基于非相干碰撞和自发辐射实现纠缠调控及增强的理论与实验研究

In contrast to the general thought that collision and spontaneous emission are dephasing in nature and detrimental to the generation of entanglement, in this project, we theoretically and experimentally investigate the effect of incoherent collision and spontaneous emission on entanglement between the produced four-wave-mixing field and signal field in atomic or melecular multi-level systems driven by the signal and strong pump fields, and demonstrate that the manipulation of light-light entanglement can be realized via collision- and spontaneous-decay-incuced quantum coherence and interference and the degree of entanglement can be enhanced dramatically under certain conditions. Considering the 3S-3P1/2,3/2-5S(or 4D) rhomb-type Na atomic system, 5S(F=2,F=3)-5P1/2,3/2-5D3/2 double-rhomb-type 85Rb atomic system, and Y-type sodium molecular system, we experimentally examine the entanglement property of the four-wave-mixing field and signal field with the balanced homodyne detection system by varying the experimental conditions, such as the sample temperature, buffer gas pressure, intensity or frequency detuning of the laser fields; moreover, we present a theoretical analysis and explanation by solving the Heisenberg-Langevin equations. This project provides a new and efficient way to further investigation on the generation and manipulation of entanglemen in realistic atomic or molecular system, and may find potential application in quantum computation, quantum communications, and quantum network.

与通常人们所认为的消相干碰撞和自发辐射总不利于纠缠制备的观点不同，本课题从理论和实验上研究碰撞和自发辐射对原子分子多能级系统在信号场和强泵浦场作用下产生的四波混频场与信号场间纠缠的影响，论证利用这两种非相干过程所产生的量子相干和干涉可实现光场-光场间纠缠的调控,且在一定条件下能够显著地增强纠缠。实验上选取钠原子3S-3P1/2,3/2-5S(或4D) 菱型、Rb85原子5S(F=2,F=3)-5P1/2,3/2-5D3/2双菱型和钠分子Y型多能级系统，利用平衡零拍探测系统来检测不同实验条件下(如样品池温度、缓冲气体气压及激光场强度或频率失谐等)四波混频场与信号场间纠缠特性，同时通过求解海森堡-郎之万方程进行理论分析和解释。该课题为进一步研究实际原子分子系统中纠缠的制备及控制提供了一种新的有效方案，可望在量子计算、量子通信及量子网络等方面具有潜在的应用前景。

如何方便高效地实现多体纠缠的产生、分发、存储、再现及调控，是量子信息推广到实际应用进程中需要解决的最基本最核心问题。本课题主要对原子及原子-腔光力混合系统中压缩态和多体纠缠态的制备及调控进行研究。提出了一种在Λ型三能级原子系综中利用强耦合场和探测场产生的原子相干来实现原子自旋压缩的制备和调控方案；考虑在单入射光场驱动单腔光机械系统中，当腔场的自由频谱宽度与机械振子频率相比拟时，论证利用基于光场辐射压产生的腔场与动镜间的耦合可实现三体纠缠；考虑在单腔光机械系统引入Λ型三能级原子，论证利用原子相干可显著增强光场-腔镜-光场三体纠缠，且可实现光场-光场-腔镜-原子间四体纠缠；考虑传统的Λ型三能级原子系统及单腔光机械系统在强泵浦场和相对较弱探测场作用下，计及强泵浦场和探测场的量子特性，提出了两种新的量子效应—电磁诱导原子自旋压缩和腔光力诱导纠缠。该课题为只利用相干光场实现非简并、窄带宽连续变量多光场纠缠、光场-原子-腔镜间多体纠缠的制备及调控提供了一种简便有效的方法，可望在高精度原子物理测量、量子相干控制、量子计算、可扩展量子通信及量子网络等方面具有潜在的应用前景。