph state give rise to unitary t-designs , however the graph states used there were of complicated structure and were therefore not natural candidates for measurement based quantum computing (MBQC), and the circuits to make them were complicated. The novelty in our work is showing that t-designs can be generated by fixed, non-adaptive measurements on graph states whose underlying graphs are regular 2D lattices. These graph states are universal resources for MBQC. Therefore, our result allows the natural integration of unitary t-designs, which provide a notion of quantum pseudorandomness which is very useful in quantum algorithms, into quantum algorithms running in MBQC. Moreover, in the circuit picture this construction for t-designs may be viewed as a constant depth quantum circuit, albeit with a polynomial number of ancillas. We then provide new constructions of epsilon-approximate unitary t-designs both in the circuit model and in MBQC which are based on a relaxation of technical requirements in previous constructions. These constructions are found in Chapters 4 and 5
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Chubb, Christopher. "Noise in Quantum Information Processing." Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/20682.
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Quantum phenomena such as superposition and entanglement imbue quantum systems with information processing power in excess of their classical counterparts. These properties of quantum states are, however, highly fragile. As we enter the era of noisy intermediate-scale quantum (NISQ) devices, this vulnerability to noise is a major hurdle to the experimental realisation of quantum technologies. In this thesis we explore the role of noise in quantum information processing from two different perspectives. In Part I we consider noise from the perspective of quantum error correcting codes. Error correcting codes are often analysed with respect to simplified toy models of noise, such as iid depolarising noise. We consider generalising these techniques for analysing codes under more realistic noise models, including features such as biased or correlated errors. We also consider designing customised codes which not only take into account and exploit features of the underlying physical noise. Considering such tailored codes will be of particular importance for NISQ applications in which finite-size effects can be significant. In Part II we apply tools from information theory to study the finite-resource effects which arise in the trade-offs between resource costs and error rates for certain quantum information processing tasks. We start by considering classical communication over quantum channels, providing a refined analysis of the trade-off between communication rate and error in the regime of a finite number of channel uses. We then extend these techniques to the problem of resource interconversion in theories such as quantum entanglement and quantum thermodynamics, studying finite-size effects which arise in resource-error trade-offs. By studying this effect in detail, we also show how detrimental finite-size effects in devices such as thermal engines may be greatly suppressed by carefully engineering the underlying resource interconversion processes.
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Santagati. "Towards quantum information processing in silicon quantum photonics." Thesis, University of Bristol, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.691181.
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After Feynman's proposal, in 1982, to simulate quantum systems using quantum computers, much effort has been focused on the study and realisation of machines capable of harnessing the power of quantum mechanics for simulation and computation. Many difFerent implementations have been proposed for the realisation of quantum technologies, all with their advantages and disadvantages. Integrated silicon photonics recently emerged as a promising approach: in fact all the necessary components for quantum computation can be integrated together on a silicon chip. In addition, the information carriers (photons) have very long coherence times and can be manipulated in an intrinsically phase-stable manner. The realisation of quantum photonic technologies is tied to the existence of a high efficiency single photon source (ideally on-demand). One of the possible solutions is in the multiplexing of many probabilistic photon pair sources. In this thesis we present four different quantum photonics experiments. We show the integration in a silicon quantum photonics platform of fundamental components for the implementation of any quantum information processing. We show that with our approach we can obtain high fidelity quantum states and high levels of entanglement. Furthermore, we also demonstrate the implementation of a hybrid (time and space) multiplexed single photon source in bulk optics.
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Ferrigno, Andrea Ann. "Processing information." Thesis, University of Iowa, 2013. https://ir.uiowa.edu/etd/2491.
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Lim, Yuan Liang. "Quantum information processing with single photons." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423321.
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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.
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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.
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Weinstein, Yaakov Shmuel 1974. "Experimental implementations of quantum information processing." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/88834.
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Childs, Andrew MacGregor 1977. "Quantum information processing in continuous time." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/16663.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2004.Includes bibliographical references (p. 127-138) and index.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Quantum mechanical computers can solve certain problems asymptotically faster than any classical computing device. Several fast quantum algorithms are known, but the nature of quantum speedup is not well understood, and inventing new quantum algorithms seems to be difficult. In this thesis, we explore two approaches to designing quantum algorithms based on continuous-time Hamiltonian dynamics. In quantum computation by adiabatic evolution, the computer is prepared in the known ground state of a simple Hamiltonian, which is slowly modified so that its ground state encodes the solution to a problem. We argue that this approach should be inherently robust against low-temperature thermal noise and certain control errors, and we support this claim using simulations. We then show that any adiabatic algorithm can be implemented in a different way, using only a sequence of measurements of the Hamiltonian. We illustrate how this approach can achieve quadratic speedup for the unstructured search problem. We also demonstrate two examples of quantum speedup by quantum walk, a quantum mechanical analog of random walk. First, we consider the problem of searching a region of space for a marked item. Whereas a classical algorithm for this problem requires time proportional to the number of items regardless of the geometry, we show that a simple quantum walk algorithm can find the marked item quadratically faster for a lattice of dimension greater than four, and almost quadratically faster for a four-dimensional lattice. We also show that by endowing the walk with spin degrees of freedom, the critical dimension can be lowered to two. Second, we construct an oracular problem that a quantum walk can solve exponentially faster than any classical algorithm.
