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A Secure Multiparty quantum Homomorphic Encryption Scheme

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Computers, Materials & Continua 2022年第11期73卷 2835-2848页

作者： Jing-Wen Zhang Xiu-Bo Chen Gang Xu Heng-Ji Li Ya-Lan Wang Li-Hua Miao Yi-Xian Yang Information Security Center State Key Laboratory of Networking and Switching TechnologyBeijing University of Posts and TelecommunicationsBeijing100876China School of Information Science and Technology North China University of TechnologyBeijing100144China Advanced Cryptography and System Security Key Laboratory of Sichuan Province Sichuan610025China Quantum Technology Lab&Applied Mechanics Group University of MilanMilan20133Italy Department of Computer Science Faculty of Engineering and Physical SciencesUniversity of SurreyGuildfordSurreyGU27XHUnited Kingdom Huawei Technologies Co.Ltd Shenzhen518129China

The significant advantage of the quantum homomorphic encryption scheme is to ensure the perfect security of quantum private *** this paper,a novel secure multiparty quantum homomorphic encryption scheme is proposed,which can complete arbitrary quantum computation on the private data of multiple clients without decryption by an almost dishonest ***,each client obtains a secure encryption key through the measurement device independent quantum key distribution protocol and encrypts the private data by using the encryption operator and ***,with the help of the almost dishonest server,the non-maximally entangled states are preshared between the client and the server to correct errors in the homomorphic evaluation of T gates,so as to realize universal quantum circuit evaluation on encrypted ***,from the perspective of the application scenario of secure multi-party computation,this work is based on the probabilistic quantum homomorphic encryption scheme,allowing multiple parties to delegate the server to perform the secure homomorphic *** operation and the permission to access the data performed by the client and the server are clearly pointed ***,a concrete security analysis shows that the proposed multiparty quantum homomorphic encryption scheme can securely resist outside and inside attacks.

关键词： quantum homomorphic encryption secure multiparty computation almost dishonest server security

quantum-classical distance as a tool to design optimal chiral quantum walks

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Physical Review A 2022年第3期105卷 032425-032425页

作者： Massimo Frigerio Claudia Benedetti Stefano Olivares Matteo G. A. Paris Quantum Technology Lab and Applied Quantum Mechanics Group Dipartimento di Fisica Aldo Pontremoli Università Degli Studi di Milano Milano I-20133 Italy INFN Sezione di Milano Milano I-20133 Italy

Continuous-time quantum walks (CTQWs) provide a valuable model for quantum transport, universal quantum computation, and quantum spatial search, among others. Recently, the empowering role of new degrees of freedom in the Hamiltonian generator of CTQWs, which are the complex phases along the loops of the underlying graph, was acknowledged for its interest in optimizing or suppressing transport on specific topologies. We argue that the quantum-classical distance, a figure of merit which was introduced to capture the difference in dynamics between a CTQW and its classical, stochastic counterpart, guides the optimization of parameters of the Hamiltonian to achieve better quantum transport on cycle graphs and spatial search for the quantum speed limit without an oracle on complete graphs, the latter also implying fast uniform mixing. We compare the variations of this quantity with the 1-norm of coherence and the inverse participation ratio, showing that the quantum-classical distance is linked to both, but in a topology-dependent relation, which is key to spot the most interesting quantum evolution in each case.

关键词： quantum algorithms quantum walks

Generalized quantum-classical correspondence for random walks on graphs

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Physical Review A 2021年第3期104卷 L030201-L030201页

We introduce a minimal set of physically motivated postulates that the Hamiltonian H of a continuous-time quantum walk should satisfy in order to properly represent the quantum counterpart of the classical random walk on a given graph. We found that these conditions are satisfied by infinitely many quantum Hamiltonians, which provide novel degrees of freedom for quantum enhanced protocols, In particular, the on-site energies, i.e., the diagonal elements of H, and the phases of the off-diagonal elements are unconstrained on the quantum side. The diagonal elements represent a potential-energy landscape for the quantum walk and may be controlled by the interaction with a classical scalar field, whereas, for regular lattices in generic dimension, the off-diagonal phases of H may be tuned by the interaction with a classical gauge field residing on the edges, e.g., the electromagnetic vector potential for a charged walker.

