理想腔中多次原子注入产生的光场挤压

利用共振的Jaynes-Cummings(缩写为J-C)模型研究腔内相干光场与原子多次作用后所产生挤压效应。在单光子跃迁情况,对适当选取的小的作用时间,通过多次作用可以提高压缩度,但有限制,次数太多,压缩反而变坏。在双光子跃迁情况,对于强相干光和适当取值的作用时间t=π/g₂,可以求出被压缩的不确定度与作用次数间的解析关系式。此式表明,选取适当的作用次数可以得到深度压缩。初始平均光子数N愈大,能达到的最大压缩愈强。 关键词：     

稠密V型介质中双色飞秒脉冲及频谱演化的RCEP调制

利用不含慢变振幅近似和旋波近似的全波Maxwell-Bloch方程组的数值解,研究单光子共振和失谐两种条件下,相对载波包络相位(RCEP)对在稠密V型三能级原子介质中传播的双色sech型飞秒超短脉冲及频谱演化的影响.结果表明,RCEP对双色脉冲的传播形式及频谱特性的调制在失谐情况比在单光子共振情况显著,在失谐条件下调节RCEP可获得比单光子共振条件下大得多的频谱展宽,出现了最高频率达到入射脉冲中心频率18倍的超连续谱.     

光场与V型三能级原子依赖强度耦合系统场熵的演化特性

研究了光场与V型三能级原子依赖强度耦合系统场熵的演化特性,讨论了单光子跃迁失谐量和初始光子数对场熵演化的影响. 研究结果表明,当失谐量比较小且初始光场较弱时,场熵的时间演化行为与单光子Jaynes-Cummings模型相似; 当失谐量足够大或初始光场足够强时,场熵的时间演化表现出类似于双光子Jaynes-Cummings模型中场熵演化的周期性.     

光场与Ⅴ型三能级原子依赖强度耦合系统场熵的演化特性

研究了光场与v型三能级原子依赖强度耦合系统场熵的演化特性,讨论了单光子跃迁失谐量和初始光子数对场熵演化的影响.研究结果表明,当失谐量比较小且初始光场较弱时,场熵的时间演化行为与单光子JaynesCummings模型相似;当失谐量足够大或初始光场足够强时,场熵的时间演化表现出类似于双光子Jaynes-Cummings 模型中场熵演化的周期性.     

85Rb热原子系综中Raman相干存储的实验研究

报道了我们在85Rb热原子系统中利用远离共振的Raman动力学过程实现相干光信号存储与释放的实验研究.铷原子室采用μ-metal包裹消除环境磁场的影响,在双光子共振和单光子远失谐的条件下,我们测量了存储效率随存储时间及单光子失谐量的变化关系,得到的最高存储效率为23.5％,寿命约为3.4μs.     

H2O和HLi分子的双光子激发

用全相对论量子力学计算H2O和HLi的双光子偶极激发。为对比起见,同时用非相对论的对称匹配团族-组态相互作用法(SAC-CI)计算其单光子激发。对于无对称中心的H2O和HLi,符合相应群的对称选择原则。双光子跃迁几率一般比单光子跃迁的小3～5个数量级。在计算双光子偶极激发时,应采用同时包含了空间的对称性和时间反转对称性的全相对论。     

利用单光子和双光子共振电离增强He原子谐波强度

理论研究了He原子在吸收紫外光子后对高次谐波的强度的影响。结果表明：当紫外光光子能量满足He原子基态与激发态的单光子和双光子共振跃迁时,谐波强度有超过2个数量级的增强。当紫外光光子能量满足He原子基态与激发态的多光子共振跃迁时,谐波强度增强明显减弱。分析电离几率表明,单、双光子共振电离在紫外共振电离中起主要作用,因此导致谐波强度的明显增强。同时,在啁啾调频场的作用下谐波截止能量也明显延伸,可以获得一个强度较高的谐波光谱连续区。选取该谐波连续区可获得脉宽为40 as的孤立脉冲。     

