Dissertations / Theses on the topic 'Quantum Processing'
To see the other types of publications on this topic, follow the link: Quantum Processing.
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 Processing.'
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
Eldar, Yonina Chana 1973. "Quantum signal processing." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/16805.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2002.Includes bibliographical references (p. 337-346).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Quantum signal processing (QSP) as formulated in this thesis, borrows from the formalism and principles of quantum mechanics and some of its interesting axioms and constraints, leading to a novel paradigm for signal processing with applications in areas ranging from frame theory, quantization and sampling methods to detection, parameter estimation, covariance shaping and multiuser wireless communication systems. The QSP framework is aimed at developing new or modifying existing signal processing algorithms by drawing a parallel between quantum mechanical measurements and signal processing algorithms, and by exploiting the rich mathematical structure of quantum mechanics, but not requiring a physical implementation based on quantum mechanics. This framework provides a unifying conceptual structure for a variety of traditional processing techniques, and a precise mathematical setting for developing generalizations and extensions of algorithms. Emulating the probabilistic nature of quantum mechanics in the QSP framework gives rise to probabilistic and randomized algorithms. As an example we introduce a probabilistic quantizer and derive its statistical properties. Exploiting the concept of generalized quantum measurements we develop frame-theoretical analogues of various quantum-mechanical concepts and results, as well as new classes of frames including oblique frame expansions, that are then applied to the development of a general framework for sampling in arbitrary spaces. Building upon the problem of optimal quantum measurement design, we develop and discuss applications of optimal methods that construct a set of vectors.
(cont.) We demonstrate that, even for problems without inherent inner product constraints, imposing such constraints in combination with least-squares inner product shaping leads to interesting processing techniques that often exhibit improved performance over traditional methods. In particular, we formulate a new viewpoint toward matched filter detection that leads to the notion of minimum mean-squared error covariance shaping. Using this concept we develop an effective linear estimator for the unknown parameters in a linear model, referred to as the covariance shaping least-squares estimator. Applying this estimator to a multiuser wireless setting, we derive an efficient covariance shaping multiuser receiver for suppressing interference in multiuser communication systems.
by Yonina Chana Eldar.
Ph.D.
2
Venegas-Andraca, Salvador Elías. "Discrete quantum walks and quantum image processing." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427612.
Full textAbstract:
In this thesis we have focused on two topics: Discrete Quantum Walks and Quantum Image Processing. Our work is a contribution within the field of quantum computation from the perspective of a computer scientist. With the purpose of finding new techniques to develop quantum algorithms, there has been an increasing interest in studying Quantum Walks, the quantum counterparts of classical random walks. Our work in quantum walks begins with a critical and comprehensive assessment of those elements of classical random walks and discrete quantum walks on undirected graphs relevant to algorithm development. We propose a model of discrete quantum walks on an infinite line using pairs of quantum coins under different degrees of entanglement, as well as quantum walkers in different initial state configurations, including superpositions of corresponding basis states. We have found that the probability distributions of such quantum walks have particular forms which are different from the probability distributions of classical random walks. Also, our numerical results show that the symmetry properties of quantum walks with entangled coins have a non-trivial relationship with corresponding initial states and evolution operators. In addition, we have studied the properties of the entanglement generated between walkers, in a family of discrete Hadamard quantum walks on an infinite line with one coin and two walkers. We have found that there is indeed a relation between the amount of entanglement available in each step of the quantum walk and the symmetry of the initial coin state. However, as we show with our numerical simulations, such a relation is not straightforward and, in fact, it can be counterintuitive. Quantum Image Processing is a blend of two fields: quantum computation and image processing. Our aim has been to promote cross-fertilisation and to explore how ideas from quantum computation could be used to develop image processing algorithms. Firstly, we propose methods for storing and retrieving images using non-entangled and entangled qubits. Secondly, we study a case in which 4 different values are randomly stored in a single qubit, and show that quantum mechanical properties can, in certain cases, allow better reproduction of original stored values compared with classical methods. Finally, we briefly note that entanglement may be used as a computational resource to perform hardware-based pattern recognition of geometrical shapes that would otherwise require classical hardware and software.
3
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.
Full text
4
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.
Full text
5
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.
Full textAbstract:
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.
6
Rossini, Davide. "Quantum information processing and Quantum spin systems." Doctoral thesis, Scuola Normale Superiore, 2007. http://hdl.handle.net/11384/85856.
