Quantum Information Processing最新文献

Future quantum internet relies on large-scale entanglement distribution. Quantum decoherence is a significant obstacle in large-scale networks, which otherwise perform better with multiple paths between the source and destination. We propose a new topology, a connected tree, with a significant number of redundant edges to support multi-path routing of entangled pairs. We qualitatively analyze the scalability of quantum networks to maximum user capacity in decoherence for different topologies. Our analysis shows that thin-connected tree networks can accommodate a larger number of user pairs while maintaining a high-routing environment, resulting in less dependence on quantum memories for routing than distributed lattice or P-2-P topologies, thus leading to robustness against decoherence and better key generation rates among multiple communicating parties in quantum key distribution.

We analyze in detail a procedure of entangling of two singlet–triplet (S–(T_{0})) qubits operated in a regime when energy associated with the magnetic field gradient, (Delta B_{z}), is an order of magnitude smaller than the exchange energy, J, between singlet and triplet states (Shulman et al. in Science 336:202, 2012). We have studied theoretically a single S–(T_{0}) qubit in free induction decay and spin echo experiments. We have obtained analytical expressions for the time dependence of components of its Bloch vector for quasistatic fluctuations of (Delta B_{z}) and quasistatic or dynamical (1/f^{beta })-type fluctuations of J. We have then considered the impact of fluctuations of these parameters on the efficiency of the entangling procedure which uses an Ising-type coupling between two S–(T_{0}) qubits. In particular, we have obtained an analytical expression for evolution of two qubits affected by (1/f^{beta })-type fluctuations of J. This expression indicates the maximal level of entanglement that can be generated by performing the entangling procedure. Our results deliver also an evidence that in the above-mentioned experiment S–(T_{0}) qubits were affected by uncorrelated (1/f^{beta }) charge noises.

We propose a scheme to generate robust bipartite entanglement, genuine tripartite entanglement, and one-way steering in a hybrid cavity electro-optomechanical system with the help of a squeezed vacuum field. The system consists of an optical cavity, a mechanical resonator formed by a thin silicon nitride membrane, and two superconducting microwave circuits. The mechanical resonator is coupled to the optical cavity and two superconducting circuits simultaneously. We find there is steady-state entanglement between different modes and genuine tripartite entanglement among the cavity mode and two microwave modes which are robust against the thermal fluctuations of the mechanical mode. In addition, the robust one-way steering between two microwave modes can be generated by selecting appropriate squeezing parameter. Our scheme may have potential applications in quantum information processing and communication.

Quantum error mitigation is becoming increasingly crucial. We have reformulated the expression of the Pauli channel, termed as the Z-mixed-state expression of the Pauli channel (ZMSEPC). Based on this expression, we have studied the changes of measurement expectation values after composing multiple Pauli channels and proposed related theorems. Afterward, we proposed a method called quantum error mitigation based on the Z-mixed-state expression of the Pauli channel (QEM-ZMSEPC) that can mitigate both quantum gate noise and quantum measurement noise, which offers a lower complexity compared to traditional measurement error mitigation methods. We have conducted experiments for the QEM-ZMSEPC method on classical computers and real quantum computers. The results demonstrate that compared to zero noise extrapolation method, QEM-ZMSEPC has superior error mitigation effects. Furthermore, our experimental results demonstrate the potential of the QEM-ZMSEPC combining other error mitigation techniques such as Pauli twirling. These positive results imply the significance of QEM-ZMSEPC.

Despite the proven security in theory and its potential to achieve high secret key rates, eavesdroppers may crack two-way quantum key distribution (TWQKD) systems by exploiting imperfections of the detection devices that most loopholes exist in, in actual implementations. Lu et al. (Phys. Rev. A 88(4):0443021–044302, 2013) have proved that TWQKD is measurement-device-independent (MDI) security on Bob’s side while assuming ideal detectors on Alice’s side. However, the MDI security proof on Alice’s side is still missing. In this paper, we focus on proving that the TWQKD protocol, secure deterministic communication without entanglement, proposed by Lucamarini and Mancini in 2005 (LM05), is MDI security on both sides of Alice and Bob (fully MDI scenario). First, using a relatively simple method, we give a qubit-based analytical proof that the LM05 is fully MDI security in a depolarizing quantum channel. Then, based on the analytical proof, we derive the expected lower bound of the security formula for it with the reasonable model of finite single-photon sources based on recent experiment progress. Moreover, with the parameters of the current technology, simulation results of the lower bound are presented. It shows that TWQKD can achieve good performances in the fully MDI scenario.

