实验研究铷原子蒸汽中脉冲真空压缩态的建立过程

发布时间：2019-05-22 07:29

【摘要】：压缩光科学的出现对整个物理学界有着重大影响,利用多种非线性光学过程产生的压缩光场及其性能优化是量子光学领域的研究热点。而在量子信息和量子精密测量领域,脉冲压缩光又有着十分广泛的应用,它的产生与噪声变化性质的研究为后续的连续变量量子通讯实验提供了前期准备。经过几十年的研究,产生脉冲压缩光场的方法有了很多种,其中包括:光学参量振荡、光力学、光与原子系综相互作用等。晶体中非线性光学转换的光谱带宽相当宽(约几个纳米量级),而像电磁诱导透明或拉曼共振这样的光与原子相互作用系统的带宽通常不超过MHz量级,所以与这些系统相互作用的压缩源需要在窄带宽频率处具有优异的噪声压制性能。除晶体压缩源的方案外,原子介质中的非线性光学过程同样可以产生非线性光场,例如非简并四波混频过程可以产生纳秒级脉冲宽度的双模压缩态和纠缠光场,而与之类似的一个非简并过程可以产生正交压缩真空场,研究者称其为光学偏振自旋转压缩,本文中的所有实验都是基于这种方案展开的,这种方法的最优噪声压缩达到了-3dB。当然关于偏振自旋转压缩的研究多数为连续光场的产生,对于脉冲压缩光场的产生、脉冲压缩态的建立过程、信号光场的噪声强度演化却鲜有涉及。基于这样的背景,我们重点研究了热铷87原子系综中,偏振自旋转效用产生的脉冲真空压缩态,并利用平衡零拍探测对压缩场的其正交分量进行采集,基于前人的研究,对正交分量做相位平均处理,测量了脉冲信号光的噪声强度随时间的演化,观测到信号光噪声从经典热态经历了微秒量级相互作用时间的急剧涨落,最后回落到真空压缩态的过程。
[Abstract]:The emergence of squeezed light science has a great influence on the whole field of physics. The squeezed light field produced by a variety of nonlinear optical processes and its performance optimization are the research hotspots in the field of quantum optics. In the field of quantum information and quantum precision measurement, pulse compressed light has a very wide range of applications. The study of its generation and noise changes provides a preliminary preparation for the subsequent quantum communication experiments with continuous variables. After decades of research, there are many methods to generate pulse squeezed light field, including optical parametric oscillations, photomechanics, interaction between light and atomic ensemble, and so on. The spectral bandwidth of nonlinear optical conversion in crystals is quite wide (about several nanometers), while the bandwidth of light-atom interaction systems such as electromagnetically induced transparency or Raman resonance usually does not exceed the order of MHz. Therefore, the compression sources interacting with these systems need to have excellent noise suppression performance at narrow bandwidth frequency. In addition to the scheme of crystal compression source, the nonlinear optical process in atomic medium can also produce nonlinear light field, such as the non-degenerate four-wave mixing process can produce two-mode squeezed state and entangled light field with nanosecond pulse width. A similar non-degeneracy process can produce orthogonal squeezed vacuum field, which researchers call optical polarization self-rotating compression. All the experiments in this paper are based on this scheme. The optimal noise compression of this method is-3dB. Of course, most of the research on polarization self-rotating compression is the generation of continuous light field. For the generation of pulse squeezed light field, the establishment process of pulse squeezed state, the evolution of noise intensity of signal light field is rarely involved. Based on this background, we focus on the pulse vacuum squeezed state produced by polarization self-rotation utility in thermal rubidium 87 atomic ensemble, and use balanced zero beat detection to collect the orthogonal components of the compression field, based on the previous research. The phase average processing of the orthogonal component is carried out, and the evolution of the noise intensity of the pulse signal light with time is measured. It is observed that the signal light noise has experienced a sharp fluctuation of the interaction time in the order of microseconds from the classical thermal state. Finally, the process of falling back to the vacuum squeezed state.
【学位授予单位】：华东师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O431.2

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