Quantum Information Processing最新文献

Quantum entanglement is one of the most crucial resources in quantum information. Its robustness, in a certain sense, quantifies the tolerance of entanglement against noise and interference. By studying the robustness of entanglement for mixed states composed of entangled pure states, it’s helpful to understand the robustness of entanglement in more general states. In this work, we present an analytical method for evaluating the robustness of entanglement for W and GHZ mixed states involving three and four qubits. By employing the definition of the robustness of entanglement and analyzing the entanglement witness, we establish tight upper and lower bounds for the robustness of these mixed states. The calculated results demonstrate the accuracy of our approach, offering insights for studying the robustness of entanglement for general quantum states.

Without a doubt, temperature control and measurement are crucial for every prospective application in various quantum-operating systems and platforms. The theory of quantum thermometry will have a significant influence on and shape the upcoming quantum technologies, together with the advancement of measurement procedures and new experimental techniques. At the intersection of quantum metrology, open quantum systems and quantum many-body physics, the theory of quantum thermometry is constructed under a unifying framework, despite the fact that current quantum thermometric methods vary greatly depending on the experimental platform, the achievable precision and the temperature range of interest. Finding the absolute limits and scaling rules that restrict the accuracy of temperature estimation for systems in and out of thermal equilibrium is at the core of theoretical quantum thermometry. Although quantum Fisher information is monotonically decreasing under the action of a quantum channel or noises, we address that the information losses under any quantum operation by offering relative improvements to minimize uncertainty for estimating of temperature for different output states obtained by Hamiltonians constructed with the quantum Yang–Baxter equation can be mitigated.

States whose entanglement can be detected by a fidelity-based entanglement witness are faithful. In this paper, we introduce a new necessary and sufficient condition for identifying faithful states. This condition is based on the trace norm. With the help of this condition, we investigate the effect of local channels on the faithfulness of two-qubit entangled states. The result shows that all the unital channels cannot enhance the faithfulness of entangled states. Some non-unital channels can improve the faithfulness of a restricted set of entangled states and even change an unfaithful entangled state to a faithful one. However, the faithfulness of all the states with maximally mixed marginals can only decrease when subjected to local channels.

In distributed systems, Byzantine consensus serves as a practical approach to addressing the Byzantine general problem. Previous research has exploited quantum resources to develop quantum detectable Byzantine consensus protocols, aiming to surpass the 1/3 fault tolerance bound. However, these consensus protocols are designed under the assumption of secure channel. They ignored malicious participants’ attacks on the communication process. In this paper, we introduce a new quantum protocol for quantum Byzantine consensus utilizing the full quantum one-way function, which is the foundation for generating verification state in list distribution phase and secure message in agreement phase. By relying on the quantum circuit of the full quantum one-way function, the honest participants are able to reach consensus, while the malicious participants are effectively detected. In order to enhance the scalability of the proposed quantum Byzantine consensus protocol, we categorize the participants into three-member groups when the number of participants is (n>3). Meanwhile, the election of commander is introduced in agreement phase. In the proposed multi-party quantum Byzantine consensus protocol, the full quantum one-way function verifies the honesty of the participants in both list distribution phase and agreement phase. Security analysis demonstrates that the proposed multi-party quantum Byzantine consensus protocol is secure against quantum attacks and the dishonest behaviors of participants.

We show that a bipartite Gaussian quantum system interacting with an external Gaussian environment may possess a unique Gaussian entangled stationary state and that any initial state converges toward this stationary state. We discuss dependence of entanglement on temperature and interaction strength and show that one can find entangled stationary states only for low temperatures and weak interactions.

One of the notable applications of quantum computing is in cryptography. However, quantum apparatus is still costly at this time. In practicality, some users may not have full quantum capabilities. Boyer et al. in 2007 proffered a semi-quantum key distribution scheme, in which one participant is a quantum user, and the other participant is a classical user. The classical user has limited quantum capabilities. In 2021, Chang et al. proffered an authenticated semi-quantum key distribution (ASQKD) scheme. However, in the Chang et al. scheme, an authenticated classical channel is assumed to be pre-established between a quantum user and a classical user. Once the authenticated classical channel is not available in communication environments, the scheme will be vulnerable to attacks. An ASQKD scheme without authenticated classical channel is more sutable for semi-quantum environments. Therefore, we propose a more secure authenticated semi-quantum key distribution scheme without authenticated classical channel for semi-quantum environments. Our scheme only uses single photons to achieve proven security. In our scheme, the semi-quantum environment contains a quantum user and a classical user. The provable security analysis of our scheme is provided. Our scheme can withstand reflecting attacks and impersonation attacks. We also show the proposed scheme can provide the robustness against collective attacks. That is to say, when there is a collective attack on our scheme, any unitary operator from the attacker to acquire useful information will be detected. Moreover, we also do the performance evaluation and comparison with other relevant schemes. The results show that our scheme has the following preferable properties: high qubit efficiency, no quantum memory (storage) required, no classical channel required, and secret Hash function for the session key. Therefore, our proposed scheme in semi-quantum environments is a secure scheme.

Parrondo’s paradox refers to an unexpected effect when some combination of biased quantum walks shows a counterintuitive inversion of the bias direction. To date this effect was studied in the case of one-dimensional discrete-time quantum walks with deterministic sequences of two or more quantum coins and one shift operator. In the present work, we show that Parrondo’s paradox may also occur for one coin and two different shift operators which create deterministic periodic or aperiodic sequences. Moreover, we demonstrate how Parrondo’s paradox affects the time evolution of the walker-coin quantum entanglement for this kind of quantum walks.

We present an electrically driven scheme for spin–photon quantum interfaces used in quantum networks. Through modulating the motion of a nano-cantilever with voltages, optomechanical coupling and spin–mechanical coupling can be exponentially enhanced simultaneously. Numerical simulations show that by applying well-designed voltages high-fidelity quantum interface operations such as generation and absorption of a single photon with a known wave packet are within the reach of current techniques.

In this work, we present a new model of the Discrete-Time Open Quantum Walk (DTOQW) applicable to an arbitrary graph, thereby going beyond the case of quantum walks on regular graphs. We study the impact of noise in the dynamics of quantum walk by applying Kraus operators of different dimensions which are constructed using the Weyl operators. The DTOQW employs these Kraus operators as its coin operators. The walker dynamics are studied under the impact of non-Markovian amplitude damping, dephasing and depolarizing noise channels. We also implement the walk on various graphs, including path graphs, cycle graphs, star graphs, complete graphs, complete bipartite graphs, etc. We gauge the dynamics by computing coherence and fidelity at different time steps, taking into account the influence of noise. Furthermore, we compute the probability distribution at different time-steps for the above noises, which represents the availability of the quantum walker at different vertices of the graph.

Neural networks provide a prospective tool for error mitigation in quantum simulation of physical systems. However, we need both noisy and noise-free data to train neural networks to mitigate errors in quantum computing results. Here, we propose a physics-motivated method to generate training data for quantum error mitigation via neural networks, which does not require classical simulation and target circuit simplification. In particular, we propose to use the echo evolution of a quantum system to collect noisy and noise-free data for training a neural network. Under this method, the initial state evolves forward and backward in time, returning to the initial state at the end of evolution. When run on a noisy quantum processor, the resulting state will be affected by the quantum noise accumulated during evolution. Having a vector of observable values of the initial (noise-free) state and the resulting (noisy) state allows us to compose training data for a neural network. We demonstrate that a feed-forward fully connected neural network trained on echo-evolution-generated data can correct results of forward-in-time evolution. Our findings can enhance the application of neural networks to error mitigation in quantum computing.