连续变量四组份纠缠态光场的产生

以一对工作在参量反放大状态的非简并光学参量放大器同时产生的两个正交振幅压缩相干态与两个正交位相压缩真空态光场为基础，经过不同位相关系的线性光学变换，可获得四组份纠缠态光场。我们将介绍实验原理和初步试验结果。     

双模光场压缩态的实验研究

利用非简并参量下转换过程,在实验上获得了双模光场压缩态,在电磁场的一正交位相分量上噪声水平较真空噪声水平下降近30％。     

利用正交压缩态光场实现连续变量的量子密码术

文中提出一种利用单模正交压缩态光场作为密码载体的连续变量量子密钥传输方案，在该方案中，经典信号以二进制编码形式调制在单模正交压缩态光的正交振幅分量或正交位相分量上，基于海森保测不准关系，任何窃听都会导致合法通讯者之间的误码率升高，从而暴露了窃年者的存在，以保护密钥信息的安全，与采用同样方案的相干光相比，保密程度有较大的提高。     

连续变量纠缠态光场在光纤中传输特性的实验研究

连续变量纠缠态由于其确定性产生、高效率的特点而被广泛应用于连续变量量子信息处理.在量子信息处理过程中纠缠态与量子信道发生相互作用而退相干,这是限制长距离量子信息发展的重要因素之一.光纤信道作为理想的量子信道,是目前连续变量量子信息研究关注的热点.本文利用Ⅱ类匹配的楔角极化磷酸氧钛钾晶体构成了三共振的非简并光学参量放大器,获得了8.3 dB的光通信波段1.5μm连续变量纠缠态光场.将产生的纠缠态光场注入单模光纤,其量子特性在传输距离达50 km后仍得到保持,纠缠度为0.21dB.该研究可为基于光纤的长距离连续变量量子信息研究提供有效的依据.     

压缩态光场的四阶量子干涉

采用半经典理论讨论了同一抽运源抽运的两个独立光学参量振荡腔(OPO)所产生的压缩态光场的四阶量子干涉效应．结果表明：在OPO振荡阈值处,输出光场压缩度最高但四阶量子干涉最弱,条纹可见度为33.3%,远离阈值时干涉越来越强. 关键词：     

偶数模四态叠加多模叠加态光场的高次差压缩

构造了由偶数模多模复共轭奇相干态与多模复共轭偶相干态线性叠加所组成的第Ⅱ种偶数模四态叠加多叠模加态光场|Ψ_oe⁽⁴⁾,Ⅱ>_2q.利用多模压缩态理论,研究了态|Ψ_oe⁽⁴⁾,Ⅱ>_2q的等幂次高次差压缩特性.结果发现:在一定条件下,态|Ψ_oe⁽⁴⁾,Ⅱ>_2q的两个正交相位分量可同时呈现出广义非线性等幂次高次差压缩效应.     

宽频带压缩态光场光学参量腔的设计

压缩态光场是量子光学研究中的一种重要量子资源.在量子信息应用中,压缩态光场的频谱带宽是限制信息传输容量的重要指标.目前,光学参量振荡器是产生强压缩度非经典光场最有效的方法之一.本文通过分析输出耦合镜透射率、线宽、阈值功率对简并光学参量振荡器频谱带宽的影响,实验完成了低阈值(18 mW)、宽频带(84.2 MHz)、高稳定(锁定基线标准偏差为0.32 MHz)量子压缩器的设计.结果表明,相比单共振光学参量振荡器,双共振腔型具有低阈值、高稳定的特点,更适合于宽频带压缩态光场的制备与实际应用.     

多模叠加态光场的不等阶Nj次H压缩

非对称多模叠加态光场|Ψ(ab)>q= C(aI)pq|{iZ(a)*j}.>q+C(bI)nq|{-iZ(b)* j}.>q, 利用多模辐射场的不等阶压缩一般理论,首次对态|Ψ(ab)>q 的广义非线性不等阶Nj次方H压缩特性进行了详细地研究,结果表明在不同的条件下, 态|Ψ(ab)>q的两个正交分量分别呈现周期性变化的、任意不等阶Nj次方H压缩效应、Nj-H最小测不准态,说明态|Ψ(ab)>q是一种典型的非经典多模光场.     

连续变量1.34 μm量子纠缠态光场的实验制备

设计研制了连续单频671 nm/1342 nm双波长激光器,并通过模式清洁器降低了激光器额外噪声.利用该低噪声连续单频激光器抽运由Ⅱ类准相位匹配晶体构成的双共振非简并光学参量放大器,实验制备出纠缠度达3 dB的光通信波段1.34μm连续变量量子纠缠态光场.该波段量子纠缠态光场在光纤中传输损耗低且相散效应小,与现有的光纤通信系统相兼容,可用于实现基于光纤的实用化连续变量量子通信.     

