微纳米机械振子中二次耦合问题的理论研究

Under quantum limit measurement, entanglement and photon blockade in micro system, such as system including photons and atoms, inevitably cause quantum demolition measurement. Thus, how to explore quantum phenomena in macroscopic system has very important practical significance. Entanglement and photon blockade produced in macroscopic system, such as mechanical oscillator system, have become one of the attractive research fields. However, almost all the system consisted by mechanical oscillator is linear coupling. From the experimental point of view, this linear coupling system has two challenges: one chanllenge is integrating sensitive micromechanical elements into high finesse cavities without compromising the mechanical or optical properties of either；Another challenge is to read out the mechanical element's quantum state. To solve these problems mentioned above, the present research focous on: (1) How to generate entanglement in quadratic coupling system of mechanical oscillator, as well as enhance entanglement degree with mechanical oscillator system which couples with atoms; (2) We will study photon blockade effect in quadratic coupling system of mechanical oscillator, and prove the stonger photon blockade effect can be produced in this system. Moreover, we will analyze the affecting of the parameters, such as environment temperature, classical field and the noise on photon blockade. The present study will provide theoretical support on how to correctly readout quantum state of quantum entanglement and photon blocking effect.

微观系统产生的纠缠和光子阻塞效应，如光子和原子等系统受到量子极限测量的限制而不可避免地引起量子破坏性测量。因而，探究宏观系统的量子现象具有非常重要的实际意义。利用机械振子这种宏观系统产生的纠缠和光子阻塞效应是目前研究的热点之一。然而，这种机械振子系统有一个共同点就是光学腔模与力学振子的坐标的耦合是线性的。从实验的角度来看，这种线性耦合系统中，一方面微纳米振子与高精度腔耦合会影响到力学或光学特性；另一方面不能正确读出力学振子的量子态。为解决以上问题，本项目计划研究:（1）利用机械振子中的二次光力耦合产生连续变量纠缠以及振子系统与原子相结合提高连续变量纠缠度；（2）研究机械振子中的二次光力耦合系统中的光子阻塞效应，证明机械振子系统能够产生较强的光子阻塞效应，分析环境温度、经典场的强度以及噪音对光子阻塞效应的影响。本项目的研究为正确读出纠缠和光子阻塞效应的力学振子的量子态提供理论支持。

研究宏观二次耦合光力系统中的连续变量纠缠具有重要的科学意义：一方面二次耦合系统能正确读出力学振子的量子态并且可以精确地测量其位置、压力和动量；另一方面，连续变量纠缠在量子通信中具有比特速率高等潜在优越性，同时其有无穷多自由度而比单个比特具有更大存储能力。我们研究了:（1）提出在二次光力耦合与原子相结合产生并提高连续变量纠缠的方法；（2）提出机械振子系统产生四体连续变量纠缠的方案，证明其能够产生真正的多体连续变量纠缠，分析了这种多体纠缠在量子密钥分配中的应用。