(cont.) This constitutes the only known example of exponential quantum speedup not based on the quantum Fourier transform. Finally, we consider bipartite Hamiltonians as a model of quantum channels and study their ability to process information given perfect local control. We show that any interaction can simulate any other at a nonzero rate, and that tensor product Hamiltonians can simulate each other reversibly. We also calculate the optimal asymptotic rate at which certain Hamiltonians can generate entanglement.
by Andrew MacGregor Childs.
Ph.D.
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Garcia, Coello J. L. "Quantum information processing in mesoscopic systems." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1370589/.
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This thesis discusses various schemes and protocols for quantum information processing in mesoscopic systems with particular focus on using the spin of a particle as the bearer of information. The first chapter introduce various aspects of the field of quantum information used in this thesis such as qubits, entanglement, its quantification, quantum logic gates and entanglement swapping. In this chapter concepts such as AKLT states, decoherence and adiabatic elimination are introduced as they will be relevant in the thesis. In chapter 2 we introduce the Quantum Dots as the solid state system that will primarily be used as the hardware for the development of Quantum Information Processing (QIP). The different properties of quantum dots depending on their size are discussed. The exchange interaction between tunnel coupled quantum dots and the background of quantum computation in quantum dots is described. The principal sources of decoherence and the measurement techniques for spin qubits are presented. In chapter 3, carbon nanowires filled with N@C60 dimers are studied to analyse the entanglement between nuclear spins. The dimer is modelled as a two coupled nuclear spin- electron spin pair with a Heisenberg interaction. The entanglement have been studied depending on the temperature and the intensity of an external magnetic field. Witnessing the entanglement, and particularly bound entanglement are discussed. In chapter 4, the way to extract a singlet from a quantum dot is explored. The system that we model will be consisting of a triple dot and analyse the best way to get the singlet out, with each electron in a separate dot. The chief motivation is to create a singlet between separate dots in a time-scale much faster than that given by spinspin exchange interactions. In chapter 5, quantum logic gates in a triple dot system has been studied. Such gates have been widely studied in double and single quantum dots. Motivated by the advent of experimental set ups of triple dots, we have studied the natural quantum gates that came out of a triple dot system. There are still two spin quantum bits in the three dots and there is an empty intervening dot, which imparts the scheme some advantages, as well as a substantial difference from the class of schemes studied so far. In chapter 6, we model a large square dot. As we describe in chapter 2, the properties of the large dots make them behave with some interesting properties such as hosting Wigner molecules of electrons inside. We explore the application of these structures for quantum information processing. We show here how to get singlet/triplet measurement, entanglement swapping, and how to prepare a 1D AKLT state, using the square dot as a construction block of the system. Finally in chapter 7 conclusions and further work. Here we indicate the further work that could be done with the knowledge present in this thesis and motivated by future advances in the technology.
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Nock, Michael. "Single photons for quantum information processing." [S.l. : s.n.], 2006. http://nbn-resolving.de/urn:nbn:de:bsz:352-opus-21067.
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Daftuar, Sumit Kumar Preskill John P. "Eigenvalue inequalities in quantum information processing /." Diss., Pasadena, Calif. : California Institute of Technology, 2004. http://resolver.caltech.edu/CaltechETD:etd-03312004-100014.
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Busch, Jonathan. "Reservoir engineering for quantum information processing." Thesis, University of Leeds, 2010. http://etheses.whiterose.ac.uk/1365/.
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This thesis concerns possible implementations of quantum computing schemes and tries to overcome some standard limitations. The central result is a technique we call reservoir engineering that is applied to optical cavity QED based quantum computing. The usual problem for quantum computing with atomic qubits in cavities is scalability as this requires either the coupling of photons leaking from cavities,using linear optics elements and measurements or shuttling of ions into and out of cavities. We propose an alternative that applies strong dissipative coupling to an environment as a control on fibre-coupled cavity systems. The control mechanism is effectively an overdamping of certain common cavity modes that restricts the time evolution of the qubit-cavity system onto a smaller subsystem consisting of only one common cavity modes. Within this subsystem, we then show that it is possible to implement quantum computing schemes that apply otherwise only to atomic qubits in the same cavity.
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Gollub, Caroline. "Femtosecond quantum control studies on vibrational quantum information processing." Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-96201.
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Helmer, Ferdinand. "Quantum information processing and measurement in circuit quantum electrodynamics." Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-102919.
