Continuous-variable quantum teleportation of even and odd coherent states through varied gain channels

This paper has investigated quantum teleportation of even and odd coherent states in terms of the EPR entanglement states for continuous variables. It discusses the relationship between the fidelity and the entanglement of EPR states, which is characterized by the degree of squeezing and the gain of classical channels. It shows that the quality of teleporting quantum states also depends on the characteristics of the states themselves. The properties of teleporting even and odd coherent states at different intensities are investigated. The difference of teleporting two such kinds of quantum states are analysed based on the quantum distance function.     

基于高阶厄米高斯模倾角测量

本文主要对高阶厄米高斯模式的倾角测量进行了理论分析,提出了利用高阶厄米高斯模式可以进一步提高倾角测量的方案,并对不同模式进行倾角测量的精度进行了对比。计算结果表明,采用的模式的阶数越高,倾角测量的精度越高,这一结果为进一步提高倾角测量实验提供理论依据。     

Generation of squeezed TEMM01 modes with periodically poled KTiOPO4 crystal

Spatial quantum optics and quantum information based on the high order transverse mode are of importance for the super-resolution measurement beyond the quantum noise level. We demonstrated experimentally the transverse plane TEM₀₁ Hermite-Gauss quantum squeezing. The squeezed TEM₀₁ mode is generated in a degenerate optical parametric amplifier with the nonlinear crystal of periodically poled KTiOPO₄. The level of 2.2-dB squeezing is measured using a spatial balance homodyne detection system.     

Experimental Demonstration of a Displacement Measurement of an Optical Beam beyond the Quantum Noise Limit

We experimentally generate a spatially squeezed light beam and realize a small-displacement measurement beyond the quantum noise limit with this squeezed light. Moreover, we measure about -2.2±0.2dB spatial squeezing and reduce the minimum measurable displacement from 1.17A to 0.99A with the signal-to-noise ratio normalized to 1.     

确定性量子分束器的实验研究

基于"时间反演"的HOM干涉原理,利用一个普通的分束器将Ⅰ类自发参量下转换过程产生的一对飞秒脉冲量级、简并单光子对完全分离,分束效率最高可以达到92%。     

通过λ/2波片外腔同位相弱反馈实现激光二极管激光的强度噪声压缩

由于低温下单模半导体量子阱激光器与准直透镜出现双折射效应,导致输出光场偏振状态发生变化,使单个线偏模的光子数噪声增加.利用λ/4波片补偿双折射,同时采用λ/2波片前后表面的同位相余反射光完成对激光二极管激光器的弱反馈,在抽运电流为34.65mA时,获得压缩度为2.8dB,输出功率约24mW的光子数压缩光 关键词： 噪声压缩 弱反馈 反关联     

EIT增强色散及光速减慢的实验研究进展

EIT(Electromagnetic induced transparency)导致的光速减慢(Slow light)、光信号存储等现象使人们有可能驾驭自然界最迅速而又难以捉摸的能量形式,为量子信息的存储与提取带来了方便,因而在量子信息处理中有极大的应用潜力,对于量子信息和量子计算的发展具有重要意义. 我们在国家海外杰出青年基金(69928504),国家自然科学基金(69978013)以及山西省青年科学基金(20001016)的支持下开展了Cs原子的EIT实验及理论研究.在常温Cs原子汽室中探测到由原子相干布居导致的60%电磁感应透明凹陷以及在透明凹陷区较大的色散增强现象,通过色散曲线推测到探针光在Cs原子汽室中光速减慢了1/418倍. 实验中我们使用两台带宽小于2MHz的可调谐外腔反馈半导体激光器作为探针光和泵浦光,分别将其调谐于铯原子D2线的超精细能级跃迁(62S1/2,F=3→62S3/2,F′=4)线附近和锁定于共振跃迁(62S1/2,F=4→62S3/2,F′=4)线上,并使探针光与泵浦光同向传输经过Cs原子汽室消除多普勒效应的影响.探针光和泵浦光功率分别为4.7μW和264μW.实验结果表明,由于EIT效应,使探针光在Cs原子汽室中的传输速度得到较大的减慢.由探针光在原子汽室中的色散曲线斜率得到在共振频率处Cs原子的折射率系数变化为δn/δω=1.89×10-13Hz-1,从而得知光在原子汽室中群速度的降低值. 与此同时,我们也观察到在非共振区Cs原子吸收增强效应.这一效应导致原子出现反常色散现象,预示着光在原子汽室中速度有所增加.目前我们正在通过对探针光进行强度调制来完成光速减慢以及增快的直接测量.     

强耦合条件下内腔电磁诱导透明和正交模劈裂的研究

文章分析了Λ-型三能级原子与腔耦合系统在强耦合条件下,腔透射谱在随腔模失谐的变化情况。结果表明,改变腔模失谐不但对正交劈裂峰会产生频移,同时对内腔EIT峰也会产生频率推移,并且在单光子失谐时,推移程度也有所不同;当腔模失谐达到自由光谱区的一半时,内腔暗态极子模出现双峰结构。这一结果对研究基于原子腔系统的关联光场具有积极的意义。     

Approximation Analytical Solution for a Current-Carrying Ion Sheath and its Chaos Control

The fourth-order quantum interference of squeezed fields generated by two independent optical parametric oscillators(OPOs) is discussed based on the semi-classical theory. It is shown that at the oscillation threshold of OPOs the squeezing of two output fields is the highest but the fringe visibility of fourth-order interference is the lowest(33.3%). When the pump power is away from the threshold, the squeezing decreases while the correlation between them increases.     

Fidelity of Quantum Teleportation for Single-Mode Squeezed State Light

The fidelity of quantum teleportation of a single-mode squeezed state of light is calculated based on the general theory of quantum-mechanical measurement in the Schrodinger picture. It is shown that the criterion for the nonclassical state teleportation is different from that for coherent state. F = 1/2 is no longer the rigorous boundary between classical and quantum teleportation for a squeezed state of light. When the quantum entanglement of an Einstein-Podolsky-Rosen （EPR） beam used for teleportation and the parameters of the system are given, the fidelity depends on the squeezing of the input squeezed state. The higher the squeezing is, the smaller the fidelity is, and the lower the classical limitation of fidelity is. The dependence of the optimum gain for teleporting a squeezed vacuum state upon the EPR entanglement is also calculated. The results obtained provide important references for designing experimental systems of teleporting a non-classical state and judging the quality of the teleported quantum state.