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Annalen der Physik

Improving Atom–Mirror Entanglement and Mechanical Squeezing in a Modulated Optomechanical System

Jin‐Liang Guo, Lele Zhai

Published Jan 6, 2022• 6 citations
Publisher

Abstract

Abstract In this paper, the macroscopic quantum entanglement and squeezing in an unresolved‐sideband atom‐optomechanical system with a modulated optical parametric amplifier (OPA) inside the cavity are studied. Increasing the parametric gain of the OPA, the quantum‐classical correspondence between the atom‐mirror entanglement and classical nonlinear dynamics can be found. The critical point where the system experiences the transition from periodic oscillation to period‐doubling motion can be characterized by the singularity of the atom–mirror entanglement. Furthermore, the dependence of the atom–mirror entanglement and mechanical squeezing on the detuning and the parametric gain of the OPA as well as the environment temperature are investigated in detail. It is found that the atom‐mirror entanglement can be enhanced and the mechanical squeezing can be generated by modulating the OPA.

DOI
10.1002/andp.202100445

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Abstract A novel and efficient method is proposed for generating mechanical squeezing in a double‐cavity optomechanical system by introducing an optical parametric amplifier (OPA) with pump modulation (PM). The combined effects of periodic amplitude modulation of the driving laser and the OPA enable mechanical squeezing in both the resolved‐sideband and unresolved‐sideband regimes, with significantly enhanced squeezing observed in the resolved‐sideband regime. The individual contributions of the OPA and PM to mechanical squeezing is systematically investigated, with results indicating that PM plays a more dominant role. Additionally, the proposed scheme demonstrates excellent robustness against environmental thermal noise. These findings highlight the potential of this approach for advancing quantum precision measurements and exploring macroscopic quantum phenomena.
Cavity optomechanical systems involving an optical parametric amplifier (OPA) can exhibit rich classical and quantum dynamical behaviors. By simply modulating the frequency of the laser pumping the OPA, we find two interesting parameter regimes, with one of them enabling us to study quantum-classical correspondence in system dynamics, while there exist no classical counterparts of the quantum features for the other. For the detuning of the laser pumping around the mechanical frequency, as the parametric gain of OPA increases to a critical value, the classical dynamics of the optical or mechanical modes can experience a transition from the regular periodic oscillation to a period-doubling motion, in which case the light-mechanical entanglement can be well studied by the logarithmic negativity and can manifest the dynamical transition the classical nonlinear dynamics. In addition, the optomechanical entanglement shows a second-order transition characteristic at the critical parametric gain. For the laser detuning being about twice the mechanical frequency, the kind of normal mode splitting comes up in the laser detuning dependence of optomechanical entanglement, which is induced by the squeezing of the optical and mechanical hybrid modes and finds no classical correspondence. The OPA-assisted optomechanical systems therefore offer a simple way to study and exploit quantum manifestations of classical nonlinear dynamics.
Abstract A hybrid optomechanical system which is composed of an atomic ensemble and a standard optomechanical cavity driven by a periodically modulated external laser field is investigated. Based on the simple periodic modulation forms of the driving amplitude and effective optomechanical coupling, respectively, the atom‐mirror entanglement is discussed in detail. It is found that the maximum of the entanglement in the unresolved‐sideband regime can be further enhanced compared with the non‐modulation regime. On the other hand, we find that the introduction of the atomic ensemble permits the mechanical squeezing induced by the periodic amplitude modulation can be successfully generated even in the unresolved‐sideband regime. Due to the self‐cooling mechanism constructed by the atomic ensemble, the mechanical squeezing scheme no longer requires the extra precooling technologies.
We report an efficient mechanism to generate mechanical entanglement in a two-cascaded cavity optomechanical system with optical parametric amplifiers (OPAs) inside the two coupled cavities. We use the especially tuned OPAs to squeeze the hybrid mode composed of two mechanical modes, leading to strong macroscopic entanglement between the two movable mirrors. The squeezing parameter as well as the effective mechanical damping are both modulated by the OPA gains. The optimal degree of mechanical entanglement therefore depends on the balanced process between coherent hybrid mode squeezing and dissipation engineering. The mechanical entanglement is robust to strong cavity decay, going beyond simply resolved sideband regime, and is resistant to reasonable high thermal noise. The scheme provides an alternative way for generating strong macroscopic entanglement in cascaded optomechanical systems.
Abstract We investigate the effect of a degenerate optical parametric amplifier (OPA) placed inside an optomechanical cavity on the steady-state entanglement of two cavity modes, which jointly interact with a mechanical resonator. Two cavity modes are, respectively, driven at the red and blue sideband associated with the mechanical resonator, which generates entanglement between them in the limit of resolved sideband. The OPA gives rise to single-mode squeezing of the cavity fields, which results in significant improvement of the two-mode entanglement. It is found that an optimal nonlinear gain of the OPA exists, depending on the system temperatures, which yields the maximum entanglement. The improvement is particularly remarkable for the system at cryogenic temperatures.