Full text
7
Hutton, Alexander. "Networked quantum information processing." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403741.
Full text
8
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.
Full textAbstract:
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.
9
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
10
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.
11
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.
Full textAbstract:
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
12
Chubb, Christopher. "Noise in Quantum Information Processing." Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/20682.
Full textAbstract:
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.
13
Gollub, Caroline. "Femtosecond quantum control studies on vibrational quantum information processing." Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-96201.
Full text
14
Helmer, Ferdinand. "Quantum information processing and measurement in circuit quantum electrodynamics." Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-102919.
Full text
15
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.
Full text
16
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/.
Full textAbstract:
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.
17
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.
Full text
18
Chen, Joseph C. H. "Quantum computation and natural language processing." [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=965581020.
Full text
19
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.
Full text
20
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.
21
Weinstein, Yaakov Shmuel 1974. "Experimental implementations of quantum information processing." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/88834.
Full text
22
Childs, Andrew MacGregor 1977. "Quantum information processing in continuous time." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/16663.
Full textAbstract:
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.
23
Garcia, Coello J. L. "Quantum information processing in mesoscopic systems." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1370589/.
Full textAbstract:
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.
24
Nock, Michael. "Single photons for quantum information processing." [S.l. : s.n.], 2006. http://nbn-resolving.de/urn:nbn:de:bsz:352-opus-21067.
Full text
25
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.
Full text
26
Busch, Jonathan. "Reservoir engineering for quantum information processing." Thesis, University of Leeds, 2010. http://etheses.whiterose.ac.uk/1365/.
Full textAbstract:
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.
27
Jarratt, Marie Claire. "Readout and Control: Scalable Techniques for Quantum Information Processing." Thesis, The University of Sydney, 2019. https://hdl.handle.net/2123/21572.
Full textAbstract:
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.
28
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.
Full textAbstract:
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.
29
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.
Full textAbstract:
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.
30
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.
Full text
31
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.
Full text
32
Marguerite, Arthur. "Two-particle interferometry for quantum signal processing." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066124/document.
Full textAbstract:
Cette thèse est dédiée à l'analyse de signaux électriques quantiques dans les canaux de bords de l'effet Hall quantique. En particulier, j'ai utilisé l'analogue électronique de l'interféromètre de Hong, Ou et Mandel pour réaliser des expériences d'interférométrie à deux particules. En entrée de l'interféromètre sont placées des sources d'électrons uniques qui permettent l'injection contrôlée d'excitation ne contenant qu'une seule particule. Les canaux de bords guident ces excitations jusqu'à l'interféromètre. Il s'agit d'un contact ponctuel quantique qui agit comme une lame semi-réfléchissante pour les électrons. On mesure en sortie les fluctuations basse fréquence du courant. Cela nous permet de mesurer le recouvrement entre les fonctions d'onde à un électron émises à chaque entrée. Grâce à cette mesure de recouvrement, j'ai pu caractériser à des échelles de temps sub-nanoseconde, le rôle des interactions Coulombienne sur la propagation de l'électron unique. J'ai pu montrer que ces interactions étaient la source principale de la décohérence du paquet d'onde mono-électronique et qu'elles décomposent l'électron sur des modes collectifs. C'est une manifestation de la fractionalisation de l'électron qui apparaît dans les systèmes uni-dimensionnel en interactions. Grâce à cet interféromètre, j'ai pu aussi implémenter un protocole de tomographie qui permet de reconstruire toute les informations à une particule de n'importe quel signal émis dans le canal de bordThis thesis is dedicated to processing of quantum electronic signals in the edge channels of the integer quantum Hall effect. In particular, I used the electronic analogue of the Hong, Ou and Mandel interferometer to realize two particle interference measurements. The interferometer consists of a quantum point contact (QPC) that acts as an electronic beam-splitter. The inputs are fed by single electron sources whose single particle excitations are guided toward the QPC by quantum Hall edge channels. We measure low frequency current noise in one of the output to measure overlaps of first order coherence functions. With this interferometer I could characterize on short time scales the role of Coulomb interactions on single electron propagation. I could show that interactions are the main source of decoherence of the single particle wave packet and that the electron decomposes into collective modes. This is due to fractionalisation which is a hallmark of interacting unidimensional systems. Thanks to this interferometer I could also implement a universal tomography protocol to dissect all single particle information of any arbitrary current. This enables the study of non-classical propagating state
33
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.
