精确求解级联型三能级原子与单模相干态光场场熵的演化特性

本文利用全量子理论,在非旋波近似下对单模相干态光场与级联型三能级原子相互作用过程中场熵随时间的演化进行了精确求解.数值计算的结果表明：随着初始时刻平均光子数n以及光场与原子的耦合强度u, v的增大,场熵的平均值先增大后减小,因此纠缠度也同样先增大后减小;随着失谐量Δ的增大,场熵的平均值逐渐减小,因此纠缠度也逐渐减小. 关键词： 相干态正交化展开 非旋波近似 场熵     

Kerr效应和虚光场对三能级原子-场系统光子反聚束效应的影响

研究Kerr介质中,非旋波近似下,一个级联型三能级原子与光场相互作用的二阶相干度的时间演化,讨论了Kerr效应和虚光场效应对场的光子反聚束效应的影响.结果表明,虚光场的影响使系统出现量子噪声;而Kerr介质常量x、共振频率ω的增大及原子-场耦合系数g的减小都将降低原子对激发场的吸收效率,削弱受激辐射场的光子反聚束效应,其中以g的变化对系统的影响最为明显. 关键词： 非旋波近似 Kerr效应 反聚束     

T-C模型中虚光子过程对光场压缩效应的影响

利用全量子理论,研究非旋波近似下TC模型中受激场的压缩效应.结果表明:非旋波近似下,由于虚光场的影响,Q的演化曲线出现了“小锯齿状”,表现为系统的量子噪声,随着ω和n的增大,量子噪声分别减小和增大,虚光子过程使光场的压缩程度明显加深;研究结果还揭示了原子场耦合系数λ及原子间耦合系数g与光场压缩效应的关系. 关键词： T-C模型 非旋波近似 压缩效应 量子噪声     

非旋波近似下两个二能级原子与单模光场相互作用的非经典性质

利用全量子理论,研究了非旋波近似下两个二能级原子与单模光场相互作用过程中光场所表现出的非经典性质,揭示了虚光子过程对场的平均光子数和二阶相干度的影响,并讨论了光场频率及原子间耦合系数的变化与场的平均光子数和二阶相干度的关系.     

虚光场对双模压缩真空场与原子相互作用系统中光子统计性质的影响

研究了非旋波近似下双模压缩真空场与二能级原子相互作用系统中光子的统计性质,着重讨论了虚光场效应对光子统计性质的影响.数值计算结果表明,虚光场对光子统计性质的影响主要表现为量子噪声,量子噪声的大小依赖于光场的初始压缩因子和原子的初始状态,且与原子光场耦合强度有关. 关键词： 非旋波近似 双模压缩真空场 二能级原子 光子统计性质     

囚禁离子与单模场的相互作用

研究了囚禁离子与单模量子辐射场构成的相互作用系统在载波激发(ωL=ω0)、红激发［ωＬ=ω0-jν(j=1,2,3)］和蓝激发［ωL=ω0+jν(j=1,2,3)］情形下的统计性质.讨论了系统的态函数随时间的演化关系、光子态和声子态交换的条件及相应的离子布居数，得到了光子数和声子数的平均值及其方差、光子场和声子场的二阶相干度等量值. 关键词： 囚禁离子 单模量子辐射场 声子场 旋波近似     

与双模场依赖强度耦合下多光子通道中原子比特周期量子回声产生和调控

旋波近似条件下,运用全量子理论研究了与双模相干光场依赖强度耦合多光子通道中原子比特周期量子回声的产生和控制,采用数值计算的方法,讨论了双模相干光场平均光子数分布形式、分布范围及原子跃迁时吸收(或发射)的光子数k对原子比特态保真度演化的影响,获得了产生和控制原子比特周期量子回声的系统参量；根据纠缠理论,分析了原子比特态保...     

非旋波近似下Λ型三能级原子与相干态光场的量子纠缠

在非旋波近似下,利用相干态正交化展开方法,对相干态光场与Λ型三能级原子相互作用的量子场熵进行了精确求解.利用量子熵理论讨论了耦合强度、平均光子数以及初始时刻原子处于不同的能级对量子纠缠的影响.数值计算的结果表明：当初始时刻原子处于激发态时,量子纠缠在较短的时间内就能演化到最大值,随着平均光子数的增大,纠缠演化的周期性逐渐明显|原子初始时刻处于三个能级的叠加态会使初始阶段量子纠缠显著降低|与旋波近似下的结果不同的是,随着耦合强度以及平均光子数的增加,非旋波项的贡献显著增强,使得量子纠缠演化曲线出现小锯齿状的振荡.     