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Yang, Kaiyu, and 楊開宇. "Quantum information processing with quantum dots and Josephson junctions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B29285835.
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Del, Duce A. "Quantum Logic circuits for solid-state quantum information processing." Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/20166/.
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This thesis describes research on the design of quantum logic circuits suitable for the experimental demonstration of a three-qubit quantum computation prototype. The design is based on a proposal for optically controlled, solid-state quantum logic gates. In this proposal, typically referred to as SFG model, the qubits are stored in the electron spin of donors in a solid-state substrate while the interactions between them are mediated through the optical excitation of control particles placed in their proximity. After a brief introduction to the area of quantum information processing, the basics of quantum information theory required for the understanding of the thesis work are introduced. Then, the literature on existing quantum computation proposals and experimental implementations of quantum computational systems is analysed to identify the main challenges of experimental quantum computation and typical system parameters of quantum computation prototypes. The details of the SFG model are subsequently described and the entangling characteristics of SFG two-qubit quantum gates are analysed by means of a geometrical approach, in order to understand what entangling gates would be available when designing circuits based on this proposal. Two numerical tools have been developed in the course of the research. These are a quantum logic simulator and an automated quantum circuit design algorithm based on a genetic programming approach. Both of these are used to design quantum logic circuits compatible with the SFG model for a three-qubit Deutsch-Jozsa algorithm. One of the design aims is to realise the shortest possible circuits in order to reduce the possibility of errors accumulating during computation, and different design procedures which have been tested are presented. The tolerance to perturbations of one of the designed circuits is then analysed by evaluating its performance under increasing fluctuations on some of the parameters relevant in the dynamics of SFG gates. Because interactions in SFG two-qubit quantum gates are mediated by the optical excitation of the control particles, the solutions for the generation of the optical control signal required for the proposed quantum circuits are discussed. Finally, the conclusions of this work are presented and areas for further research are identified.
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Loukopoulos, Klearchos. "Multi-partite entanglement in quantum information processing." Thesis, University of Oxford, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.559825.
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Quantum theories have had an unprecedented success in providing a framework for studying physical systems. A fundamental implication of these theories is the existence of so-called entangled states, that is states whose description cannot be reduced to their constituents. These states are purely quantum and there is no such analogue in classical physics, where knowing the state of every particle is sufficient to infer the state of the system they compose. Entanglement is a core element of many quantum algorithms, quantum teleportation, quantum communications and quantum cryptographic scenarios. Furthermore, entanglement is present in nearly all solid-state systems, when they are at, or close to, their state of lowest energy. Therefore, it is both a technological resource and also a property which needs to be investigated in order to achieve understanding of real world materials at a fundamental level. The most concise demonstration of entanglement is perhaps in the case of maximal entanglement between two spin-l/2 particles. These maximally entangled two- particle states are called Bell states and they have been used to demonstrate experimentally that quantum mechanics is inequivalent to classical mechanics. A gen- eralization of this setting comes from studying entanglement between two physical systems, these can be either pure or mixed (e.g. in contact with a thermal bath). Entanglement between two systems, also knows as bipartite entanglement, has been studied in depth and quantified through various measures. However bipartite entanglement, by definition, is not the only quantity of in- terest. In some cases, entanglement is global and its properties cannot be reduced to studying bi-partitions. This type of entanglement, so-called multipartite entanglement, is harder to quantify and to study in general. Its presence is profound in physical systems that are at the point of undergoing a quantum phase transition and it is also a core ingredient for quantum error correcting codes, performing classical computation with quantum resources and some cryptographic scenarios. In this thesis we study properties of systems with multi-partite entanglement in the context of renormalization and quantum phase transitions, we show that multi- partite entanglement can be used to perform cryptographic tasks and we investigate what classes of Hamiltonians generate multiartite entanglement, while at the same time, their action can be simulated efficiently by a classical computer.
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Guha, Majumdar Mrittunjoy. "Quantum information processing using the power-of-SWAP." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/288005.
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This project is a comprehensive investigation into the application of the exchange interaction, particularly with the realization of the SWAP^1/n quantum operator, in quantum information processing. We study the generation, characterization and application of entanglement in such systems. Given the non-commutativity of neighbouring SWAP^1/n gates, the mathematical study of combinations of these gates is an interesting avenue of research that we have explored, though due to the exponential scaling of the complexity of the problem with the number of qubits in the system, numerical techniques, though good for few-qubit systems, are found to be inefficient for this research problem when we look at systems with higher number of qubits. Since the group of SWAP^1/n operators is found to be isomorphic to the symmetric group Sn, we employ group-theoretic methods to find the relevant invariant subspaces and associated vector-states. Some interesting patterns of states are found including onedimensional invariant subspaces spanned by W-states and the Hamming-weight preserving symmetry of the vectors spanning the various invariant subspaces. We also devise new ways of characterizing entanglement and approach the separability problem by looking at permutation symmetries of subsystems of quantum states. This idea is found to form a bridge with the entanglement characterization tool of Peres-Horodecki's Partial Positive Transpose (PPT), for mixed quantum states. We also look at quantum information taskoriented 'distance' measures of entanglement, besides devising a new entanglement witness in the 'engle'. In terms of applications, we define five different formalisms for quantum computing: the circuit-based model, the encoded qubit model, the cluster-state model, functional quantum computation and the qudit-based model. Later in the thesis, we explore the idea of quantum computing based on decoherence-free subspaces. We also investigate ways of applying the SWAP^1/n in entanglement swapping for quantum repeaters, quantum communication protocols and quantum memory.