Full text
34
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.
Full text
35
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.
Full text
36
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] .
37
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.
Full text
38
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.
39
Low, Guang Hao. "Quantum signal processing by single-qubit dynamics." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/115025.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 117-125).
Quantum computation is the most powerful realizable model of computation, and is uniquely positioned to solve specialized problems intractable to classical computers. This quantum advantage arises from directly exploiting the strangeness of quantum mechanics that is fundamental to reality. As such, one expects our understanding of quantum processes in physical systems to be indispensable to the design and execution of quantum algorithms. We present quantum signal processing, which exploits the dynamics of simple quantum systems to perform non-trivial computations. Such systems applied as computational modules in larger quantum algorithms, offer a natural physical alternative to standard tasks such as the calculation of elementary functions with integer arithmetic. The quantum advantage of this approach, based on simple physics, is of significant practical relevance. In cases, arbitrary bits of precision may be emulated using only constant space. Moreover, the simplicity and performance of quantum signal processing is such that it is the final missing ingredient for realizing a number of optimal quantum algorithms, particularly in Hamiltonian simulation. Quantum signal processing realizes a useful fusion of analog and digital models of quantum computation. At the physical level, we focus on how even a simple two-level system - the qubit, computes through optimal discrete-time quantum control. Whereas quantum control is typically used to synthesize unitary quantum gates, we solve the synthesis problem of unitary quantum functions with a fully characterization of achievable functions, and efficient techniques for their implementation. This furnishes a surprisingly rich framework in the analog model of quantum computation for computing functions. The generality of this model is realized by many applications, often with no modification, to quantum algorithms designed for digital quantum computers, in particular for matrix manipulation. In this manner, we solve a number of open problem related to optimal amplitude amplification algorithms, optimally computing on matrices with a quantum computer, and the simulation of physical systems.
by Guang Hao Low.
Ph. D.
40
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.
41
Rimmer, David. "A Bayesian approach to quantum signal processing." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614194.
Full text
42
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
43
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.
Full text
44
Canale, Matteo. "Classical processing algorithms for Quantum Information Security." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3423585.
Full textAbstract:
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.
45
Oshima, Toshio. "Quantum coherence in solid-states and its application to quantum information processing." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613264.
Full text
46
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.
47
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.
48
Mandarino, A. "QUANTUM PROBING AND CHARACTERIZATION TECHNIQUES FOR SYSTEMS OF INTEREST IN QUANTUM INFORMATION PROCESSING." Doctoral thesis, Università degli Studi di Milano, 2016. http://hdl.handle.net/2434/356925.
Full textAbstract:
The thread of this thesis is an attempt to clarify some assumptions that sound reasonable but whose correctness has never been proved or demonstrated formally. The first question I consider is: Do two quantum states near in the Hilbert space have the same, or almost the same, physical properties? First of all we have to clarify with which kind of measure we would like to measure the distance between two states. I do consider a measure, called Fidelity, that acts from the Hilbert space of a bipartite system to [0; 1]. Fidelity is null when the two states are orthogonal while if it is 1 the two states coincides.
I show that high fidelities may be achieved by pairs of states with considerably different physical properties, including separable and entangled states or classical and nonclassical ones. Therefore, fidelity alone cannot be used to asses the very quantum properties of two states,but a tomographic reconstruction of the state is required. Secondly I question: Does a good quantum thermometer could be build with a system showing phase transition? I employ a critical magnetic system, known as Lipkin-Meshkov-Glick model, I study it in contact with a reservoir with it has thermalized but whose temperature is an unknown temperature to be estimated. I show that the best precision for temperature estimation it is not at critical point as someone could suspect but nevertheless criticality is an unmatchable resource even in the quantum realm. Last question is: when two different probes spatially separated interact with a common or a separate bath? It is quite a common opinion that systems, two objects located far away one from each others, feel the effect of different environments. Dissipation and decoherence are the two main processes which a quantum system undergo when it is not isolated, but when it interacts with another system much bigger. I explore how two different systems put in contact with a common bath show decoherence with typical quantum interference leading to a non obvious definition of separate environments.
49
Ferrigno, Andrea Ann. "Processing information." Thesis, University of Iowa, 2013. https://ir.uiowa.edu/etd/2491.
Full text
50
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.
Full textAbstract:
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.