双模场与原子相互作用中的量子纠缠和内禀退相干

通过求解系统的Milburn方程，研究了两能级原子与双模SU(1,1)相干态光场发生相互作用系统中，原子与场的纠缠及双模SU(1,1)相干态场的模间纠缠随时间的演化问题，讨论了内禀退相干、双模光子数差等对纠缠度的影响.结果表明，存在内禀退相干时，随着时间的演化，场-原子纠缠逐渐减小到一个确定值，而模间纠缠逐渐增大到一个确定值，两者演化的最终值只取决于双模光子数差和平均光子数，而与内禀退相干因子无关. 关键词： Milburn理论 SU(1 1)相干态 量子约化熵 量子相对熵     

非旋波近似下Λ型三能级原子与相干态光场的量子纠缠

在非旋波近似下,利用相干态正交化展开方法,对相干态光场与Λ型三能级原子相互作用的量子场熵进行了精确求解.利用量子熵理论讨论了耦合强度、平均光子数以及初始时刻原子处于不同的能级对量子纠缠的影响.数值计算的结果表明:当初始时刻原子处于激发态时,量子纠缠在较短的时间内就能演化到最大值,随着平均光子数的增大,纠缠演化的周期性逐渐明显;原子初始时刻处于三个能级的叠加态会使初始阶段量子纠缠显著降低;与旋波近似下的结果不同的是,随着耦合强度以及平均光子数的增加,非旋波项的贡献显著增强,使得量子纠缠演化曲线出现小锯齿状的振荡.     

Kerr 介质中三能级原子与双模场非共振相互作用的量子统计性质

研究了Kerr介质中双模场与V型三能级原子的非共振相互作用. 对Cauchy-Schwartz不等式的研究表明,在两模场失谐量相等(δ₁=δ₂)条件下,当初始场强ξ一定而两模场的光子数差q减小时,场的非经典相关程度加强;q一定而ξ增大时,场的非经典相关程度减弱. 当Δδ=|δ₂-δ₁|≠0且q和ξ的取值一定时,随介质常量x的增大,光场两模间的非经典相关程度减弱,且Δδ的大小对这种非经典相关程度的减弱有重要影响. 对场的 关键词： Kerr介质 非共振相互作用 Cauchy-Schwartz不等式 场的二阶关联函数     

非对称自旋-轨道耦合系统的多体量子相干含时演化

本文以具有非对称性自旋相互作用的三体自旋系统为研究对象,重点研究了三体量子相干含时演化规律.采用精确量子对角化和基于量子主方程的数值模拟方法,讨论了三体量子系统中多种量子相干组分及其退相干.研究发现,量子相干组分的含时演化与整个系统的初态量子特性紧密相关.当初态为可分离纯态时,在较短时间内,非对称相互作用有利于增加多体量子相干度.这些量子相干度因受噪声影响而逐渐衰减.当初态为类Werner态时,量子相干度的分布满足加和性,即三体量子相干度等于所有两体量子相干度之和.自旋之间非对称相互作用和环境噪声都会引起三体量子相干度大于所有两体量子相干度之和.这些结论有助于多体量子资源的制备.     

初态对光波导阵列中连续量子行走影响的研究

本文使用近邻耦合模型得到的解析解,分析了周期性波导中输入态对量子行走的粒子数的概率分布函数 和二阶相干性的影响.结果表明:输入态的对称性质对量子行走过程的二阶相干度有影响, 而对粒子数的概率分布函数影响不大. 关键词： 周期性光波导阵列 量子行走 二阶相干度 纠缠态     

三能级电磁感应透明中辐射场的量子统计特性

对Λ型三能级原子电磁感应透明（EIT）过程中辐射场的二阶相干度进行了研究。理论分析表明，在电磁感应透明系统中，由于原子的相干效应导致其上能级共振荧光场的二阶相干度将呈现单光子场的量子统计特性。并对其随耦合场强度和探测光失谐的变化进行了详细的分析和讨论，结果发现：在｜Ω｜〉（Γ2＋Γ3）／2情况下．采用较弱的耦合光功率（由托比频率Ω表征）及较大的探测光失谐，在较长时间延迟范围内，二阶相十度保持小于1，更利于实现非经典场的量子统计行为；相反，在｜Ω｜≤（Γ2＋Γ3）／2情况下，探测光的失谐量越小，越利于获得二阶相干度小于1的量子统计光场。南此可见选取合适的参量可优化电磁感应透明过程中单光子场的量子统计特性。     

Protecting quantum coherence of two-level atoms from vacuum fluctuations of electromagnetic field

In the framework of open quantum systems, we study the dynamics of a static polarizable two-level atom interacting with a bath of fluctuating vacuum electromagnetic field and explore under which conditions the coherence of the open quantum system is unaffected by the environment. For both a single-qubit and two-qubit systems, we find that the quantum coherence cannot be protected from noise when the atom interacts with a non-boundary electromagnetic field. However, with the presence of a boundary, the dynamical conditions for the insusceptible of quantum coherence are fulfilled only when the atom is close to the boundary and is transversely polarizable. Otherwise, the quantum coherence can only be protected in some degree in other polarizable direction.     