关键词： Continuous-time random walk quantum walks Random walks Gauge symmetries Graph theory

Mechanical oscillator thermometry in the nonlinear optomechanical regime

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Physical Review Research 2020年第4期2卷 043338-043338页

作者： V. Montenegro M. G. Genoni A. Bayat M. G. A. Paris Institute of Fundamental and Frontier Sciences University of Electronic Science and Technology of China Chengdu 610051 China Quantum Technology Lab & Applied Quantum Mechanics Group Dipartimento di Fisica Aldo Pontremoli Università degli Studi di Milano I-20133 Milano Italy

Optomechanical systems are promising platforms for controlled light-matter interactions. They are capable of providing several fundamental and practical novel features when the mechanical oscillator is cooled down to nearly reach its ground state. In this framework, measuring the effective temperature of the oscillator is perhaps the most relevant step in the characterization of those systems. In conventional schemes, the cavity is driven strongly, and the overall system is well-described by a linear (Gaussian preserving) Hamiltonian. Here, we depart from this regime by considering an undriven optomechanical system via non-Gaussian radiation-pressure interaction. To measure the temperature of the mechanical oscillator, initially in a thermal state, we use light as a probe to coherently interact with it and create an entangled state. We show that the optical probe gets a nonlinear phase, resulting from the non-Gaussian interaction, and undergoes an incoherent phase diffusion process. To efficiently infer the temperature from the entangled light-matter state, we propose using a nonlinear Kerr medium before a homodyne detector. Remarkably, placing the Kerr medium enhances the precision to nearly saturate the ultimate quantum bound given by the quantum Fisher information. Furthermore, it also simplifies the thermometry procedure as it makes the choice of the homodyne local phase independent of the temperature.

关键词： Optomechanics quantum metrology quantum parameter estimation quantum sensing

Probing of nonlinear hybrid optomechanical systems via partial accessibility

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Physical Review Research 2022年第3期4卷 033036-033036页

Hybrid optomechanical systems are emerging as a fruitful architecture for quantum technologies. Hence determining the relevant atom-light and light-mechanics couplings is an essential task in such systems. The fingerprint of these couplings is left in the global state of the system during nonequilibrium dynamics. However, in practice, performing measurements on the entire system is not feasible, and thus one has to rely on partial access to one of the subsystems, namely, the atom, the light, or the mechanics. Here we perform a comprehensive analysis to determine the optimal subsystem for probing the couplings. We find that if the light-mechanics coupling is known or irrelevant, depending on the range of the qubit-light coupling, then the optimal subsystem can be either the light or the qubit. In other scenarios, e.g., simultaneous estimation of the couplings, the light is usually the optimal subsystem. This can be explained as light is the mediator between the other two subsystems. Finally, we show that the widely used homodyne detection can extract a fair fraction of the information about the couplings from the light degrees of freedom.

关键词： Cavity quantum electrodynamics Hybrid quantum systems Optomechanics quantum metrology quantum parameter estimation

Cost-effective temperature estimation strategies for thermal states with probabilistic quantum metrology

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arXiv 2021年

作者： Frigerio, Massimo Olivares, Stefano Paris, Matteo G.A. Quantum Technology Lab & Applied Quantum Mechanics Group Dipartimento di Fisica "Aldo Pontremoli" Università degli Studi di Milano MilanoI-20133 Italy INFN Sezione di Milano MilanoI-20133 Italy

In probabilistic quantum metrology, one aims at finding weak measurements that concentrate the Fisher Information on the resulting quantum states, post-selected according to the weak outcomes. Though the quantum Cramér-Rao bound itself cannot be overshot this way, it could be possible to improve the information-cost ratio, or even the total Fisher Information. We propose a post-selection protocol achieving this goal based on single-photon subtraction onto a thermal state of radiation yielding a greater information-cost ratio for the temperature parameter with respect to the standard strategy required to achieve the quantum Cramér-Rao bound. We address just fully-classical states of radiation: this contrasts with (but does not contradict) a recent result proving that, concerning unitary quantum estimation problems, post-selection strategies can outperform direct measurement protocols only if a particular quasiprobability associated with the family of parameter-dependent quantum states becomes negative, a clear signature of nonclassicality. © 2021, CC BY.

