Theoretical Research On Ground-state Cooling Of The Mechanical Resonator In Double-cavity Optomechanical System

Cavity optomechanics is a cutting-edge subject integrating quantum optics and mechanical science,which mainly studies the interaction between cavity(microwave)field and mechanical motion object.The cavity optomechanical system has received extensive attention in both basic research and practical applications and has important application values in the fields of biological sensing,weak classical force detection and quantum information processing.In recent years,the preparation of the cavity optomechanical system has also been continuously optimized benefited from the rapid development of micro-nano manufacturing.Therefore,the cavity optomechanical system has increasingly become an ideal platform for studying macroscopic quantum effects and realizing effective quantum manipulation.It is well known that mechanical resonators are easily excited in a thermal environment,so cooling successfully close to their quantum ground-state is an important prerequisite for the observation of quantum behavior.However,most of the conventional ground-state cooling schemes satisfy the resolved sideband condition,which require the system to be in a sideband condition where the frequency of the mechanical mode is much larger than the dissipation rate of the cavity mode.At the same time,the cooling limit of the mechanical resonators is greatly limited by the non-negligible effects of swap heating and quantum backaction heating during the system cooling process in the case of strong optomechanical coupling region.Based on the above considerations,this paper propose two ground-state cooling approaches to improve the cooling effect focused on the unresolved-sideband region and the strong coupling region.Firstly,a scheme to improve the cooling effect of the mechanical resonator with frequency modulation based on the double-cavity optomechanical system is proposed.Two cavity modes couple to the same mechanical mode via the radiation pressure,which forms two cooling channels to increase the energy exchange paths between phonons and photons.The Stokes heating process can be completely suppressed by synchronously modulating the frequencies of the cavity modes and the mechanical resonator,successfully reducing the mean phonon number below the quantum reaction limit without frequency modulation.And with the help of periodic frequency modulation,a more ideal cooling effect of the mechanical resonator not only obtains in the weak coupling region and strong coupling region,but also the successful realization of cooling in the system unstable region.It is demonstrated by numerical simulations that the mechanical resonator can achieve ideal cooling performance even in the unresolved-sideband region.And reasonable adjustment of system parameters can effectively improve cooling efficiency.This scheme is of great significance for the quantum manipulation of a large-scale mechanical object.Secondly,a scheme to optimize the cooling performance by exploiting the cavity modes dissipations in the strong coupling region is proposed,which considers a double-cavity optomechanical system with two coupled-cavity modes.Cavity dissipations are used as a kind of tunable resource in this scheme.By periodically introducing the high cavity mode dissipations,the swap heating effects and quantum backaction heating are effectively suppressed.Therefore,the cooling rate is significantly improved and the cooling limit is also greatly reduced.In addition,we also discuss the self-regulating properties of dynamic dissipation modulation and the cooling rate can be adjusted at any time.This scheme provides a mew path to perform long-coherent quantum operations in the strong coupling region.