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quantum simulation of a discrete-time quantum stochastic walk

EPL 2021年第5期133卷 50003-50003页

作者： Schuhmacher, Peter K. Govia, Luke C. G. Taketani, Bruno G. Wilhelm, Frank K. Saarland Univ Theoret Phys D-66123 Saarbrucken Germany Forschungszentrum Julich Inst Quantum Comp Analyt PGI12 D-52425 Julich Germany Raytheon BBN Technol 10 Moulton St Cambridge MA 02138 USA Univ Fed Santa Catarina Dept Fis BR-88040900 Florianopolis SC Brazil

quantum walks have been shown to have a wide range of applications, from artificial intelligence, to photosynthesis, and quantum transport. quantum stochastic walks (QSWs) generalize this concept to additional non-unitary evolution. In this paper, we propose a trajectory-based quantum simulation protocol to effectively implement a family of discrete-time QSWs in a quantum device. After deriving the protocol for a 2-vertex graph with a single edge, we show how our protocol generalizes to a graph with arbitrary topology and connectivity. The straightforward generalization leads to simple scaling of the protocol to complex graphs. Finally, we show how to simulate a restricted class of continuous-time QSWs by a discrete-time QSW, and how this is amenable to our simulation protocol for discrete-time QSWs. Copyright (C) 2021 EPLA

关键词： quantum computation architectures and implementations Stochastic processes

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quantum state transfer between nitrogen vacancy center ensembles in hybrid quantum system

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EPL 2019年第3期127卷 30007-30007页

作者： Ali, Hamad Basit, Abdul Badshah, Fazal Qurban, Misbah Ge, Guo-Qin Huazhong Univ Sci & Technol Sch Phys Wuhan 430074 Hubei Peoples R China COMSATS Univ Islamabad Quantum Opt Lab Dept Phys Islamabad Pakistan Fatima Jinnah Women Univ Mall Dept Phys Rawalpindi Pakistan

We propose a system for quantum state transfer (QST) between two nitrogen-vacancy center ensembles (NVEs) coupled to two transmission line resonators (TLRs) via flux qubits (FQs). We study the transfer of an arbitrary quantum state by various system's controlling parameters i.e., the coupling between nitrogen vacancy ensembles g, the coupling strength between resonators. for both the resonant and non-resonant interactions in the presence of decoherence. Furthermore, we investigate the dynamics of QST for three different cases, i.e., g >> lambda, g similar or equal to and g << lambda in detail. It is found that the quantum state can be efficiently transferred between NVEs for suitable values of controlling parameters. We observe that the fidelity of quantum state transfer is about 99% in all cases for short operational time (0.45 mu s) while in the presence of decoherence fidelity is above 96%. This reveals that decoherence has no prominent effect on quantum state transfer. Copyright (C) EPLA, 2019.

关键词： quantum information Vacancies quantum computation architectures and implementations

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Implementation of a fixed-point quantum search by duality computer

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EPL 2019年第2期126卷 20004-20004页

作者： Ding, Lei Zhou, Tao Southwest Jiaotong Univ Sch Phys Sci & Technol Chengdu 611756 Sichuan Peoples R China

The quantum algorithms where the operations are unitary can be implemented by an ordinary quantum computer, and nonunitary operations can be realized in the duality computer. The operations in the fixed-point quantum search proposed by Mizel (Phys. Rev. Lett., 102 (2009) 150501) are not unitary, and in this paper it is shown that this algorithm can effectively be implemented in duality quantum computer. Copyright (C) EPLA, 2019

关键词： quantum computation architectures and implementations quantum algorithms, protocols, and simulations

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Mathematical formulation of quantum circuit design problems in networks of quantum computers

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quantum INFORMATION PROCESSING 2020年第5期19卷 141-141页

作者： van Houte, R. Mulderij, J. Attema, T. Chiscop, I. Phillipson, F. TNO The Hague Netherlands Delft Univ Technol Delft Netherlands CWI Amsterdam Netherlands Leiden Univ Leiden Netherlands

In quantum circuit design, the question arises how to distribute qubits, used in algorithms, over the various quantum computers, and how to order them within a quantum computer. In order to evaluate these problems, we define the global and local reordering problems for distributed quantum computing. We formalise the mathematical problems and model them as integer linear programming problems, to minimise the number of SWAP gates or the number of interactions between different quantum computers. For global reordering, we analyse the problem for various geometries of networks: completely connected networks, general networks, linear arrays and grid-structured networks. For local reordering, in networks of quantum computers, we also define the mathematical optimisation problem.

