Quantum Information Processing最新文献

Realignment operation has a significant role in detecting bound as well as free entanglement. Just like partial transposition, it is also based on permutations of the matrix elements. However, the physical implementation of realignment operation is not known yet. In this paper, we address the problem of experimental realization of realignment operation, and to achieve this aim, we propose a theoretical proposal for the same. We first show that after applying the realignment operation on a bipartite state, the resulting matrix can be expressed in terms of the partial transposition operation along with column interchange operations. We observed that these column interchange operations forms a permutation matrix which can be implemented via SWAP operator acting on the density matrix. This mathematical framework is used to exactly determine the first moment of the realignment matrix experimentally. This has been done by showing that the first moment of the realignment matrix can be expressed as the expectation value of a SWAP operator which indicates the possibility of its measurement. Further, we have provided an estimation of the higher-order realigned moments in terms of the first realigned moment and thus pave a way to estimate the higher-order moments experimentally. Next, we develop moment-based entanglement detection criteria that detect positive partial transpose entangled states as well as negative partial transpose entangled states. Moreover, we define a new matrix realignment operation for three-qubit states and have devised an entanglement criteria that is able to detect three-qubit fully entangled states. We have developed various methods and techniques in the detection of bipartite and tripartite entangled states that may be realized in the current technology.

We explore the relationship between entropy and quantum measurements and present a variational algorithm for preparing statistical ensembles on quantum computers using mid-circuit measurements. This algorithm optimizes both the entropy and variational parameters describing the state to obtain the minimum free energy of quantum systems in thermal equilibrium with some external heat bath. We demonstrate our algorithm on IBM-Q Lagos.

We investigate the distinguishability of lattice states by local operations and classical communication (LOCC) in ({mathbb {C}}^{p^{r}}otimes {mathbb {C}}^{p^{r}}), where p is a prime. Firstly, for all the lattice matrices, we present that there are (prod _{a=1}^{r}(p^{a}+1)) number of distinct maximal commuting sets. Secondly, we give a criterion to determine the local discrimination of lattice states via adjacent matrix. The previous results (Phys Rev A 92:042320, 2015; Phys Scr 98:115102, 2023) can be covered by our result. Finally, we give a sufficient condition for LOCC indistinguishability of (p^{r}) lattice states.

Quantum secure direct communication is a significant branch of quantum cryptography. Recently, a quantum secure direct communication scheme based on intermediate-basis was proposed (Liang et al. in Front Phys 18(5):51301, 2023 https://doi.org/10.1007/s11467-023-1284-4). It is believed that the scheme can improve the efficiencies of security detection and information encoding by utilizing the intermediate-basis. However, this paper points out two serious problems with the aforementioned scheme. Firstly, it fails to utilize two distinct bases since the intermediate-basis is merely a variant of the Bell basis. Accordingly, the quantum secure direct communication scheme based on intermediate-basis cannot achieve the promised high efficiency. Secondly, even if the intermediate-basis is substituted with another quantum basis, the modified quantum secure direct communication scheme cannot achieve the promised high efficiency because the receiver cannot correctly decode the secret message from the final entangled pairs. It is crucial to design correct and efficient quantum secure direct communication protocols. This work can remind the developers of quantum secure direct communication to avoid such pitfalls when they enhance the robustness and efficacy of their schemes.

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.