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Zhang, Qinghua. "Quantum information processing with a geometric scenario." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/HKUTO/record/B39557613.
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Zhang, Qinghua, and 張清華. "Quantum information processing with a geometric scenario." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39557613.
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Jarratt, Marie Claire. "Readout and Control: Scalable Techniques for Quantum Information Processing." Thesis, The University of Sydney, 2019. https://hdl.handle.net/2123/21572.
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Quantum mechanics allows for the processing of information in entirely new ways, surpassing the computational limits set by classical physics. Termed `quantum information processing', scaling this scheme relies on simultaneously increasing the number of qubits -- the fundamental unit of quantum computation -- whilst reducing their error rates. With this comes a variety of challenges, including the ability to readout the quantum state of large numbers of qubits, as well as to control their evolution in order to mitigate errors. This thesis aims to address these challenges by developing techniques for the readout and control of quantum systems. The first series of experiments focuses on the readout of GaAs/AlGaAs semiconductor quantum systems, primarily relating to the technique of dispersive gate sensing (DGS). DGS is used to probe electron transmission in an open system, a quantum point contact, demonstrating an ability to resolve characteristic features of a one-dimensional ballistic channel in the limit where transport is not possible. DGS is also used to observe anomalous signals in the potential landscape of quantum-dot defining gate electrodes. A technique for time domain multiplexing is also presented, which allows for readout resources, in the form of microwave components, to be shared between multiple qubits, increasing the capacity of a single readout line. The second series of experiments validates control techniques using trapped 171Yb+ ions. Classical error models are engineered using high-bandwidth IQ modulation of the microwave source used to drive qubit rotations. Reductions in the coherent lifetime of the quantum system are shown to match well with quantitative models. This segues in to developing techniques to understand and suppress noise in the system. This is achieved using the filter-transfer function approach, which casts arbitrary quantum control operations on qubits as noise spectral filters.
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Gütschow, Johannes [Verfasser]. "Quantum information processing with Clifford quantum cellular automata / Johannes Gütschow." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2013. http://d-nb.info/1033705470/34.
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Anwar, Muhammad Sabieh. "NMR quantum information processing with para-hydrogen." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410620.
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Cummins, Holly Katherine. "Quantum information processing and nuclear magnetic resonance." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393477.
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Jones, Mark Alexander Goddard. "Luminescent erbium metallofullerenes for quantum information processing." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437365.
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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] .
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Jeong, H. "Quantum information processing with non-classical light." Thesis, Queen's University Belfast, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398097.
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Cappellaro, Paola. "Quantum information processing in multi-spin systems." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/41282.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2006.Includes bibliographical references (p. 133-142).
Coherence and entanglement in multi-spin systems are valuable resources for quantum information processing. In this thesis, I explore the manipulation of quantum information in complex multi-spin systems, with particular reference to Nuclear Magnetic Resonance implementations. In systems with a few spins, such as molecules in the liquid phase, the use of multi-spin coherent states provides a hedge against the noise, via the encoding of information in logical degrees of freedom distributed over several spins. Manipulating multi-spin coherent states also increases the complexity of quantum operations required in a quantum processor. Here I present schemes to mitigate this problem, both in the state initialization, with particular attention to bulk ensemble quantum information processing, and in the coherent control and gate implementations. In the many-body limit provided by nuclear spins in single crystals, the limitations in the available control increase the complexity of manipulating the system; also, the equations of motion are no longer exactly solvable even in the closed-system limit. Entanglement and multi-spin coherences are essential for extending the control and the accessible information on the system. I employ entanglement in a large ensemble of spins in order to obtain an amplification of the small perturbation created by a single spin on the spin ensemble, in a scheme for the measurement of a single nuclear spin state. I furthermore use multiple quantum coherences in mixed multi-spin states as a tool to explore many-body behavior of linear chain of spins, showing their ability to perform quantum information processing tasks such as simulations and transport of information.
(cont.) The theoretical and experimental results of this thesis suggest that although coherent multi-spin states are particularly fragile and complex to control they could make possible the execution of quantum information processing tasks that have no classical counterparts.
by Paola Cappellaro.
Ph.D.
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Pant, Mihir. "Architectures for photon-mediated quantum information processing." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115766.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 173-186).
