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Physical review. B./Physical review. B

Manipulation of asymmetric steering and periodic entanglement in cavity magnetomechanics induced by chiral exceptional points

Zhonghui Yuan, Yan Xia, Yongyuan Jiang, Jie Song

Published Jan 23, 2025• 1 citation
Publisher

Abstract

We study the periodic entanglement and asymmetric steering at exceptional points for a non-Hermitian cavity magnetomechanics system in which exceptional points (EPs) emerge periodically by controlling the relative phase angle of the nanoparticles. First, we analyze this hybrid system and identify parametric regimes where different types of entanglement and steering are enhanced. Entanglement and steering can be significantly enhanced due to the external control method and are thus more robust to thermal noises. This provides an active method to manipulate the asymmetry of steering instead of adding asymmetric losses or noises to subsystems at the cost of reducing steering ability. Moreover, the relative phase angle (RPA) not only enhances the strength of entanglement but also increases the domain of entanglement over a wider space of detunings compared to a system in which no RPA is present. Another important consequence of the RPA is that it controls the directivity of quantum steering. Specifically, steering reaches a maximal value at EPs as well, and we can get rich properties of Einstein-Podolsky-Rosen steering; e.g., the asymmetry of the overall state is stepwise, including one-way quantum steering, no-way quantum steering, and two-way quantum steering. We believe that the presented scheme is a step forward in realizing robust quantum entanglement using current technology. Our results indicate that cavity magnetomechanics systems could provide a promising platform for the study of macroscopic quantum phenomena.

