Shou Zhang

Nonreciprocity is a key ingredient for realizing chiral quantum networks. We propose a scheme to achieve the nonreciprocal enhancement of bipartite and tripartite entanglement in a hybrid cavity optomechanical (COM) system comprising a χ ⁽²⁾ nonlinear resonator, an atomic ensemble, and a coherent feedback loop. The phase-matching condition of the χ ⁽²⁾ nonlinear crystal confines the OPA-induced directional squeezing to the counterclockwise (CCW) mode, resulting in nonreciprocal quantum entanglement. We find that the synergistic interplay between directional squeezing and coherent feedback not only enhances the nonreciprocal bipartite and tripartite entanglement, but also substantially improves its dissipation tolerance. Our results demonstrate an alternative mechanism for generating and manipulating nonreciprocal quantum correlations in stationary optomechanical platforms. These findings open a promising avenue for quantum information processing, offering a robust platform for the development of nonreciprocal quantum devices.

Optical gyroscopes, which utilize the Sagnac effect and high-precision optical cavities, hold significant potential for inertial navigation and precision measurement. In conventional weakly coupled schemes, however, the relationship between the dip positions of the transmission spectrum and the Hamiltonian eigenvalues breaks down, leading to inaccurate measurements and limiting sensitivity enhancement. To address this limitation, we propose what we believe to be a new mechanism for a highly sensitive optical gyroscope based on quasi-exceptional points (QEPs) in optical dimers. The QEPs manifest as degeneracies in the frequencies of the transmission dips. This mechanism establishes a direct and reliable relationship between spectral splitting and external perturbations. The results indicate that the system responds with high sensitivity to perturbations near the QEPs, following a square-root dependence. By aligning the sensing mechanism with experimentally observable quantities, this QEP-based scheme provides a more reliable approach for high-precision optical gyroscopes compared to the EP-based scheme. Quantum Fisher information analysis demonstrates that the QEP mechanism achieves superior measurement precision even in the presence of quantum noise. The proposed QEP-based sensing scheme provides a new approach to developing high-precision optical gyroscopes and non-Hermitian sensing technologies.

The precise measurement of weak optomechanical coupling is fundamentally limited by the inevitable thermal noise and the stringent parameter control. To overcome these limitations, we propose what we feel is a novel sensing scheme based on self-Kerr nonlinearity. Remarkably, the self-Kerr nonlinearity induced by the Born-Oppenheimer (BO) adiabatic separation between the optical and mechanical modes enables a sensitivity scaling law proportional to g ^−7/3 , which is the source of extraordinary sensitivity to weak optomechanical coupling. By developing an effective indirectly coupled dual-cavity model featuring self-Kerr nonlinearity and applying Gaussian quantum information theory, we demonstrate that a weak optomechanical coupling can be detected with both an excellent signal-to-noise ratio (SNR) and high precision. Specifically, our scheme improves the SNR and precision by several orders of magnitude, surpassing the capabilities of conventional nonlinear response methods. This work elucidates a fundamental mechanism based on self-Kerr nonlinearity for achieving ultra-high sensitivity in non-Hermitian sensors, thereby paving the way for the development of high-performance sensors in anharmonic systems and advancing the field of ultrasensitive quantum metrology.

We propose a scheme to achieve a nonreciprocal thermodynamic device by utilizing the Barnett effect in a cavity magnomechanical system. By adjusting the effective magnon detuning, we achieve the conversion of the two polariton branches characteristics between magnonlike and phononlike, providing a quantum control foundation for the thermodynamic processes. Depending on the selection of different polariton branches, the system can operate as either a quantum heat engine or thermal accelerator. Under red detuning, changing the direction of the static magnetic field to render the Barnett shift positive can enhance the work output, efficiency, and coefficient of performance (COP). Conversely, it will suppress them, thereby realizing a nonreciprocal thermodynamic device. Under weak effective magnon–phonon coupling conditions, there exists an optimal region suitable for the operation of thermodynamic devices. Our scheme provides a path for the nonreciprocal regulation of thermodynamic devices, and this research holds substantial application prospects for designing a high‐performance thermodynamic device in magnetic devices.