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作者： Sam Morley-Short University of Bristol

学位级别：博士

With the end of Moore's Law within sight, quantum computers offer a tantalising paradigm shift in computational power. Currently, many quanta are competing to realise such a revolutionary device, of which this thesis considers one in particular: linear optical quantum computation (LOQC). Over the past decade LOQC architectures have developed from "efficient" but unfeasible toy models to serious contenders. A significant step in previous works was the blueprint of an LOQC architecture that could be conceivably implemented with idealised optical components. However, in reality nature is not kind and devices not ideal. As such, we consider open questions addressing gaps between LOQC's theoretical architecture and experimental constraints. In doing so, a selection of numerical tools are also developed for the design, simulation and analyses of novel architectures. Specifically, we consider three problems. Firstly, can an infinite-sized quantum state be realised within a finite-sized device? Through development of a simple, generalised model, we find some small, finite device size at which the infinite state is faithfully reproduced. We also find that increasing device size above this confers no advantage, thereby identifying some necessary and sufficient minimum LOQC device size. Secondly, we consider the challenge of accommodating unheralded photon loss in an LOQC architecture, a problem for which no previous solution was known. By developing a novel protocol for optimal teleportation on stabilizer states, we show that unheralded loss may be tolerated, perhaps entirely, by adaptive measurement strategies. Finally, we consider the optimisation of LOQC architectures via local complementation. This work both sets hard limits on the states accessible by postselected linear optics circuits as well as develops novel tools for the analysis of higher-dimensional quantum states. We conclude with an example of how such works can be combined to optimise the LOQC architecture as w

关键词： quantum computing linear optical quantum computing photonics quantum computing architectures

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quantum Computation via Multiport Discretized quantum Fourier optical Processors

IEEE TRANSACTIONS ON QUANTUM ENGINEERING

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IEEE TRANSACTIONS ON quantum ENGINEERING 2024年第1期5卷 1页

作者： Rezai, Mohammad Salehi, Jawad A. Sharif Univ Technol Inst Convergence Sci & Technol Ctr Quantum Sci & Technol Tehran *** Iran Sharif Univ Technol Sharif Quantum Ctr Tehran *** Iran Sharif Univ Technol Dept Elect Engn Tehran 111554363 Iran

The light's image is the primary source of information carrier in nature. Indeed, a single photon's image possesses a vast information capacity that can be harnessed for quantum information processing. Our scheme for implementing quantum information processing on a discretized photon wavefront via universal multiport processors employs a class of quantum Fourier optical systems composed of spatial phase modulators and 4f-processors with phase-only pupils having a characteristic periodicity that reduces the number of optical resources quadratically as compared to other conventional path-encoding techniques. In particular, this article employs quantum Fourier optics to implement some key quantum logical gates that can be instrumental in optical quantum computations. For instance, we demonstrate the principle by implementing the single-qubit Hadamard and the two-qubit controlled-not gates via simulation and optimization techniques. Due to various advantages of the proposed scheme, including the large information capacity of the photon wavefront, a quadratically reduced number of optical resources compared with other conventional path-encoding techniques, and dynamic programmability, the proposed scheme has the potential to be an essential contribution to linear optical quantum computing and optical quantum signal processing.

关键词： Photonics optical interferometry quantum computing Integrated optics Adaptive optics optical imaging optical signal processing CNOT gate discrete unitary operator Fourier optical quantum computing Hadamard gate linear optical quantum computing quantum Fourier optics universal multiport interferometer universal multiport processor

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A Software Platform for Programmable linear optical quantum Computer

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IEEE ACCESS 2023年 11卷 112682-112692页

作者： Kwon, Yong Choi, Byung-Soo Pukyong Natl Univ Dept Phys Busan 48513 South Korea Pukyong Natl Univ Dept Sci Comp Busan 48513 South Korea

optical quantum computers represent qubits as photons created by laser and implement arbitrary quantum operations through Mach-Zehnder interferometers (MZIs) which is called linear optical quantum computing (LOQC). Since the number of qubits and quantum system is getting bigger, we need a scalable and universal quantum computing platform based on LOQC. In this work, we propose a software framework which can support a universal programming with flexibility of LOQC hardware configuration. The framework consists of four parts such as decomposer, mapper, controller, and user-interface controller. As an example, we show a use case of this framework for Bell state generation on Reck et al.'s MZI network.

关键词： quantum computer software linear optical quantum computing

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Simple rules for two-photon state preparation with linear optics 5

Simple rules for two-photon state preparation with linear op...