In this thesis, I present architectures for quantum information processing where photons are used as the quantum bit (qubit) or for mediating entanglement between other qubits. The emphasis of this research is to simplify the basic building blocks required in such processors. The all-photonic repeater and computing architectures do not require material nonlinearities, and their resource requirements are reduced by several orders of magnitude. The photon-mediated atomic memory architecture is designed to work with faulty memories and experimentally demonstrated values of coherence time and photonic coupling efficiency. In the quantum network architecture, the only operation at every node is probabilistic Bell measurement.
by Mihir Pant.
Ph. D.
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Leedumrongwatthanakun, Saroch. "Quantum information processing with a multimode fibre." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS526.
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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
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Santamato, Alberto. "Quantum information processing with integrated photonic materials." Thesis, University of Bristol, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.707742.
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Canale, Matteo. "Classical processing algorithms for Quantum Information Security." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3423585.
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In this thesis, we investigate how the combination of quantum physics and information theory could deliver solutions at the forefront of information security, and, in particular, we consider two focus applications: randomness extraction as applied to quantum random number generators and classical processing algorithms for quantum key distribution (QKD).
We concentrate on practical applications for such tools.
We detail the implementation of a randomness extractor for a commercial quantum random number generator, and we evaluate its performance based on information theory.
Then, we focus on QKD as applied to a specific experimental scenario, that is, the one of free-space quantum links. Commercial solutions with quantum links operating over optical fibers, in fact, already exist, but suffer from severe infrastructure complexity and cost overheads. Free-space QKD allows for a higher flexibility, for both terrestrial and satellite links, whilst experiencing higher attenuation and noise at the receiver. In this work, its feasibility is investigated and proven in multiple experiments over links of different length, and in various channel conditions. In particular, after a thorough analysis of information reconciliation protocols, we consider finite-key effects as applied to key distillation, and we propose a novel adaptive real-time selection algorithm which, by leveraging the turbulence of the channel as a resource, extends the feasibility of QKD to new noise thresholds.
By using a full-fledged software for classical processing tailored for the considered application scenario, the obtained results are analyzed and validated, showing that quantum information security can be ensured in realistic conditions with free-space quantum links.In questa tesi si mostra come la combinazione tra la fisica quantistica e la teoria dell'informazione permetta di realizzare protocolli all'avanguardia per la sicurezza dell'informazione. Si considerano in particolare due specifiche applicazioni: la randomness extraction per generatori quantistici di numeri casuali e gli algoritmi di processing classici nel contesto della crittografia quantistica. Focalizzando lo studio sugli sviluppi pratici delle menzionate applicazioni, si descrive anzitutto in dettaglio l'implementazione di un randomness extractor per un generatore quantistico di numeri casuali ad uso commerciale, e si valutano le sue prestazioni sulla base della teoria dell'informazione. Quindi, ci si concentra sulla crittografia quantistica nello specifico scenario sperimentale dei canali quantistici in spazio libero. Ad oggi, infatti, sono disponibili soluzioni commerciali con canali quantistici in fibra ottica, che sono però condizionate da un'alta complessità infrastrutturale e da un elevato costo economico. La crittografia quantistica in spazio libero, al contrario, permette una maggior flessibilità, sia per link terrestri che per link satellitari, nonostante essa soffra di perdite e rumore più elevati al ricevitore. Attraverso la realizzazione di vari esperimenti su link di diversa lunghezza e con diverse condizioni di canale, se ne dimostra la fattibilità. In particolare, dopo un'accurata analisi dei protocolli di correzione d'errore, si considerano gli effetti della lunghezza finita delle chiavi sul processo di distillazione. Inoltre, si propone un algoritmo innovativo di selezione adattiva ed in tempo reale dei dati che, sfruttando la turbolenza del canale come risorsa, permette di estendere l'applicabilità della crittografia quantistica a nuovi livelli di rumore. Utilizzando un software per il processing classico ottimizzato per lo scenario considerato, i risultati ottenuti sono quindi analizzati e validati, dimostrando che la sicurezza quantistica dell'informazione può essere garantita in condizioni realistiche con link quantistici in spazio libero. %In questa tesi, si studia come la combinazione della fisica quantistica e della teoria dell'informazione permettano di realizzare protocolli all'avanguardia per la sicurezza dell'informazione. In particolare, si considerano due specifiche applicazioni: l'estrazione di casualità per generatori quantistici di numeri casuali e gli algoritmi classici di processing nel contesto della crittografia quantistica. Mentre il primo strumento consente di dimostrare l'uniformità delle sequenze casuali prodotte, i secondi permettono di creare un sistema per lo scambio di chiavi incondizionatamente sicure. %Focalizziamo lo studio sulle applicazioni pratiche di questi strumenti. Descriviamo in dettaglio l'implementazione di un estrattore di casualità per un generatore quantistico di numeri casuali commerciale, e valutiamo le sue prestazioni basandoci sulla teoria dell'informazione. Quindi, ci concentriamo sulla crittografia quantistica nello specifico scenario sperimentale dei canali quantistici in spazio libero. Ad oggi, infatti, sono già disponibili soluzioni commerciali con canali quantistici in fibra ottica, che sono però condizionate da un'alta complessità infrastrutturale e da un elevato costo economico. D'altro canto, la crittografia quantistica in spazio libero permette una maggiore flessibilità, sia per link terrestri che per link satellitari, ma soffre di perdite e rumore più elevati al ricevitore. In questo lavoro, studiamo le sue applicazioni e ne dimostriamo la fattibilità in vari esperimenti, su link di diversa lunghezza e con diverse condizioni di canale. In particolare, dopo un'accurata analisi dei protocolli di correzione d'errore, consideriamo gli effetti dell'analisi alle chiavi finite sul processo di distillazione della chiave e proponiamo un algoritmo innovativo di selezione adattiva ed in tempo reale dei dati che, sfruttando la turbolenza del canale come risorsa, permette di estendere l'applicabilità della crittografia quantistica a nuovi livelli di rumore. Utilizzando un complesso software per il processing classico ottimizzato per lo scenario considerato, i risultati ottenuti sono analizzati e validati, dimostrando che la sicurezza quantistica dell'informazione può essere garantita in condizioni realistiche con link quantistici in spazio libero.
