Advanced quantum technologies最新文献

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.

Niobium (Nb) films have emerged as a crucial material in the development of superconducting qubits, which are key components in quantum computing technology. This review provides a comprehensive examination of Nb films from a materials perspective, focusing on their intrinsic properties, fabrication methods/techniques, and their influence on qubit performance, particularly through surface and interface driven loss mechanisms. We discuss the key material properties that are essential for qubit operation. Various deposition techniques for Nb thin films, such as sputtering, evaporation, molecular beam epitaxy, and atomic layer deposition, are explored, alongside their impact on film quality, uniformity, and qubit performance. Additionally, the influence of surface roughness, thin-film thickness, and substrate materials on quantum coherence is analyzed. Challenges such as defects and material degradation in Nb films are reviewed, along with strategies to mitigate these issues. Finally, we present the latest advancements and future directions in Nb film research, including potential improvements to enhance qubit coherence and scalability for large-scale quantum computing systems. Ultimately, a deeper understanding of surface and interface phenomena is essential for pushing the limits of qubit performance and realizing next-generation quantum technologies.

Single-beam optically pumped atomic magnetometers (OPAMs) are promising tools for biomagnetic measurements in nonzero-field environments owing to their high sensitivity and compactness. However, the angle between the external bias magnetic field and the pump light affects the spin polarization of the atomic ensemble, thereby influencing the magnetometer performance and making the optimization of the magneto-optical angle essential. In this study, a spatially resolved steady-state spin polarization model incorporating the magneto-optical angle is established for the first time, and an analytical expression of the spin precession signal under RF magnetic field excitation is derived. It is demonstrated that an optimal angle exists at which the magnetometer exhibits the maximum response and the highest sensitivity, which is experimentally determined to be 26° in our single-beam OPAM. At this angle, the combined influence of the steady-state spin polarization, spin precession projection, transmitted light intensity, and transverse spin relaxation reaches an optimal overall state, leading to a 14% enhancement in sensitivity and a 32% reduction in detection noise compared with the conventional 45° configuration. These findings provide guidance for optimizing the experimental parameters of single-beam OPAMs for weak magnetic signal detection in nonzero-field environments.