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2024 International Conference on quantum computing and Engineering

作者： de Gliniasty, Gregoire Bagourd, Paul Draux, Sebastien Bourdoncle, Boris Quandela Massy France LIP6 Paris France Ecole Polytech Fed Lausanne Lausanne Switzerland

ISBN: (纸本)9798331541378

Entangling photons is a critical challenge for photonic quantum information processing: entanglement is a crucial resource for quantum communication and computation but can only be performed in a probabilistic manner when using linear optics. In this work, we leverage a two-photon state matrix representation to derive necessary and sufficient conditions on two-photon entangling operations with linear optics. We give a characterization of the input photonic states that can be used to prepare arbitrary two-qudit states in d-rail encoding with post-selection. We determine how many auxiliary photons are required to prepare any two-photon state with heralding. In addition, we present a construction for generalized post-selected n-qubit control-rotation gates Cn-1 Z(phi).

关键词： Entangled state preparation linear optical quantum computing Photonic entanglement Qudit quantum computing

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The influence of experimental imperfections on photonic GHZ state generation

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NEW JOURNAL OF PHYSICS 2024年第11期26卷 113021页

作者： Wiesner, Fabian Chrzanowski, Helen M. Pieplow, Gregor Schroeder, Tim Pappa, Anna Wolters, Janik Tech Univ Berlin Elect Engn & Comp Sci Dept D-10587 Berlin Germany Deutsch Zent Luft & Raumfahrt eV DLR Inst Opt Sensor Syst D-12489 Berlin Germany Humboldt Univ Dept Phys D-12489 Berlin Germany Ferdinand Braun Inst D-12489 Berlin Germany Fraunhofer Inst Open Commun Syst FOKUS D-10589 Berlin Germany Tech Univ Berlin Inst Opt & Atom Phys D-10623 Berlin Germany

While the advantages of photonic quantum computing, including direct compatibility with communication, are apparent, several imperfections such as loss and distinguishability presently limit actual implementations. These imperfections are unlikely to be completely eliminated, and it is therefore beneficial to investigate which of these are the most dominant and what is achievable under their presence. In this work, we provide an in-depth investigation of the influence of photon loss, multi-photon terms and photon distinguishability on the generation of photonic 3-partite Greenberger-Horne-Zeilinger states via established fusion protocols. We simulate the generation process for spontaneous parametric down-conversion and solid-state-based single-photon sources using realistic parameters and show that different types of imperfections are dominant with respect to the fidelity and generation success probability. Our results indicate what are the dominant imperfections for the different photon sources and in which parameter regimes we can hope to implement photonic quantum computing in the near future.

关键词： linear optical quantum computing quantum simulation experimental imperfections photonic GHZ state

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Active learning on a programmable photonic quantum processor

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quantum SCIENCE AND TECHNOLOGY 2023年第3期8卷 035030-035030页

作者： Ding, Chen Xu, Xiao-Yue Niu, Yun-Fei Zhang, Shuo Huang, He-Liang Bao, Wan-Su Henan Key Lab Quantum Informat & Cryptog Zhengzhou 450000 Henan Peoples R China Univ Sci & Technol China Hefei Natl Lab Hefei 230088 Peoples R China

Training a quantum machine learning model generally requires a large labeled dataset, which incurs high labeling and computational costs. To reduce such costs, a selective training strategy, called active learning (AL), chooses only a subset of the original dataset to learn while maintaining the trained model's performance. Here, we design and implement two AL-enpowered variational quantum classifiers to investigate the potential applications and effectiveness of AL in quantum machine learning. Firstly, we build a programmable free-space photonic quantum processor, which enables the programmed implementation of various hybrid quantum-classical computing algorithms. Then, we code the designed variational quantum classifier with AL into the quantum processor, and execute comparative tests for the classifiers with and without the AL strategy. The results validate the great advantage of AL in quantum machine learning, as it saves at most 85% labeling efforts and 91.6% percent computational efforts compared to the training without AL on a data classification task. Our results inspire AL's further applications in large-scale quantum machine learning to drastically reduce training data and speed up training, underpinning the exploration of practical quantum advantages in quantum physics or real-world applications.

关键词： quantum machine learning linear optical quantum computing active learning

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Integrated programmable controlled phase gate design for quantum information processing

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PHYSICA SCRIPTA 2023年第10期98卷 105109-105109页

作者： Basay, Yalin Kocaman, Serdar Middle East Tech Univ Micro & Nanotechnol Ankara Turkiye Middle East Tech Univ Elect Elect Engn Ankara Turkiye

An integrated programmable controlled-phase (CPHASE) gate has been proposed for quantum information processing applications. This gate can introduce arbitrary phase difference to the target qubit in the case of the control qubit being in the state of |1. As the desired phase difference can be utilized after fabrication, unlike the conventional controlled-phase gates that provide hard-coded phase shift, such an integrated gate is expected to pave the way for more versatile operations of current integrated optical circuits as well as possible new applications.