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Shaikh, Fayaz A. "Monolithic microfabricated ion trap for quantum information processing." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47597.
Full textAbstract:
The objective of this research is to design, fabricate, and demonstrate a microfabricated
monolithic ion trap for applications in quantum computation and quantum simulation.
Most current microfabricated ion trap designs are based on planar-segmented surface electrodes.
Although promising scalability to trap arrays containing ten to one hundred ions,
these planar designs suffer from the challenges of shallow trap depths, radial asymmetry of
the confining potential, and electrode charging resulting from laser interactions with dielectric
surfaces. In this research, the design, fabrication, and testing of a monolithic
and symmetric two-level ion trap is presented. This ion trap overcomes the challenges of
surface-electrode ion traps. Numerical electrostatic simulations show that this symmetric
trap produces a deep (1 eV for 171Yb+ ion), radially symmetric RF confinement potential.
The trap has an angled through-chip slot that allows back-side ion loading and generous
through laser access, while avoiding surface-light scattering and dielectric charging that
can corrupt the design control electrode compensating potentials. The geometry of the trap
and its dimensions are optimized for trapping long and linear ion chains with equal spacing
for use with quantum simulation problems and quantum computation architectures.
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Tame, Mark Simon. "Measurement-based quantum information processing with imperfect operation." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486208.
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Recently, there has. been considerable interest from the quantum information community in a new approach to quantum information processing (QIP) known as the measurement-based (MB) model. The model is based on the use of measurements to manipulate entanglement (quantum correlations) shared' between the elements of multipartite quantum systems in order to carry out processing tasks, such as quantum computation (QC). This Thesis addresses the MB model and its practical operation when imperfections are present. The imperfections consider~d are ip the form of intrinsic systematic noise, natural limitations in the structure of the quantum resources and environment-induced decoherence in a variety of experim~ntalsetups.
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Langer, Christopher E. "High fidelity quantum information processing with trapped ions." Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3219011.
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Gines, Laia. "Nanodiamond single photon sources for quantum information processing." Thesis, Cardiff University, 2018. http://orca.cf.ac.uk/117302/.
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This thesis is focused on the production and characterization of diamond films and diamond nanoparticles containing custom colour centres. These defects intentionally created into the diamond lattice are promising candidates for single photon sources, and are becoming more important for quantum information technologies as photons can carry quantum information over long distances. With outstanding properties such as up to 80% of the photons emitted into the zero phonon line (ZPL), single photon count rates up to several Mcps under continuous excitation and a narrow ZPL at room temperature, the SiV centre has recently attracted more attention. Although different approaches for the creation of colour centres have been reported, this thesis details the creation of SiV centres by chemical vapour deposition. Colour centres are created through the incorporation of impurities during diamond growth. While Si doping can easily be achieved due to plasma etching of Si substrates or the incorporation of a Si solid source inside the reactor vacuum chamber, controlling the exact amount of Si present in the gas phase or effectively incorporated is still a handicap. Chapters five and six show comprehensive studies performed towards the creation of diamond nanoparticles with single emitters. Control over the Si content within the gas phase is achieved using silane as gas source. The subsequent milling of the diamond films hosting the SiV centres and their inclusion into a stable solution, will facilitate SiV coupling and incorporation into cavities or emission-enhancer devices.
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Karamlou, Amir H. "Towards quantum information processing with diamond color centers." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119749.
Full textAbstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 59-63).
