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Chinese Physics B

Coherent feedback ground-state cooling of mechanical resonators assisted by a quantum well

Qinghong Liao, Shi-Hua Ouyang, Shaoping Cheng, Yiping Cheng

Published Feb 5, 2025• 0 citations
Publisher

Abstract

Abstract We theoretically investigate a cooling scheme assisted by a quantum well (QW) and coherent feedback within a hybrid optomechanical system. Although the exciton mode in the QW and the mechanical resonator (MR) are initially uncoupled, their interaction via the microcavity field leads to an indirect exciton-mode–mechanical-mode coupling. The coherent feedback loop is applied by feeding back a fraction of the output field of the cavity through a controllable beam splitter to the cavity’s input mirror. It is shown that the cooling capability is enhanced by effectively suppressing the Stokes process through coupling with the QW. Furthermore, the effect of the anti-Stokes process is enhanced through the application of the coherent feedback loop. This particular system configuration enables cooling of the mechanical resonator even in the unresolved sideband regime (USR). This study has some important guiding significance in the field of quantum information processing.

DOI
10.1088/1674-1056/adb266

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Abstract We theoretically investigate a cooling scheme assisted by a quantum well (QW) and coherent feedback within a hybrid optomechanical system. Although the exciton mode in the QW and the mechanical resonator (MR) are initially uncoupled, their interaction via the microcavity field leads to an indirect exciton-mode–mechanical-mode coupling. The coherent feedback loop is applied by feeding back a fraction of the output field of the cavity through a controllable beam splitter to the cavity’s input mirror. It is shown that the cooling capability is enhanced by effectively suppressing the Stokes process through coupling with the QW. Furthermore, the effect of the anti-Stokes process is enhanced through the application of the coherent feedback loop. This particular system configuration enables cooling of the mechanical resonator even in the unresolved sideband regime (USR). This study has some important guiding significance in the field of quantum information processing.
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Preparing macroscopic mechanical resonators close to their motional quantum groundstate and generating entanglement with light offers great opportunities in studying fundamental physics and in developing a new generation of quantum applications. Here we propose an experimentally interesting scheme, which is particularly well suited for systems in the sideband-unresolved regime, based on coherent feedback with linear, passive optical components to achieve groundstate cooling and photon-phonon entanglement generation with optomechanical devices. We find that, by introducing an additional passive element – either a narrow linewidth cavity or a mirror with a delay line – an optomechanical system in the deeply sideband-unresolved regime will exhibit dynamics similar to one that is sideband-resolved. With this new approach, the experimental realization of groundstate cooling and optomechanical entanglement is well within reach of current integrated state-of-the-art high-Q mechanical resonators.
We present a loop-shaping approach to coherent feedback (CF) control. By formulating the coupling between a quantum system and its environment in terms of the noise power spectrum, our method enables direct manipulation of the effective dissipation coefficients through spectral shaping. A systematic design framework for CF controllers is also developed, in which transfer functions are shaped to realize desired spectral responses. Applying this framework to optomechanical sideband cooling, we demonstrate that suppression of the Stokes process and enhancement of the anti-Stokes process can be simultaneously achieved, enabling ground-state cooling even in the unresolved-sideband regime. This loop-shaping framework provides an intuitive and general foundation for the design of CF controllers and can be extended to a wide class of quantum systems in which interactions with environments are characterized by noise power spectra.
Preparing macroscopic mechanical resonators close to their motional quantum groundstate and generating entanglement with light offers great opportunities in studying fundamental physics and in developing a new generation of quantum applications. Here we propose an experimentally interesting scheme, which is particularly well suited for systems in the sideband-unresolved regime, based on coherent feedback with linear, passive optical components to achieve groundstate cooling and photon-phonon entanglement generation with optomechanical devices. We find that, by introducing an additional passive element - either a narrow linewidth cavity or a mirror with a delay line - an optomechanical system in the deeply sideband-unresolved regime will exhibit dynamics similar to one that is sideband-resolved. With this new approach, the experimental realization of groundstate cooling and optomechanical entanglement is well within reach of current integrated state-of-the-art high-Q mechanical resonators.
Abstract Ground-state cooling of mesoscopic mechanical objects is still a major challenge in the unresolved-sideband regime. We present a frequency modulation (FM) scheme to achieve cooling of the mechanical resonator to its ground-state in a double-cavity optomechanical system containing a mechanical resonator. The mean phonon number is determined by numerically solving a set of differential equations derived from the quantum master equations. Due to efficient suppression of Stokes heating processes in the presence of FM, the ground-state cooling, indicated by numerical calculations, is significantly achievable, regardless of whether in the resolved-sideband regime or the unresolved-sideband regime. Furthermore, by choosing parameters reasonably, the improvement of the quantum cooling limit is found to be capable of being positively correlated with the modulation frequency. This method provides new insight into quantum manipulation and creates more possibilities for applications of quantum devices.