关键词： linear optical quantum computing integrated optics CPHASE gate polarization rotator

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Modeling two-qubit Grover's algorithm implementation in a linear optical chip

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PHYSICA SCRIPTA 2020年第4期95卷 045102-045102页

作者： Samsonov, E. Kiselev, F. Shmelev, Y. Egorov, V Goncharov, R. Santev, A. Pervushin, B. Gleim, A. ITMO Univ Kronverkskiy 49 St Petersburg 197101 Russia Corning Res & Dev Corp Corning NY USA

This paper introduces a model of Grover's algorithm suitable for implementation in a linear photonic chip. We compare two known realizations of its main components, two-qubit CZ gates, in order to define optimal chip architecture. The algorithm operation is simulated considering directional coupler imperfection influence on the scheme parameters. We also determined tolerance boundaries for distortions of the coupler dimensions.

关键词： quantum computing Grovers algorithm optical chip linear optical quantum computing

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Hard limits on the postselectability of optical graph states

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quantum SCIENCE AND TECHNOLOGY 2019年第1期4卷

作者： Adcock, Jeremy C. Morley-Short, Sam Silverstone, Joshua W. Thompson, Mark G. Univ Bristol QETLabs HH Wills Phys Lab Merchant Venturers BldgWoodland Rd Bristol BS8 1UB Avon England Univ Bristol Dept Elect & Elect Engn Merchant Venturers BldgWoodland Rd Bristol BS8 1UB Avon England

Coherent control of large entangled graph states enables a wide variety of quantum information processing tasks, including error-corrected quantum computation. The linear optical approach offers excellent control and coherence, but today most photon sources and entangling gates-required for the construction of large graph states-are probabilistic and rely on postselection. In this work, we provide proofs and heuristics to aid experimental design using postselection. We introduce a versatile design rule for postselectable experiments: drawn as a graph, with qubit as vertices and gates and photon-pair sources as edges, an experiment may only contain cycles with an odd number of sources. We analyse experiments that use photons from postselected photon-pair sources, and lower bound the number of accessible classes of graph state entanglement in the non-degenerate case-graph state entanglement classes that contain a tree are are always accessible. The proportion of graph states accessible by postselection shrinks rapidly, however. We list accessible classes for various resource states up to 9 qubits. Finally, we apply these methods to near-term multi-photon experiments.

关键词： entanglement graph states postselection photon sources photonic experiment design linear optical quantum computing numerical methods

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Physical-depth architectural requirements for generating universal photonic cluster states

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quantum SCIENCE AND TECHNOLOGY 2018年第1期3卷

作者： Morley-Short, Sam Bartolucci, Sara Gimeno-Segovia, Mercedes Shadbolt, Pete Cable, Hugo Rudolph, Terry Univ Bristol HH Wills Phys Lab Quantum Engn Technol Labs Bristol BS8 1FD Avon England Univ Bristol Dept Elect & Elect Engn Bristol BS8 1FD Avon England Univ Bristol Quantum Engn Ctr Doctoral Training HH Wills Phys Lab Tyndall Ave Bristol BS8 1FD Avon England Univ Bristol Dept Elect & Elect Engn Tyndall Ave Bristol BS8 1FD Avon England Imperial Coll London Dept Phys London SW7 2AZ England Univ Calgary Inst Quantum Sci & Technol Calgary AB T2N 1N4 Canada

Most leading proposals for linear-optical quantum computing (LOQC) use cluster states, which act as a universal resource for measurement-based (one-way) quantum computation. In ballistic approaches to LOQC, cluster states are generated passively from small entangled resource states using so-called fusion operations. Results from percolation theory have previously been used to argue that universal cluster states can be generated in the ballistic approach using schemes which exceed the critical threshold for percolation, but these results consider cluster states with unbounded size. Here we consider how successful percolation can be maintained using a physical architecture with fixed physical depth, assuming that the cluster state is continuously generated and measured, and therefore that only a finite portion of it is visible at any one point in time. We show that universal LOQC can be implemented using a constant-size device with modest physical depth, and that percolation can be exploited using simple pathfinding strategies without the need for high-complexity algorithms.

关键词： quantum computing linear optical quantum computing applied percolation theory quantum computer architectures

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