We explore the dynamics of (l_1)-norm of steered quantum coherence (SQC), steered quantum relative entropy (SQRE), and magic resource quantifier (MRQ) in the one-dimensional XY spin chain in the presence of time-dependent transverse magnetic field. We find that the system’s response is highly sensitive to the initial state and magnetic field strength. We show the dynamics of SQC, SQRE, and MRQ revealing the critical point associated with equilibrium quantum phase transition (QPT) of the system. All quantities show maximum at QPT when the initial state is prepared in the ferromagnetic phase. Conversely, they undergo abrupt changes at quantum critical point if the initial state of the system is paramagnetic. Moreover, our results confirm that when quench is done to the quantum critical point, the first suppression (revival) time scales linearly with the system size, and remarkably, its scaling ratio remains consistent for all quenches, irrespective of the initial phase of the system. These results highlight the interplay between the quantum information resources and dynamics of quantum systems away from the equilibrium. Such insights could be vital for quantum information processing and understanding non-equilibrium phenomena in quantum many-body systems.

Advances in quantum information processing can open a way for numerous applications of the processing in various fields of science and technology: communication, precision measurement, computing, nano-scale detectors, and sensors. Classical and various quantum correlations have been studied in real spin 1/2 systems. The nonlocality measures provide a novel classification scheme for bipartite states, highlighting that nonlocality is a quantum resource distinct from other types of quantum correlations. We first studied the temperature and field dependencies of nonlocality measure in the three fictitious spin 1/2 system, which represents a nuclear spin-7/2 placed in magnetic and inhomogeneous electric fields. The relationship between nonlocality and other quantum correlations (entanglement and geometric discord) was studied. The Hamiltonian and spin operators for a spin 7/2 are represented in the basis formed by the Kronecker products of the Pauli matrices. This transformation allows us to represent a spin 7/2 as a system of three coupled fictitious spins 1/2 and, from the quantum information point of view, as an equivalent system of three coupling qubits. Well-developed methods were used to calculate measures of quantum correlations. For example, we consider ⁵⁹Co (spin 7/2) in the compounds [Co(NH₃)₅Cl]Cl₂ and Ca₃Co₂O₆. The interaction between the fictitious spins of ⁵⁹Co nuclei depends on the magnitude and direction of the external magnetic field. Other potential cases of quantum correlations can be realized based on nuclear spins 7/2 in solid-state systems, for instance, such as ⁵¹V, ¹⁶⁵Ho, or ¹²³Sb.

The Poisson equation has many applications across the broad areas of science and engineering. Most quantum algorithms for the Poisson solver presented so far either suffer from lack of accuracy and/or are limited to very small sizes of the problem and thus have no practical usage. In this regard, our previous work (Robson in 2022 IEEE International Conference on Quantum Computing and Engineering (QCE), 2022) showed a proof-of-concept demonstration in advancing quantum Poisson solver algorithm and validated preliminary results for a simple case of (3times 3) problem. In this work, we delve into comprehensive research details, presenting the results on up to (15times 15) problems that include step-by-step improvements in Poisson equation solutions, scaling performance, and experimental exploration. In particular, we demonstrate the implementation of eigenvalue amplification by a factor of up to (2^8), achieving a significant improvement in the accuracy of our quantum Poisson solver and comparing that to the exact solution. Additionally, we present success probability results, highlighting the reliability of our quantum Poisson solver. Moreover, we explore the scaling performance of our algorithm against the circuit depth and width, demonstrating how our approach scales with larger problem sizes and thus further solidifies the practicality of easy adaptation of this algorithm in real-world applications. We also discuss a multilevel strategy for how this algorithm might be further improved to explore much larger problems with greater performance. Finally, through our experiments on the IBM quantum hardware, we conclude that though overall results on the existing NISQ hardware are dominated by the error in the CNOT gates, this work opens a path to realizing a multidimensional Poisson solver on near-term quantum hardware.

Software-based remote memory attestation is a method for determining the state of a remote device without relying on secure hardware. In classical computing devices, the method is vulnerable to proxy and authentication attacks, because an infected device has no means of preventing the leak of its cryptographic secrets. In this paper, we demonstrate how these attacks can be mitigated by making use of quantum effects, while remaining within the class of software-based methods. In particular, we make use of entanglement and the inability of an attacker to clone qubits. Our proposed protocol is lightweight and can be implemented by near-term Quantum Computing techniques. The resulting protocol has the unique feature of resisting collusion between two dishonest devices, one of which has unbounded computational resources.

Extensive studies have been carried out on the characteristics of quantum radar cross section (QRCS) of targets. However, one crucial question related to multi-photon quantum radar cross section (M-QRCS) for targets in the atmospheric medium has not been explored yet. Understanding this question is vital for target detection and identification of quantum radar. This paper presents a universal method to solve M-QRCS in a homogeneous atmospheric medium (HAM-QRCS). The process is based on the photon wave function in a homogeneous atmospheric medium and the interaction mechanism of multi-photon and multiple atoms. It is suitable for analyzing the HAM-QRCS characteristics of targets of arbitrary shapes. The simulation results show that the molecules, particles, and other factors in the atmospheric medium cause the signal photons’ energy to decrease and the propagation direction to change, leading to a decrease in the target return responses. However, in a specific angle range, as the photon number increases, the main lobe and first side lobe structures of the bistatic HAM-QRCS response are enhanced. These findings can be utilized to design target detection strategies and optimize stealth target structures of the quantum radar in the atmospheric medium.