He Bing, Yang Liu, Lin Qing, Xiao Min
Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA.
College of Automation, Harbin Engineering University, Heilongjiang 150001, China.
Phys Rev Lett. 2017 Jun 9;118(23):233604. doi: 10.1103/PhysRevLett.118.233604.
One of the most fundamental problems in optomechanical cooling is how small the thermal phonon number of a mechanical oscillator can be achieved under the radiation pressure of a proper cavity field. Different from previous theoretical predictions, which were based on an optomechanical system's time-independent steady states, we treat such cooling as a dynamical process of driving the mechanical oscillator from its initial thermal state, due to its thermal equilibrium with the environment, to a stabilized quantum state of higher purity. We find that the stabilized thermal phonon number left in the end actually depends on how fast the cooling process could be. The cooling speed is decided by an effective optomechanical coupling intensity, which constitutes an essential parameter for cooling, in addition to the sideband resolution parameter that has been considered in other theoretical studies. The limiting thermal phonon number that any cooling process cannot surpass exhibits a discontinuous jump across a certain value of the parameter.
光机械冷却中最基本的问题之一是，在适当的腔场辐射压力下，机械振子的热声子数能达到多小。与以往基于光机械系统与时间无关的稳态的理论预测不同，我们将这种冷却视为一个动力学过程，即由于机械振子与环境处于热平衡状态，将其从初始热态驱动到纯度更高的稳定量子态。我们发现，最终留下的稳定热声子数实际上取决于冷却过程能有多快。冷却速度由有效光机械耦合强度决定，除了其他理论研究中考虑的边带分辨率参数外，该强度是冷却的一个关键参数。任何冷却过程都无法超越的极限热声子数在该参数的某一特定值处呈现出不连续的跳跃。