关键词： Nearest neighbour compliant quantum computation architectures and implementations Distributed quantum computing

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New trends in quantum machine learning

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EPL 2020年第6期132卷

作者： Buffoni, Lorenzo Caruso, Filippo Univ Firenze Dipartimento Fis & Astron I-50019 Sesto Fiorentino Italy Univ Firenze Dipartimento Ingn Informaz I-50199 Florence Italy QSTAR LENS I-50019 Sesto Fiorentino Italy CNR INO I-50019 Sesto Fiorentino Italy

Here we will give a perspective on new possible interplays between machine learning and quantum physics, including also practical cases and applications. We will explore the ways in which machine learning could benefit from new quantum technologies and algorithms to find new ways to speed up their computations by breakthroughs in physical hardware, as well as to improve existing models or devise new learning schemes in the quantum domain. Moreover, there are lots of experiments in quantum physics that do generate incredible amounts of data and machine learning would be a great tool to analyze those and make predictions, or even control the experiment itself. On top of that, data visualization techniques and other schemes borrowed from machine learning can be of great use to theoreticians to have better intuition on the structure of complex manifolds or to make predictions on theoretical models. This new research field, named as quantum machine learning, is very rapidly growing since it is expected to provide huge advantages over its classical counterpart and deeper investigations are timely needed since they can be already tested on the already commercially available quantum machines. Copyright (C) 2021 EPLA

关键词： quantum algorithms, protocols, and simulations quantum computation architectures and implementations

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Unitary quantum perceptron as efficient universal approximator

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EPL 2019年第3期125卷 30004-30004页

作者： Torrontegu, E. Garcia-Ripoll, J. J. CSIC IFF Calle Serrano 113b Madrid 28006 Spain

We demonstrate that it is possible to implement a quantum perceptron with a sigmoid activation function as an efficient, reversible many-body unitary operation. When inserted in a neural network, the perceptron's response is parameterized by the potential exerted by other neurons. We prove that such a quantum neural network is a universal approximator of continuous functions, with at least the same power as classical neural networks. While engineering general perceptrons is a challenging control problem -also defined in this work- the ubiquitous sigmoid-response neuron can be implemented as a quasi-adiabatic passage with an Ising model. In this construct, the scaling of resources is favorable with respect to the total network size and is dominated by the number of layers. We expect that our sigmoid perceptron will have applications also in quantum sensing or variational estimation of many-body Hamiltonians. Copyright (C) EPLA 2019

关键词： quantum information quantum computation architectures and implementations

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Deep reinforcement learning for quantum gate control

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EPL 2019年第6期126卷 60002-60002页

作者： An, Zheng Zhou, D. L. Chinese Acad Sci Inst Phys Beijing Natl Lab Condensed Matter Phys Beijing 100190 Peoples R China Univ Chinese Acad Sci Sch Phys Sci Beijing 100049 Peoples R China Collaborat Innovat Ctr Quantum Matter Beijing 100190 Peoples R China Songshan Lake Mat Lab Dongguan 523808 Guangdong Peoples R China

How to implement multi-qubit gates efficiently with high precision is essential for realizing universal fault-tolerant computing. For a physical system with some external controllable parameters, it is a great challenge to control the time dependence of these parameters to achieve a target multi-qubit gate efficiently and precisely. Here we construct a dueling double deep Q-learning neural network (DDDQN) to find out the optimized time dependence of controllable parameters to implement two typical quantum gates: a single-qubit Hadamard gate and a two-qubit CNOT gate. Compared with traditional optimal control methods, this deep reinforcement learning method can realize efficient and precise gate control without requiring any gradient information during the learning process. This work attempts to pave the way to investigate more quantum control problems with deep reinforcement learning techniques. Copyright (C) EPLA, 2019.