DOI
10.1103/physrevb.111.014433

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We study the periodic entanglement and asymmetric steering at exceptional points for a non-Hermitian cavity magnetomechanics system in which exceptional points (EPs) emerge periodically by controlling the relative phase angle of the nanoparticles. First, we analyze this hybrid system and identify parametric regimes where different types of entanglement and steering are enhanced. Entanglement and steering can be significantly enhanced due to the external control method and are thus more robust to thermal noises. This provides an active method to manipulate the asymmetry of steering instead of adding asymmetric losses or noises to subsystems at the cost of reducing steering ability. Moreover, the relative phase angle (RPA) not only enhances the strength of entanglement but also increases the domain of entanglement over a wider space of detunings compared to a system in which no RPA is present. Another important consequence of the RPA is that it controls the directivity of quantum steering. Specifically, steering reaches a maximal value at EPs as well, and we can get rich properties of Einstein-Podolsky-Rosen steering; e.g., the asymmetry of the overall state is stepwise, including one-way quantum steering, no-way quantum steering, and two-way quantum steering. We believe that the presented scheme is a step forward in realizing robust quantum entanglement using current technology. Our results indicate that cavity magnetomechanics systems could provide a promising platform for the study of macroscopic quantum phenomena.
We propose a method to achieve a coherent switch of optomagnonic entanglement in a cavity optomagnonic system with non-Hermitian coupling. The strength of photon-photon and photon-magnon entanglement can be controlled by tuning the relative phase angle of two nanoparticles and optimizing the detuning of two optical modes. We show that the bipartite entanglement is significantly enhanced by selecting a suitable optomagnonics coupling strength in the presence of the exceptional points (EPs). The relative phase not only enhances the entanglement strength but also increases the entanglement domain over a wide range of detuning compared to the Hermitian system. By manipulating the system toward or away from EPs, versatile tunability of the tripartite entanglement, mean photon, and magnon numbers can be achieved. Additionally, the direction of asymmetric transmission can also be well tuned in a highly asymmetric way via non-Hermitian coupling. The study of controlled entanglement may provide the theoretical basis and reference for the research and development of new tunable quantum devices.
Based on the phenomenon of exceptional points (EPs) in the optomechanically induced mechanical P T -symmetric binary and ternary systems, we propose a mechanism to generate the perfect one-way quantum steering between two totally symmetric modes, respectively. By investigating the quantum steering behavior in the close vicinity of EP, we find that the optimal one-way quantum steering can be successfully generated at the EP in the P T -symmetric binary mechanical system. When pushing the system towards the EP, we show that not only is the broadest region of the one-way quantum steering achieved, but the robustness against the thermal noise can be significantly enhanced. In addition, the direction of the one-way quantum steering can be precisely controlled only by altering the sign of the detuning of the cavity field. What’s more, we analyze the mean populations of the involved modes to further support our findings and find that the occurrence of the one-way quantum steering depends mainly on the difference in the populations between the two target modes. We also successfully extend our findings to the high-order EP, and the desired one-way quantum steering can still be generated in the P T -symmetric ternary mechanical system when it operates at the EP. Our scheme opens up an alternative manipulation method to explore the various novel quantum effects exploiting the EPs and has significant potential applications in quantum nonreciprocal devices.
We propose a hybrid cavity magnomechanical system to realize and transfer the bipartite entanglements and Einstein-Podolsky-Rosen (EPR) steerings between magnons, photons, and phonons in the regime of stability of the system. As a parity-time-symmetric-like structure exhibiting the natural magnetostrictive magnon-phonon interaction, our passive-active cavity system can be explored to enhance the robust distant quantum entanglement and generate the relatively obvious asymmetric (even directional) EPR steering that is useful for the task with the highly asymmetric trusts of the bidirectional local measurements between two entangled states. It is of great interest that, based on such a tunable magnomechanical system, the perfect transfer between near and distant entanglements and steerings of different mode pairs is realized by adjusting the coupling parameters; in particular, we propose a perfect transfer scheme of steerings. These transferring processes suggest indeed an alternative method for quantum information storage and manipulation. In addition, the entanglements and steerings can also be exchanged between different mode pairs by adjusting the detunings between different modes. This work may provide a potential platform for distant and asymmetric quantum modulation.
Abstract We propose to generate and control stationary one-way steering with strong entanglement between photon and magnon modes by the cooperative effect of coherent coupling and dissipative coupling. Due to the combination of two couplings, the system becomes a parity-time-like symmetric non-Hermitian system, and two exceptional points (EPs)-like appear in the real and imaginary parts of the eigenvalues. We demonstrate that the especially obvious quantum entanglement and perfect one-way steering can be obtained around two EPs-like. The continuous variable entanglement and steering produced by this cooperative effect show stronger robustness to environment temperature and system dissipation than that induced by nonlinearity. The one-way steering directivity can be controlled by the relative phase of cooperative dissipation and the frequency detuning of the magnon mode. Our work shows the controllability advantage of the open cavity magnonic system and may open up a platform for the generation of stationary one-way steering.
We present a phase control method for a general three-mode system with closed-loop coupling that drives the system into an entangled steady state and produces directional steering between two completely symmetric modes via quantum interference effects. In the scheme, two modes are coupled with each other both by a direct binary interaction and by an indirect interaction through a third intermediate damping mode, creating interference effects determined by the relative phase between the two physical interaction paths. By calculating the populations and correlations of the two modes, we show that, depending on the phase, two modes can be prepared into an entangled steady state with asymmetric and directional steering even if they possess completely symmetric decoherence properties. Meanwhile, entanglement and steering can be significantly enhanced due to constructive interference and thus are more robust to thermal noises. This provides an active method to manipulate the asymmetry of steering instead of adding asymmetric losses or noises to subsystems at the cost of reducing steerability. Moreover, we show that the interference effects can also enhance and control the correlations between other pairs of modes in the loop with opposite phase-dependent behavior, indicating monogamy constraints for distributing correlations among multiple parties. The present model could be applied in cavity optomechanical systems or in antiferromagnets where all components can mutually interact.
We propose a scheme to enhance entanglement and asymmetric steering between two mechanical oscillators in an optomechanical system with coherent feedback control. In the system, an optical cavity interacts with two mechanical oscillators and an auxiliary cavity whose output field is fed back into the input port of the optical cavity via a feedback loop. Due to the coherence between the auxiliary cavity and feedback, we derive the effective decay rate and a nonzero frequency shift of the optical cavity. Consequently, the induced beam-splitter-type and parametric-type interactions between the two mechanical oscillators are modulated, which leads to the enhancement of entanglement and the generation of asymmetric steering even if the two mechanical oscillators possess identical decoherence properties. And the direction of asymmetric steering can be controlled by tuning the jumping phase between two cavities and optimizing the ratio of drive asymmetry. In contrast to the method of adding losses or noises to one subsystem at the cost of reducing steerability, this scheme provides an active way to achieve enhanced asymmetric steering. Furthermore, the steady-state and dynamical entanglement and asymmetric steering can be generated in the unresolved-sideband regime, which is friendly for experimental implementation.