Coherence theory and coherence phenomena in a closed spin‐1/2 system

A simplified Heisenberg spin model is studied in order to examine the idea of decoherence in closed quantum systems. For this purpose, we present a quantifiable definition to quantum coherence Ξ, and discuss in some detail a general coherence theory and its elementary results. As expected, decoherence is understood as a statistical process that is caused by the dynamics of the system, similar to the growth of entropy. It appears that coherence is an important measure that helps to understand quantum properties of a system, e.g., the decoherence time can be derived from the coherence function Ξ(t), but not from the entropy dynamics. Moreover, the concept of decoherence time is applicable in closed and finite systems. However, in most cases, the decay of off‐diagonal elements differs from the usual exp(‐t/τ_d) behaviour. For concreteness, we report the form of decoherence time τ_d in a finite Heisenberg model with respect to the number of particles N, density n_ρ, spatial dimension D and ? in a η/r^?‐type of potential.     

Two-photon correlations of luminescence at the Bose-Einstein condensation of dipolar excitons

Correlations of the luminescence intensity (the second-order correlation function g ⁽²⁾(τ)), where τ is the delay time between the photons detected in pairs) under the conditions of the Bose-Einstein condensation (BEC) of dipolar excitons has been studied in a temperature range of 0.45–4.2 K. Photoexcited dipolar excitons have been accumulated in a lateral trap in a GaAs/AlGaAs Schottky diode with a 25-nm wide single quantum well with an electric bias applied across the heterolayers. Two-photon correlations have been measured with the use of a two-beam intensity interferometer with a time resolution of }~0.4 ns according to the well-known classical Hanbury-Brown-Twiss scheme. The photon bunching has been observed at the onset of Bose-Einstein condensation manifested by the appearance of a narrow exciton condensate line in the luminescence spectrum at an increase in the optical pumping (the line width near the threshold is ?200 μeV). At the same time, the two-photon correlation function itself obeys the super-Poisson distribution, g ⁽²⁾(τ) > 1, at time scale τ_c ? 1 ns of the system coherence. The photon bunching is absent at a pumping level substantially below the condensation threshold. The effect of bunching also decreases at pumping significantly above the threshold, when the narrow exciton condensate line starts to dominate in the luminescence spectra, and finally disappears with the further increase in the optical excitation. In this region, the distribution of pair photon correlations is a Poisson distribution manifesting the united quantum coherent state of the exciton condensate. Under the same conditions, the first-order spatial correlation function g ⁽¹⁾(r) determined from the interference pattern of the luminescence signals from the spatially separated parts of the condensate at constant pumping remains noticeable at distances of no less than 4 μm. The discovered effect of photon bunching is very sensitive to temperature and decreases by several times with a temperature increase in the range of 0.45–4.2 K. Assuming that the luminescence of the dipolar excitons directly reflects the coherence properties of the gas of interacting excitons, the discovered photon bunching at the onset of condensation, where the fluctuations of the exciton density and, consequently, of the luminescence intensity are most significant, indicates a phase transition in the interacting Bose gas of excitons, which is an independent way of detecting the Bose-Einstein condensation of excitons.     

Spatial coherence of polaritons in a 1D channel

We analyze time evolution of spatial coherence of a polariton ensemble in a quantum wire (1D channel) under constant uniform resonant pumping. Using the theoretical approach based on the Lindblad equation for a one-particle density matrix, which takes into account the polariton-phonon and excitonexciton interactions, we study the behavior of the first-order coherence function g ¹ for various pump intensities and temperatures in the range of 1–20 K. Bistability and hysteresis in the dependence of the first-order coherence function on the pump intensity is demonstrated.     

Harnessing Quantumness of States using Discrete Wigner Functions under (non)-Markovian Quantum Channels

The negativity of the discrete Wigner functions (DWFs) is a measure of non-classicality and is often used to quantify the degree of quantum coherence in a system. The study of Wigner negativity and its evolution under different quantum channels can provide insight into the stability and robustness of quantum states under their interaction with the environment, which is essential for developing practical quantum computing systems. The variation of DWF negativity of qubit, qutrit, and two-qubit systems under the action of (non)-Markovian random telegraph noise (RTN) and amplitude damping (AD) quantum channels is investigated. Different negative quantum states that can be used as a resource for quantum computation and quantum teleportation are constructed. The success of quantum computation and teleportation is estimated for these states under (non)-Markovian evolutions.