The DiVincenco requirements summarize the key properties that quantum systems should have to be useful for quantum computing. The work in this thesis focuses on one of the leading solid-state quantum systems, the nitrogen vacancy (NV) center in diamond. The NV has emerged as an excellent quantum sensor, in which quantum logic techniques can significantly improve performance. However, a remaining problem concerns the rate and fidelity of NV spin measurement. To address this problem in this thesis we first propose and theoretically demonstrate a scheme for spatially robust state-selective transitions with over 99.9% fidelity between different spin states in zero-field splitting. Furthermore, another central challenge tackled in this work is the efficient collection of the emitter's fluorescence. Optical antennas are appealing as they offer directional emission together with spontaneous emission rate enhancement across a broad emitter spectrum. We introduce and optimize metal-dielectric nano-antenna designs recessed into a diamond substrate and aligned with quantum emitters. We analyze trade-offs between external quantum efficiency, collection efficiency, Purcell factor, and overall collected photon rate. This analysis shows that an optimized metal-dielectric hybrid structure can increase the collected photon rate from a nitrogen vacancy center by over two orders of magnitude compared to a bare emitter. As a result, these metal-dielectric antennas should enable single-shot electron spin measurements of NV centers at room temperature.
by Amir H. Karamlou.
M. Eng.
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Warner, M. "Beyond classical computing : towards organic quantum information processing." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1334690/.
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This thesis examines the potential of a class of organic molecules, porphyrin derivatives, for quantum information purposes. The experiments in this thesis follow a simple progression: they begin by exploring the time-independent characteristics of the molecules, then investigate the dynamics and decoherence, and end with a consideration of the potential for controllable coupling. Whilst this methodology is obviously motivated by interest in quantum information processing (QIP), it is hoped that the results will have relevance for a larger group of fields including organic electronics, solar energy and spintronics. QIP is at the forefront of science, requiring an understanding of the coherent properties of materials - an understanding deeper than has ever been required before. Since copper phthalocyanine is a technologically relevant material, with uses in organic electronics and solar cells, and possible applications in the developing field of spintronics, this deep understanding can be fed back to provide interesting new developments. The first experimental chapter, Chapter 4, is such an example, where work focussed on understanding a novel phase of CuPc (the \eta-phase), through magnetometry and electron spin resonance led to the development of a method to measure the magnetic properties of liquids. It is hoped that this could open a path for solution based biological samples to be studied via magnetometry. A discussion of the details of the technique, the interpretation of the data, and a proof of principle are provided in this chapter. Another interesting technological development is discussed in Chapter 5, where the initial characterisation of the thin films of copper phthalocyanine (CuPc) led to a deeper understanding of their nanostructure, an important property for the development of solar cells. This consisted of continuous wave electron spin resonance (ESR) experiments on thin films of CuPc, varying both the percentage of copper and the orientation of the molecules, to allow the interpretation of the ESR spectra of mixed films of CuPc and C60, the mixture that is used in organic solar cells. I demonstrate that the CuPc and C60 form nano-clusters in these films, with a preferred orientation. Since the mixed films are known to be more efficient than a simple two layer device, this result provides new information, which can be used to improve the design of this type of solar cell. Chapter 6 consists of the measurement of the decoherence times of spins in CuPc films, and an understanding of the mechanisms of decoherence. Pulsed ESR is used on both powders and thin films of copper phthalocyanine and the field and temperature dependence is explored. Since it is unlikely that molecules in solution will ever be able to provide a scalable QIP solution, this move to the solid state represents a real advance. It is not trivial however, as the solid state can provide many additional decoherence routes. These times are the first step in proposing a material as a potential vehicle for QIP, and I demonstrate that the decoherence times are long enough that, given its other advantages, CuPc can be taken seriously as a candidate host for qubits. The important distinction of these measurements from those that have been made before on, for instance, molecular magnets is that these decoherence times are achieved in the solid state. The last results chapter is an attempt to make progress on a problem that is particularly relevant for molecular QIP. Since molecules can be made easily, they provide a attractive path to an individual qubit. The identical nature of the molecules comes at a price, though, as it makes it hard to address each qubit independently. Chapter 7 seeks to explore the physics of optically coupling two qubits (in this case TEMPO radicals) through a porphyrin linker. Steady state and time resolved optical absorption and pulsed and transient ESR are used to characterise the spin physics of the samples. I demonstrate that it is very likely a coupling can be controllably switched on (if not, as yet, o). This chapter lays the foundations for a considerable number of future experiments, some of which are discussed at the end, that could demonstrate a truly switchable coherent coupling between qubits.
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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.
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Carthy, Laura. "Linking Wheels for use in quantum information processing." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/linking-wheels-for-use-in-quantum-information-processing(ca5addcd-5ce1-4e9d-86f5-e56405a4092c).html.
