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Advanced Quantum Technologies

Enhancement of Nonreciprocal Entanglement and Transmission via Phase‐Dependent Unidirectional Coupling

Nan Wang, Tingting Dong, Shi‐Yan Li, Ning Yuan, Lin Yu, Ai‐Dong Zhu

Published Aug 12, 2024• 3 citations
Publisher

Abstract

Abstract The nonreciprocal property of quantum systems is crucial for chiral quantum networks. In this study, a phase‐controlled scheme is proposed to enhance the nonreciprocal quantum entanglement and optical transmission in a cavity optomechanical system by introducing a phase‐dependent unidirectional coupling between two whispering‐gallery‐mode (WGM) resonators. The Sagnac effect induced by the spinning resonator generates nonreciprocity, while the interference effect between direct evanescent coupling and indirect phase‐dependent unidirectional coupling significantly enhances entanglement under the anti‐Stokes sideband. For specific coupling phases, ideal nonreciprocity can be achieved in both entanglement and transmission. The proposed phase‐controlled nonreciprocity presented offers an effective strategy for constructing a unidirectional quantum channel and implementing an optical diode in chiral quantum networks, thereby opening up new possibilities for applications in quantum technologies.

DOI
10.1002/qute.202400224

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Abstract The nonreciprocal property of quantum systems is crucial for chiral quantum networks. In this study, a phase‐controlled scheme is proposed to enhance the nonreciprocal quantum entanglement and optical transmission in a cavity optomechanical system by introducing a phase‐dependent unidirectional coupling between two whispering‐gallery‐mode (WGM) resonators. The Sagnac effect induced by the spinning resonator generates nonreciprocity, while the interference effect between direct evanescent coupling and indirect phase‐dependent unidirectional coupling significantly enhances entanglement under the anti‐Stokes sideband. For specific coupling phases, ideal nonreciprocity can be achieved in both entanglement and transmission. The proposed phase‐controlled nonreciprocity presented offers an effective strategy for constructing a unidirectional quantum channel and implementing an optical diode in chiral quantum networks, thereby opening up new possibilities for applications in quantum technologies.
Abstract A scheme is proposed to enhance the optomechanical entanglement nonreciprocally in a spinning cavity optomechanical system driven by a periodically modulated pump field. Based on the Sagnac effect induced by the resonator's spinning, the direction‐dependent frequency shifts are introduced to the counterpropagating optical modes. By combining the Sagnac effect with periodic pump modulation, the optomechanical entanglement can be enhanced nonreciprocally by a factor of about 1.67. It is shown that the negative effect of the backscattering losses on nonreciprocal entanglement enhancement can be eliminated by spinning the resonator. Meanwhile, the enhanced entanglement exhibits strong robustness against thermal noise, surviving even at environmental temperature up to 0.99 K. This work is expected to promote the development of nonreciprocal quantum networks and quantum control techniques.
Abstract A scheme is proposed for generating and enhancing stable nonreciprocal entanglement in a spinning cavity magnomechanical system. The key components of this scheme include a ferromagnetic yttrium iron garnet sphere and a whispering gallery mode resonator supporting two counter‐propagating modes. To further optimize the performance of the system, a coherent feedback loop is introduced to reinject the dissipated energy back into the system. This not only provides an additional coupling path for the system but also effectively avoids introducing additional noise caused by measurement. The design significantly enhances both bipartite entanglement and genuine tripartite entanglement. Meanwhile, by spinning the resonator, the cavity modes experience Fizeau drag due to the optical Sagnac effect, thereby achieving nonreciprocal entanglement, which is crucial for applications such as unidirectional quantum communication channels. Additionally, the research demonstrates that even in the presence of backscattering, the entangled state can still recover significantly, highlighting the robustness of entanglement under photon backscattering. This work provides an effective method to enhance and protect quantum resources and holds important application potential for applications in quantum information processing based on magnonics.
Abstract Quantum entanglement between distant massive mechanical oscillators is an important resource in sensitive measurements and quantum information processing. We achieve the nonreciprocal mechanical entanglement in a compound optomechanical device consisting of two mechanical oscillators and a spinning whispering-gallery mode (WGM) optical microresonator. It is found that obvious nonreciprocal mechanical entanglement emerges in this system in the presence of the Sagnac effect which is induced by the rotation of the WGM resonator, and the nonreciprocal region can be controlled by tuning the angular velocity of the rotation. The nonreciprocity originates from the breaking of the time-reversal symmetry of this multimode system due to the presence of the Sagnac effect. The optomechanical coupling and the mechanical interaction provide cooling channels for the first and second mechanical oscillators, respectively. Two mechanical oscillators can be cooled simultaneously. The simultaneous cooling and the mechanical coupling of two mechanical oscillators ensure the generation of mechanical entanglement. Furthermore, an optimal mechanical entanglement can be achieved when the moderate optical frequency detuning and the driving power are chosen. The thermal noise of the mechanical environment has a negative effect on mechanical entanglement. Our scheme provides promising opportunities for research of quantum information processing based on phonons and sensitive measurements.
Abstract A method is proposed to simultaneously achieve nonreciprocal entanglement and nonreciprocal dipole blockade in a spinning cavity QED system, where two qubits are subjected to dipole–dipole interaction and coupled to a cavity mode. It is found that the entanglement and the dipole blockade prominently manifest in a chosen direction, while completely vanishing in the other. Remarkably, the perfect nonreciprocal entanglement and dipole blockade can be generated. This nonreciprocity results from Sagnac effect, which leads to different quantum interference effects in the opposite direction. The work provides an all‐optical manipulation method for controlling the entanglement and the dipole blockade, which may have potential applications in the implementation of chiral networks and backaction‐immune quantum sensors.
We propose a scheme to create nonreciprocal entanglement in a spinning cavity magnomechanical system. The setup comprises a whispering gallery mode resonator with two counterpropagating modes, simultaneously coupled to yttrium iron garnet. By spinning the resonator, the counterpropagating modes undergo an opposite Fizeau drag caused by the optical Sagnac effect. We show that in a spinning resonator, the cavity-magnon-phonon modes get entangled along a chosen direction while remaining fully uncorrelated in the other. The degree of nonreciprocity is determined by the drive detuning and the spinning velocity of the resonator. Our work provides a different route to achieve chiral control of quantum entanglement involving magnon-photon-phonon modes.
Ultrahigh nonreciprocal transmission has been achieved in a cavity-magnon system, which consists of two whispering gallery modes (WGMs) and a single magnon mode within a magnetic insulator yttrium iron garnet sphere. The nonreciprocal frequency shift induced by the Sagnac effect enables unidirectional transmission of an input field, while suppressing propagation in the opposite direction, thereby facilitating nonreciprocal optical transmission. Within experimentally accessible parameter regimes, the optical isolation ratio can exceed 40 dB, representing the highest isolation ratio reported to date. Furthermore, applying squeezing to the magnon mode further enhances this isolation performance. Additionally, the directionality of light isolation can be reversed simply by modifying the rotation of the WGM cavity. These findings offer promising prospects for developing high-performance, tunable, and compact optical nonreciprocal devices.