缀饰原子系统中双光子共振非简并四波混频

本文研究了缀饰原子系统中的双光子共振非简并四波混频.理论上我们研究了多普勒增宽的四能级系统中耦合光场对双光子共振非简并四波混频的影响,发现加入强耦合场后,非简并四波混频频谱出现Autler-Townes分裂;在不同双光子共振失谐时,由于量子干涉双光子共振非简并四波混频的信号能够被抑制或增强.实验上我们在Ba原子蒸汽中,通过引入基态6s2和自电离里德堡态6pnd之间的原子相干证实了该现象.本方法提供了一种不仅可以测得共振频率和横向弛豫,而且可以测得两个高激发原子态之间的跃迁的偶极矩阵元的新的光谱学工具.     

H2X(X=O,S,Se,Te)分子的双光子激发

本文采用全相对论量子力学计算了H₂X (X=O, S, Se, Te) 分子的双光子过程, 并考虑相对论效应对双光子过程的影响. 结果表明, 各个不可约表示对称态下激发能有着明显的差异,它反应了双光子吸收过程中选择能级的特点. 同时, 采用非相对论的对称匹配簇/组态相互作用方法 (SAC-CI) 计算其分子的单光子激发, 并与之比较. 双光子跃迁概率要比单光子跃迁概率小2–5个数量级; 同一主族, 随着原子序数的增加, 相对论效应对分子体系的激发能量、跃迁概率、振子强度的大小都有显著地影响; 除此之外,每个分子遵守分子对称群的选择原则. 本文中, 分子H₂X (X=O, S, Se, Te) 的个别不可约表示对称态的跃迁矩分量和振子强度远远大于其他对称态下的跃迁矩分量和振子强度, 甚至大于单光子激发. 这不仅与分子的对称性有一定的关系, 而且应该是选择双光子跃迁能级的重要依据. 关键词： 全相对论量子力学 双光子激发 电偶极跃迁矩 振子强度     

在一个具有超精细结构的四能级原子系统中的拉曼散射

在一个具有超精细结构的四能级原子系统中，为了压抑暂态过程和稳态过程两种情况下的弱探测光束的吸收，我们提出和分析了一种有效的拉曼散射计划。对于暂态过程，借助一个漂亮的Mathematic程序进行数值计算，我们发现在探测跃迁线中心探测吸收的幅度与一般的基于电磁感应透明的三能级原子系统相比要小。对于稳态情况，结果表明探测吸收在线中心能够被彻底地消除，正像通常的三能级电磁感应透明方案。特别地，我们的结果表明在拉曼共振的条件下探测吸收能够被彻底地消除，也就是说，对于稳态过程我们仅仅要求双光子失谐量在超精细二能级频率间隙内是零。与标准的三能级电磁感应透明方案相比，我们的四能级拉曼计划的优点之一是在拉曼共振条件下我们能观察到透明窗口，不需要严格地单光子和双光子失谐量为零。因此，原子超精细结构对于获取电磁感应透明不是一个障碍。     

Enhancement of Squeezing in Two-Photon Jaynes-Cummings Model with Atomic Measurement

We investigate the squeezing properties of the cavity field in the degenerate two-photon Jaynes-Cummings model. Compared with the one-photon Jaynes-Cummings model, the squeezing is more pronounced in the case of two-photon Jaynes-Cummings model under certain conditions.     

Damping in the Interaction of a Two-Photon Field and a Two-Level Atom Through Quantized Caldirola-Kanai Hamiltonian

Following the lines of the recent papers (Daneshmand and Tavassoly, Int. J. Theor. Phys. 56, 1218 (2017)), we study quantum mechanical treatments of an interaction between a two-level atom with a single-mode field in the two-photon Jaynes-Cummings model, where the Hamiltonian of the field is considered to be the quantized Caldirola-Kanai (CK) Hamiltonian. As a result, we would expect that the quantum dynamics of the two-photon JCM in terms of the CK Hamiltonian is qualitatively different from that of the usual one-photon case. We analytically calculate the explicit form of the atom-field entangled state and numerically evaluate the dynamics of its physical properties. The degree of entanglement, atomic population as well as sub-Poissonian statistics and quadrature squeezing of the field are analyzed. We adjust the latter evolved parameters by appropriately tuning the damping parameter within the CK Hamiltonian and detuning factor. Finally, we report a field detuning asymmetry in the collective statistical behavior.