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Heterometallic Cr7Ni-containing wheels have been identified as potential qubits for use in quantum information processing. The work described in this thesis details attempts to form a variety of multi-qubit systems for the purposes of better understanding the interactions occurring between the wheels and also forming potential 2-qubit quantum gates using redox/photo-active links. Mono-substituted wheels of type [Pr2NH2][Cr7MF8(O2CCMe3)15(L)], where L is acarboxylate with a pendant coordinating group, have been synthesised for use as bulky ligands in coordination chemistry with metal complexes. Various carboxylates have been substituted into the wheels and the products reacted with first row transition metal complexes in order to extend the series of linked-wheel systems. Many of these novel complexes have been characterised by X-ray crystallography, and in certain cases EPR studies have been undertaken to probe the strength of interactions occurring via different bridging units. The first well-established substituted wheel, [Pr2NH2][Cr7NiF8(O2CCMe3)15(O2CPy)] (Py= pyridine), has also been used in reactions with second and third row transition metal centres to show its ability to act as a ligand under more harsh conditions. In addition, the disubstituted product [Pr2NH2][Cr7NiF8(O2CCMe3)14(O2CPy)2] has been reacted with a copper complex in order to form a polymeric structure. Purple wheels of type [Cr7NiF3(O2CCMe3)15(EtGu)(H2O)] have been linked through a variety of extended organic molecules containing a minimum of two pendent pyridyl groups. Use of a ligand containing four pyridyl groups, 2,2´:4,4´´:4´,4´´´-quaterpyridyl(qpy) produced a three-wheel-containing system, creating an interesting modification of the wheel backbone not seen before. A series of transition metal complexes, containing qpy and its extended derivative bbpe, has been synthesised in order to form linked-wheel systems. While none of these systems has to date yielded a crystal structure, a significant amount of evidence has been collected to confirm successful formation of the desired products. UV-vis spectroscopic and electrochemical measurements show that these compounds are photo and/or redox-active,and preliminary luminescence studies indicate that the presence of the wheels quenches the emission from metal-to-ligand charge-transfer excited states. A series of mixed-wheel systems has been synthesised by reacting four different monosubstituted green wheels with four purple wheels (Cr7M, where M = Ni, Co, Mn or Zn). A total of fourteen novel systems has been formed, with two of the attempted reactions failing to occur. EPR studies on Cr7Ni-Cr7Ni linked systems show that the strongest interaction occurs when using isonicotinate as a link, with 4-pyridazinecarboxylate giving the weakest coupling. Studies have also been undertaken on Cr7Ni-Cr7Mn and Cr7Ni-Cr7Zn systems, with the former showing interactions and the latter showing none. Initial work to link wheels together indirectly via their templates was ultimately unsuccessful, but a variety of potential linker molecules were synthesised and are described.
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Britton, Joe. "Microfabrication techniques for trapped ion quantum information processing." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3337078.
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Englund, Dirk. "Photonic crystals for quantum and classical information processing /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Kirkwood, Robert A. "Superconducting single photon detectors for quantum information processing." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8136/.
Full textAbstract:
Single photon detectors are a vital part of many emerging technologies which harness the quantum properties of light to benefit the fields of communication, computation and sensing. Superconducting nanowire single photon detectors (SNSPDs) offer high detection efficiency, low dark count rates, low timing jitter, and infrared sensitivity that are required by the most demanding single photon counting applications. This thesis presents SNSPDs fabricated and tested at the University of Glasgow that are integrated with optical structures which enable enhanced detection efficiency and integration with waveguide circuit technology. The monolithic integration of waveguide circuit components presents a route towards realisation of an optical quantum information processor that has the stability and scalability to perform the demanding tasks of quantum computation. A novel process is introduced for incorporating superconducting detectors with single mode gallium arsenide waveguides and quantum dot single photon sources. Together these elements would enable the generation of quantum states of light which could be manipulated and detected on a single chip. Detectors are patterned in NbTiN thin superconducting films on to suspended nanobeam waveguides with better than 50 nm alignment accuracy. Low temperature electrical and optical testing confirms the detectors’ single photon sensitivity under direct illumination as well as to waveguide coupled light. Measured detectors were found to have internal registering efficiencies of 6.8 ± 2.4%. Enhancing absorption of photons into thin superconducting films is vital to the creation of high efficiency superconducting single photon detectors. Fabricating an SNSPD on a dielectric mirror creates a partial cavity that can be tailored to enhance detection of light at specific wavelengths. Devices have been fabricated and tested in this thesis with enhanced detection efficiency at infrared and visible wavelengths for quantum cryptography, remote sensing and life science applications. Detectors fabricated in NbTiN on GaAs/AlGaAs Bragg mirrors exhibited a system detection efficiency of 1.5% at 1500 nm wavelength for the best device measured. SNSPDs were also fabricated in NbN on aperiodic dielectric mirrors with a range of different bandwidths. A peak system detection efficiency of 82.7% at 808 nm wavelength was recorded.