关键词： quantum algorithms, protocols, and simulations quantum computation architectures and implementations Neural networks, fuzzy logic, artificial intelligence

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Constructing multi-target controlled phase gate in circuit QED and its applications

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EPL 2019年第5期127卷 50002-50002页

作者： Han, Jin-Xuan Wu, Jin-Lei Wang, Yan Xia, Yan Song, Jie Jiang, Yong-Yuan Harbin Inst Technol Dept Phys Harbin 150001 Heilongjiang Peoples R China Fuzhou Univ Dept Phys Fuzhou 350002 Fujian Peoples R China

We present a one-step scheme in circuit quantum electrodynamics (QED) to realize multi-target controlled phase gates by using one microwave cavity that is coupled capacitively to a superconducting flux qutrit which plays the control role and simultaneously controls n target qutrits embedded in the microwave cavity. A strong classical field is imposed on the control qutrit so as to yield two dressed states, one of which is coded as a logical state. The controlled phase gates can be employed to achieve the creation of entangled states deterministically without any measurement, including the Bell state, the GHZ state, and the cluster state. Numerical simulations demonstrate that the high-fidelity creation of the entangled state is feasible with the constructed controlled phase gate under the present circuit QED technology. Copyright (C) EPLA, 2019

关键词： quantum computation architectures and implementations Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.) Entanglement measures, witnesses, and other characterizations

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quantum state-to-state dynamics of O⁺+ H2(ν=0, j=0) → OH⁺ (ν′, j′) plus H reaction on a global potential energy surface

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EPL 2019年第5期126卷 53001-53001页

作者： Xu, Ting Zhang, Jinyu Zhao, Juan Song, Yuzhi Meng, Qingtian Shandong Normal Univ Sch Phys & Elect Jinan 250358 Shandong Peoples R China Shandong Jiaotong Univ Coll Sci Jinan 250357 Shandong Peoples R China

The state-to-state quantum dynamics calculation for the reaction O++ H-2 -> OH+ + H is implemented based on a global potential energy surface. The reaction probabilities, state-resolved integral and differential cross sections are obtained and discussed. Due to the existence of the potential well, the reaction probabilities exhibit obvious oscillating features. And as a typical system of heavy-light-light mass combination, this reaction is more conducive to the occurrence of the product rotational excitation. So when the products are mainly concentrated in nu' = 0 and nu' = 1 states, the distribution of the product rotational, rather than vibrational, state-resolved integral cross section shows an inversion phenomenon. Furthermore, became of the quantum interference of the rovibrational wave functions, the rotational resolution integral cross section of the product displays a multipeak structure, and this phenomenon becomes less obvious as the collision energy increases. Meanwhile, the total differential cross sections are found to be peaked both forwardly and backwardly, which indicates that there exists a complex-forming mechanism in the reaction. With the increase of collision energy, the feature of differential cross section is from the forward-backward scattering to the forward scattering. Copyright (C) EFLA, 2019

关键词： Molecular dynamics and other numerical methods Scattering of atoms and molecules quantum computation architectures and implementations

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Auxiliary-qubit-driving-induced entanglement and logic gate

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EPL 2019年第3期126卷 30001-30001页

作者： Wu, Jin-Lei Su, Shi-Lei Zhengzhou Univ Sch Phys & Engn Zhengzhou 450001 Henan Peoples R China Harbin Inst Technol Dept Phys Harbin 150001 Heilongjiang Peoples R China

A one-step scheme to remotely create a two-atom Einstein-Podolsky-Rosen (EPR) entangled state and a quantum logic gate via exchanging the virtual photon is proposed. Two systematic atoms require no laser driving but get entangled, while the state of the auxiliary atom requiring laser driving always remains invariant. The scheme may have applications in the remote quantum information processing (QIP) tasks and quantum computation. The robustness against decoherence is demonstrated numerically and discussed in theory. In addition, the experimental issues and improvement of the scheme are also discussed. Copyright (C) EPLA, 2019

关键词： Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.) quantum computation architectures and implementations Entanglement measures, witnesses, and other characterizations

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