关键词： Fisher information matrix

quantum-classical distance as a tool to design optimal chiral quantum walks

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arXiv 2021年

作者： Frigerio, Massimo Benedetti, Claudia Olivares, Stefano Paris, Matteo G.A. Quantum Technology Lab and Applied Quantum Mechanics Group Dipartimento di Fisica Aldo Pontremoli Università Degli Studi di Milano MilanoI-20133 Italy INFN Sezione di Milano MilanoI-20133 Italy

Continuous-time quantum walks (CTQWs) provide a valuable model for quantum transport, universal quantum computation and quantum spatial search, among others. Recently, the empowering role of new degrees of freedom in the Hamiltonian generator of CTQWs, which are the complex phases along the loops of the underlying graph, was acknowledged for its interest in optimizing or suppressing transport on specific topologies. We argue that the quantum-classical distance, a figure of merit which was introduced to capture the difference in dynamics between a CTQW and its classical, stochastic counterpart, guides the optimization of parameters of the Hamiltonian to achieve better quantum transport on cycle graphs and spatial search to the quantum speed limit without an oracle on complete graphs, the latter also implying fast uniform mixing. We compare the variations of this quantity with the 1-norm of coherence and the Inverse Participation Ratio, showing that the quantum-classical distance is linked to both, but in a topology-dependent relation, which is key to spot the most interesting quantum evolution in each case. © 2021, CC BY.

关键词： Hamiltonians

Generalized quantum-classical correspondence for random walks on graphs

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arXiv 2021年

作者： Frigerio, Massimo Benedetti, Claudia Olivares, Stefano Paris, Matteo G.A. Quantum Technology Lab Applied Quantum Mechanics Group Dipartimento di Fisica Aldo Pontremoli Università Degli Studi di Milano MilanoI-20133 Italy Infn Sezione di Milano MilanoI-20133 Italy

We introduce a minimal set of physically motivated postulates that the Hamiltonian H of a continuous-time quantum walk should satisfy in order to properly represent the quantum counterpart of the classical random walk on a given graph. We found that these conditions are satisfied by infinitely many quantum Hamiltonians, which provide novel degrees of freedom for quantum enhanced protocols, In particular, the on-site energies, i.e. the diagonal elements of H, and the phases of the off-diagonal elements are unconstrained on the quantum side. The diagonal elements represent a potential energy landscape for the quantum walk, and may be controlled by the interaction with a classical scalar field, whereas, for regular lattices in generic dimension, the off-diagonal phases of H may be tuned by the interaction with a classical gauge field residing on the edges, e.g., the electro-magnetic vector potential for a charged walker. © 2021, CC BY.

关键词： Degrees of freedom (mechanics)

quantum Metrology with Boundary Time Crystals

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arXiv 2023年

作者： Montenegro, Victor Genoni, Marco G. Bayat, Abolfazl Paris, Matteo G.A. Institute of Fundamental and Frontier Sciences University of Electronic Science and Technology of China Chengdu610051 China Quantum Technology Lab & Applied Quantum Mechanics Group Dipartimento di Fisica "Aldo Pontremoli" Università degli Studi di Milano MilanoI-20133 Italy

quantum sensing is one of the arenas that exemplifies the superiority of quantum technologies over their classical counterparts. Such superiority, however, can be diminished due to unavoidable noise and decoherence of the probe. Thus, metrological strategies to fight against or profit from decoherence are highly desirable. This is the case of certain types of decoherence-driven many-body systems supporting dissipative phase transitions, which might be helpful for sensing. Boundary time crystals are exotic dissipative phases of matter in which the time-translational symmetry is broken, and long-lasting oscillations emerge in open quantum systems at the thermodynamic limit. We show that the transition from a symmetry unbroken into a boundary time crystal phase, described by a second-order transition, reveals quantum-enhanced sensitivity quantified through quantum Fisher information. We also determine the critical exponents of the system and establish their relationship. Our scheme is indeed a demonstration of harnessing decoherence for achieving quantum-enhanced sensitivity. From a practical perspective, it has the advantage of being independent of initialization and can be captured by a simple measurement. Copyright © 2023, The Authors. All rights reserved.

关键词： Phase transitions