第Ⅲ类三态叠加多模叠加态光场的广义非线性Nj次方H压缩

根据量子力学中态的线性叠加原理,构造了由多模复共轭相干态|{zj{iZj*}>q及多模真空态|{0j}>q线性叠加所组成的第Ⅲ类三态叠加多模叠加态光场|ψ3(3)>q.利用多模压缩态理论,研究了态的广义非线性不等幂次Nj次方H压缩效应.结果表明,仅当各模的压缩次数之和为偶数时,各模初始位相ψj(j=1,2,…,q)与各模压缩次数Nj的乘积Njψj之和及态|ψ3(3)>q中任意两态间初始位相差(θi-θj)(i,j=1,2,3)满足一定的条件下,态|ψ3(3)>q的第一和第二正交相位分量分别可呈现周期性变化的、任意次的广义非线性不等幂次Nj次方H压缩效应.     

Squeezing Properties of the Generalized Multimode Squeezed States

By means of the invariance of Weyl ordering under similar transformations we derive the explicit form of the generalized multimode squeezed states.Moreover,the completeness relation and the squeezing properties of the generalized multimode squeezed states are discussed.     

Continuous Variable Remote State Preparation with a Two-Mode Squeezed Vacuum State

Continuous variable remote state preparation is presented using a two-mode squeezed vacuum state based on the Heisenberg representation. We show that it is possible to remotely prepare this state in principle. Our scheme’s main advantages are: (i) It is practical, because a two-mode squeezed vacuum state is easy achieved in experiment, and our scheme only requires a beam splitter and a feedforward; (ii) Using our scheme decoherence and being cheating can be avoided.     

Three-Party Quantum Key Agreement Protocol Based on Continuous Variable Single-Mode Squeezed States

The difficulty of quantum key agreement is to realize its security and fairness at the same time.This paper presents a new three-party quantum key agreement protocol based on continuous variable single-mode squeezed state.The three parties participating in the agreement are peer entities,making same contributions to the final key.Any one or two participants of the agreement cannot determine the shared key separately.The security analysis shows that the proposed protocol can resist both external and internal attacks.     

Teleportation of Squeezed Entangled State

Based on the coherent entangled state ｜a, x〉 we introduce the squeezed entangled state （SES）. Then we propose a teleportation protocol for the SES by using Einstein-Podolsky-Rosen entangled state ｜η〉 as a quantum channel. The calculation is greatly simplified by virtue of the Schmidt decompositions of both ｜a, x〉 and ｜η〉. Any bipartite states that can be expanded in terms of ｜a, x〉 may be teleported in this way due to the completeness of ｜a, x〉.     

两态叠加多模叠加态光场的二阶不等幂次高次差压缩效应(英文)

利用多模辐射场(简称MRLF)广义非线性不等幂次高次差压缩的一般理论,研究了由2q模相干态与其相反态线性叠加构成的两态叠加多模叠加态光场|ψ1(2)〉2q的二阶不等幂次高次差压缩(即Nj次幂x压缩)特性。结果发现:该多模叠加态光场在某些条件下呈现Nj次方x压缩效应。     

时域多模飞秒压缩光场测量中的本地光脉冲整形研究

基于飞秒脉冲的同步泵浦参量过程产生的多模时域飞秒压缩光场,由于其独特的优势,特别是可以享有单模光纤网络兼容,是实现可扩展量子计算及大容量量子通讯的良好光源。由于无法实现多模时域飞秒压缩光场的空间分离,目前对于多模时域飞秒压缩光场的测量,采用最为有效的平衡零拍探测。因此如何构造与时域飞秒压缩光场时域函数分布相同的本地光,是其中的关键内容,并直接影响测量效果。本文主要理论研究了本地脉冲光的时域整形方案,分析了系统参数对整形后的多模本地光的保真度以及系统调制效率的影响,并结合实验参数提出可能的解决办法。     

Continuous variable entanglement generation in coupled cavities

We investigate continuous variable entanglement produced in two distant coupled cavities, in which two four-level atoms are driven by classical fields respectively. Under the large detuning condition, an effective Hamiltonian containing the square of the creation (annihilation) operator of the cavity field is derived. Due to the nonlinearity, entanglement formally created by the beam splitter type interaction is transformed into the nondegenerate parametric down conversion type. Employing the operator algebraic method, we study the time evolution of the entanglement condition, and show that the system provides us an advantage in achieving a larger photon number with better entanglement. We also discuss the dissipation of the cavities affecting the entanglement.     

Casimir Force of Squeezed Vacuum

The Casimir force of the quantized electromagnetic field in the squeezed vacuum state is calculated betweena pair of parallel perfectly conducting plates at zero temperature.     

Casimir Force of Squeezed Vacuum

The Casimir force of the quantized electromagnetic field in the squeezed vacuum state is calculated between a pair of parallel perfectly conducting plates at zero temperature.