     

Simulation of a quantum NOT gate for a single qutrit system

A three-level system based an a three-level atom interacting with a detuned cavity is considered. Because of the fact that the three-level atom defines a total normalized state composed of superposition of three different single-level states, it is assumed that such a system implements a qutrit. In order to achieve a quantum NOT gate for a single qutrit, the respective Schrödinger equation is solved numerically within a two-photon rotating wave approximation. For small values of one-photon detuning, there appear decoherence effects. Meanwhile, for large values of one-photon detuning, an ideal quantum NOT gate for a single qutrit is achieved. An expression for the execution time of the quantum NOT gate for a single qutrit as a function of the one-photon detuning is found.     

二能级原子与压缩光场相互作用中的原子压缩效应

文中采用时间学业伦算符，考察到初始原子相干性及失谐量，研究了单个二能级原子与压缩真态辐射场相互作用中原子的偶极压缩。研究表明，对于各种不同的初始原子态，失谐量对双光子Ｊａｙｎｅｓ－Ｃｕｍｍｉｎｇｓ模型中的原子压缩行为都将产生很大的影响。通过数值计算，还讨论了初始压缩光场的压缩参数对原子压缩的影响。     

双光子失谐对慢光和光存储影响的实验研究

利用电磁感应透明(EIT)效应在87Rb热原子气室中进行了慢光和光存储的实验研究,在单光子红失谐650 MHz处测量了双光子失谐对光脉冲延迟和光存储的影响.结果表明:在双光子失谐0—0.5 MHz范围内存在显著的光脉冲延迟和光存储恢复信号,其慢光波形与理论计算结果基本相符;而恢复光脉冲信号随着双光子失谐的变化出现形变,这是由于多个EIT子系统之间的干涉引起的.这一研究结果为连续变量光场在热原子系综中的存储提供了实验参考.     

The Effect of Incoherent Population Pumping on Squeezing in Resonance Fluorescence

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The Effect of Incoherent Population Pumping on Squeezing in Resonance Fluorescence

The effect of incoherent population pumping on the steady-state population inversion and the quadrature squeezing spectra produced in the resonance fluorescence of a two-level atom is investigated. In the presence of incoherent population pumping, the steady-state population inversion is increased for small frequency detuning but is not changed for large frequency detuning. For resonant excitation at low intensities, the weak incoherent pumping degrades the degree of the squeezing and shifts the position of the maximum squeezing; for off-resonant excitation at strong intensities, the weak incoherent pumping hardly changes the squeezing spectra. But when the incoherent pumping is strong the squeezing may be completely destroyed for both cases.     

Ultrafast coherent population transfer driven by two few-cycle laser pulses

We investigate ultrafast coherent population transfer driven by few-cycle pump and Stokes laser pulses in the Λ-type three-level system with the stimulated Raman adiabatic passage technique beyond the rotating-wave approximation. In contrast to the case with the rotating wave approximation, the most efficient population transfer may be realized without the satisfaction of the one-photon resonances or two-photon resonance and the transfer efficiency depends critically on the Rabi frequencies and initial optical phases of the two laser fields when the peak Rabi frequencies are much larger than the respective transition frequencies. Moreover, complete and robust population transfer can still be obtained with the variations of the Rabi frequencies, pulse durations, and one-photon or two-photon detuning in a moderate range, though a considerable transient population may reside in the excited state. These abnormal behaviors result from the counterrotating terms, which are not taken into account in the traditional rotating wave approximation.     

良腔情况吸收与色散混合受驱动光学系统多光子过程压缩效应

本文讨论吸收与色散混合型多光子受驱动光学系统在良腔情况下场的压缩效应,得出在一定条件下,对于单光子过程,场量正交分量之一A₁在混合型比在纯吸收型具有更佳的压缩效应,而对于双光子过程,场量另一正交分量A₂也可能出现压缩效应。 关键词：