Advanced quantum technologies最新文献

We investigate how parity-time ($�\mathrm{PT}$) symmetry influences photon blockade in an atom-coupled dual-cavity quantum electrodynamics (QED) system, with a focus on distinguishing the underlying mechanisms. Statistical analysis demonstrates that photon blockade exhibits qualitatively distinct behaviors in the $�\mathrm{PT}$-symmetric and symmetry-broken phases, thereby providing a clear signature of the $�\mathrm{PT}$ phase transition. In this $�\mathrm{PT}$-symmetric structure, the two-level atom provides the required nonlinearity, while cavity-cavity coupling under $�\mathrm{PT}$-symmetric control cooperatively enhances photon antibunching, leading to simultaneous photon blockade in both the passive and the active cavities. These phenomena are comprehensively analyzed using both analytical solutions of the Schrödinger equation and numerical simulations of the master equation. Comparisons with non-$�\mathrm{PT}$-symmetric configurations reveal that $�\mathrm{PT}$ symmetry significantly enhances photon antibunching, mean photon number and promotes cooperative blockade behavior across both cavities. In contrast to conventional photon blockade schemes, our approach remains effective under weak coupling and weak nonlinearity conditions, offering a robust and tunable pathway toward realizing high-performance single-photon sources in non-Hermitian quantum systems.

Variational quantum algorithms (VQAs) have emerged as a promising approach for achieving quantum advantage on current noisy intermediate-scale quantum devices. However, their large-scale applications are significantly hindered by optimization challenges, such as the barren plateau (BP) phenomenon, local minima, and numerous iteration demands. In this work, we leverage denoising diffusion models (DM) to address these difficulties. The DM is trained on a few data points in the Heisenberg model parameter space and then can be guided to generate high-performance parameters for parameterized quantum circuits (PQCs) in variational quantum eigensolver (VQE) tasks for general Hamiltonians. Numerical experiments demonstrate that DM-parameterized VQE can explore the ground-state energies of Heisenberg models with parameters not included in the training dataset. Even when applied to previously unseen Hamiltonians, such as the Ising and Hubbard models, it can generate the appropriate initial state to achieve rapid convergence and mitigate the BP and local minima problems. More interestingly, we discover the possibility of parameter transferability and extrapolation among different quantum many-body Hamiltonians.

Nonreciprocal quantum batteries offer superior charging performance compared to reciprocal quantum batteries. We consider a charger-battery system comprising two optical cavities that interact independently with a third auxiliary cavity. We show that the nonzero dissipation of the auxiliary cavity induces a nonreciprocal exchange of excitations among the charger-battery system. Therefore, by engineering the loss in the auxiliary cavity, we induce a directional energy flow that enhances the charging efficiency. Using numerical and analytical calculations, we show that the steady-state energy stored in the battery significantly exceeds that in the charger. We compare our results with those of the reciprocal cases and demonstrate that our nonreciprocal quantum battery model exhibits a significant charging advantage. We believe that our proposed scheme represents a step forward in cavity-loss engineering, making it a viable approach for nonreciprocal quantum batteries with existing experimental techniques.

Superconducting quantum interference devices (SQUIDs), as the most sensitive solid-state magnetic sensors currently available, play a crucial role in both fundamental science and industrial applications. This review systematically examines the research progress in high-temperature superconducting (HTS) SQUID magnetometers and gradiometers and their possible applications of SQUIDs. By detailing the working principles of DC and RF SQUIDs and reviewing advancements in critical system components—such as sensing elements, cryogenics, and readout electronics—this work lays a solid theoretical and structural foundation for ultra-sensitive magnetic sensing. Furthermore, by describing the properties of various HTS Josephson junctions, their flexibility, and critical points, we aim at highlighting the uniqueness of certain features and the possibility of tuning a variety of physical processes in these junctions. Additionally, it comprehensively summarizes innovative applications in biomedical imaging, geophysical exploration, and industrial non-destructive testing. The innovation of this review lies in constructing a developmental framework for HTS SQUID technology from a complete chain perspective of principles-devices-fabrication processes-applications, providing systematic technical references for researchers in related fields, which has important guiding significance for promoting the practical application of quantum sensing technology.

Quantum entanglement is a crucial resource in quantum information science, applying to quantum key distribution, quantum sensing, and quantum teleportation. However, generating macroscopic quantum entanglement in multimode optomechanical systems, where an optical mode couples to multiple degenerate or near-degenerate vibrational modes, is a challenging task, as the entanglement is suppressed by the dark-mode effect. In this paper, we propose a scheme to generate both bipartite and genuine tripartite entanglement in the system via periodic modulation. First, we consider a two-oscillator optomechanical system in which time-varying voltages applied to the oscillators enable the engineering of coupling pathways between the bright and dark modes, thus breaking the dark-mode effect. Thermal phonons can be extracted by the coupling channels, so that bipartite and tripartite entanglement can be achieved at a nonzero temperature. Furthermore, we extend this scheme to an optomechanical system with $��N�\ge �3�$ oscillators, where the degenerate vibrational modes can entangle with the optical mode. Notably, the macroscopic quantum entanglement we obtain exhibits greater robustness against thermal phonons.