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Chinese Physics B

Nonreciprocal coupling induced entanglement enhancement in a double-cavity optomechanical system

Yuan Yuan Liu, Zhi‐Ming Zhang, Jun‐Hao Liu, Jindong Wang, Ya‐Fei Yu

Published Apr 6, 2022• 9 citations
Publisher

Abstract

We investigate the quantum entanglement in a double-cavity optomechanical system consisting of an optomechanical cavity and an auxiliary cavity, where the optomechanical cavity mode couples with the mechanical mode via radiation-pressure interaction, and simultaneously couples with the auxiliary cavity mode via nonreciprocal coupling. We study the entanglement between the mechanical oscillator and the cavity modes when the two cavities are reciprocally or nonreciprocally coupled. The logarithmic negativity E n ( 1 ) ( E n ( 2 ) ) is adopted to describe the entanglement degree between the mechanical mode and the optomechanical cavity mode (the auxiliary cavity mode). We find that both E n ( 1 ) and E n ( 2 ) have maximum values in the case of reciprocal coupling. By using nonreciprocal coupling, E n ( 1 ) and E n ( 2 ) can exceed those maximum values, and a wider detuning region where the entanglement exists can be obtained. Moreover, the entanglement robustness with respect to the environment temperature is also effectively enhanced.

DOI
10.1088/1674-1056/ac6499

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We investigate the quantum entanglement in a double-cavity optomechanical system consisting of an optomechanical cavity and an auxiliary cavity, where the optomechanical cavity mode couples with the mechanical mode via radiation-pressure interaction, and simultaneously couples with the auxiliary cavity mode via nonreciprocal coupling. We study the entanglement between the mechanical oscillator and the cavity modes when the two cavities are reciprocally or nonreciprocally coupled. The logarithmic negativity E n ( 1 ) ( E n ( 2 ) ) is adopted to describe the entanglement degree between the mechanical mode and the optomechanical cavity mode (the auxiliary cavity mode). We find that both E n ( 1 ) and E n ( 2 ) have maximum values in the case of reciprocal coupling. By using nonreciprocal coupling, E n ( 1 ) and E n ( 2 ) can exceed those maximum values, and a wider detuning region where the entanglement exists can be obtained. Moreover, the entanglement robustness with respect to the environment temperature is also effectively enhanced.
In this work, we investigate a theoretical study of the stationary entanglement of an optomechanical system by adding a Kerr medium in the cavity where the mechanical resonator is perturbatively connected to an auxiliary qubit. The degree of entanglement between the cavity field and the mechanical system is measured by using the logarithmic negativity. We show that optomechanical entanglement is decreased by Kerr interaction due to photon blockage enhanced by mirror–qubit coupling, we also show that this enhancement is influenced by the temperature. In addition, we find that, in the presence of the mirror–qubit coupling, entanglement can arise with far weaker optomechanical coupling. The proposed scheme shows that the presence of the mirror–qubit coupling and Kerr medium is an effective control for an optomechanical system.
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.
We consider a dissipative cavity optomechanical system which couples to an auxiliary cavity with a high-quality factor and is driven by an amplitude-modulated laser field. Due to the introduction of the auxiliary cavity, we find that the steady-state mechanical squeezing can be enhanced compared to the case without an auxiliary cavity and the so-called 3 dB limit can also be broken in the resolved-sideband regime. Moreover, the squeezing can also be achieved even in the unresolved-sideband regime. We study the optomechanical entanglement in the presented system. It is found that the enhanced entanglement can be obtained by introducing the auxiliary cavity, and the entanglement can also be generated in the unresolved-sideband regime for appropriate system parameters. Numerical results show that the presented schemes have strong robustness against the thermal noise acting on the mechanical mode.
The generation of quantum entanglement in macroscopic systems remains a longstanding challenge. In this paper, we study theoretically the stationary entanglement of the two remote mechanical oscillators in a two-cascaded-cavity optomechanical system with a degenerate optical parametric amplifier (OPA) inside the first cavity. The two cavity modes in each cavity are driven at the red- and blue-sideband frequencies. The logarithmic negativity is used to quantify the amount of the stationary mechanical entanglement. We find that the stationary mechanical entanglement depends on the parametric gain and phase of the OPA, the input laser powers, the cavity decay rates, and the temperature of the environment. We show that it is possible to enhance the stationary mechanical entanglement by the use of the OPA, and the optimal enhancement of the stationary mechanical entanglement happens at the parametric phase 𝜋 / 2 of the OPA. At lower temperatures, the OPA exhibits a more significant improvement effect on the stationary mechanical entanglement.
Radiation pressure in an optomechanical system can be used to generate various quantum entanglements between the subsystems. Recently, one paid more attention to the study of quantum entanglement in an optomechanical system. Here in this work, we study the properties of output entanglement between two filtered output optical fields by the logarithmic negativity method in a double-cavity optomechanical system. Our calculations show that the decay rate of the mechanical resonator, the bandwidth of filter function, and non-equal-coupling will evidently affect the value of the output entanglement. In particular, under the parameters of equal-coupling and zero filter bandwidth, the output entanglement in the vicinity of resonant frequency (=0 in the rotating frame) will decease with mechanical decay rate increasing. But under the parameters of equal-coupling and non-zero filter bandwidth, the output entanglement will be suppressed if the center frequency of output field is in the vicinity of the resonant frequency. However, the output entanglement can be enhanced if we adopt a non-equal-coupling to counteract the suppression effect of the filter bandwidth. Furthermore, we find that there are three peaks in the whole center frequency domain of the output field if we adopt strong non-equal-coupling. This is because the normal mode of Hamiltonian Hint will split into three normal modes in this case. Our results can also be used in other parametrically coupled three-mode bosonic systems and may be applied to realizing the state transfer process and quantum teleportation in an optomechanical system.
In this paper, the optical nonreciprocal phenomena in double optomechanical systems with quadratic coupling are studied. Our model belongs to an optomechanical system in which three coupling modes coexist, that is, the two cavity fields are coupled with the mechanical oscillator at the same time and the couplings are in the form of quadratic interactions. In addition, there is a linear coupling mode between the two cavity fields. In the entire system, each cavity field is effectively coupled by a control field and a probe field simultaneously. The expression of the transmission coefficient of the probe field is obtained by solving the dynamic evolution equation satisfied by the system. Using numerical analysis, we analyze the change in transmission coefficient of the probe field under the conditions of different physical parameters. The results show that we can realize optical nonreciprocal transmission in this system. Appropriate choices about physical parameters can achieve perfect nonreciprocity. Our theoretical scheme to realize optical nonreciprocal transmission in a double optomechanical system provides a theoretical basis for optical circulators, cyclic amplifiers and directional amplifiers.