Tripod型双电磁诱导透明原子系统中压缩光的传输（英文）

采用海森堡-朗之万方法理论研究了Tripod型双电磁诱导透明原子系统中压缩态探针场的传输特性.研究结果表明:通过双透明窗口压缩光可实现双通道传输,且每个通道可以被独立操控;当两束耦合场的频率失谐相等时,输出探针场的压缩度可以得到更好的保持.此外,输出探针场的压缩度可以通过耦合场的拉比频率、原子的光学厚度和基态退相干率以及探测频率来操控.该研究结果为进一步优化多通道量子存储提供依据.     

电磁感应双光子带隙的产生和控制

基于电磁感应透明技术, 通过求解原子的密度矩阵方程和电磁场的传输矩阵方程, 研究了被行波场和驻波场共同耦合的一个四能级冷原子介质的稳态光学特性, 发现在特定参数下能够产生一个几乎完美的双光子带隙结构, 在这两个光子带隙对应的频率区域内反射率都均匀地超过95%. 通过改变耦合场的强度和频率, 可以方便地调节这两个光子带隙的位置和宽度. 这一双光子带隙结构可用来实现全光路由和全光开关, 有望在全光信息网络中获得应用.     

级联四波混频系统中纠缠增强的量子操控

各类系统中的纠缠操控是量子信息科学的重要问题之一.本文研究了热原子蒸气的级联四波混频过程中产生的纠缠增强及纠缠增强的相位敏感特性.研究表明,该级联四波混频过程第二级输出的探针光和共轭光的量子纠缠较第一级明显增强,最大可达5 dB以上,且随着强度因子的增大可实现完美纠缠.文中还详细讨论了量子关联类型及纠缠大小与抽运光相位、非线性强度因子之间的变化关系,结果显示,由于纠缠增强及纠缠类型对抽运光相位的敏感性,通过控制相位和强度因子可改变光场噪声特性从而实现对探针光和耦合光之间纠缠增强、纠缠度大小、纠缠类型的量子操控.该理论研究对实验实现纠缠增强及双模压缩态压缩角、压缩度的光学参量操控具有重要的指导意义.     

激光线宽对原子相干效应的影响

该文在λ型三能级原子系统中分别讨论了耦合场和探针场线宽对电磁诱导透明(EIT)的影响,通过实验观测探针光和耦合光线宽变化时EIT的透明窗口的变化,得出耦合光对EIT的影响大于探针光线宽的影响,这一结果将为原子存储时间的提高具有一定意义.     

光泵浦效应对电磁诱导透明介质极化特性的影响

本文主要研究光泵浦效应对电磁诱导透明介质极化特性的影响。理论分析了耦合场分别与探针场同向和反向传播时,介质对探针场的色散和吸收特性。同时理论分析表明,相对二能级原子来说,由于耦合光的泵浦作用,在多普勒吸收基础上,原子对探针光的吸收增强,并且这种泵浦作用与耦合场传播方向无关。实验上验证了上述理论研究中原子介质对探针场的吸收特性。进一步地,实验研究了耦合光功率、频率失谐及粒子数密度等参量对泵浦率的影响,特别是对吸收宽度和深度的影响。     

双光子过程中任意初态原子的信息熵压缩

运用量子信息熵理论研究了双光子过程中任意初态二能级原子与相干场相互作用的信息熵压缩，讨论了系统初态对原子信息熵压缩的影响. 并且比较了分别从基于信息熵不确定关系和海森伯不确定关系出发得出的结果. 结果表明通过选择适当初始的原子分布角，原子的混合度和相干场的位相角，可以分别控制原子信息熵压缩的偶极矩分量数、压缩频率、压缩幅度和压缩方向. 当原子反转为零时，基于海森堡不确定关系的方差压缩定义不再有效，而信息熵压缩实现了对原子压缩效应的高灵敏量度. 关键词： 二能级原子 双光子过程 信息熵压缩 方差压缩     

双模压缩真空场与耦合双原子相互作用系统中光场的量子特性

研究了双模压缩真空场与耦合双原子系统中光场的压缩性质和相干性质.讨论了光场的初始压缩因子、原子-场耦合常数及原子间偶极-偶极相互作用常数对光场量子特性的影响. 关键词： 双模压缩真空场 耦合双原子系统 光场的非经典性质     

在Λ型三能级原子系统中实现光减速及光存储

在充缓冲气体的87Rb原子样品中, 通过探针光、耦合光与Λ型三能级原子相互作用过程中的量子干涉效应,产生了窄线宽的EIT透明窗口,由此实现了探针光群速度的降低.在最好的实验参数条件下,探针光群速度降低到c/42000.同时,研究了光群速减慢与介质温度、耦合光功率以及单光子频率失谐量之间的关系.在此基础上,通过控制耦合光与探针光的通断,实现了光脉冲在原子蒸汽中的存储与读取.     

利用Akaike信息准则研究退相位对量子干涉的操控作用

量子干涉(QI)和Autler-Townes分裂(ATS)是原子-光相互作用系统中的两种不同效应。在电磁诱导透明(EIT)系统中,当耦合光强度适中时,二者会同时存在。一般以耦合光拉比频率作为定性区分QI与ATS的依据,同时Akaike信息准则(AIC)可用于量化二者的相对权重。本文基于AIC方法研究了原子系统中退相位对QI和ATS权重的操控作用。研究表明,通过调节退相位率,可以实现QI和ATS之间的相互转换,以及相消干涉和相长干涉之间的相互转变。利用耦合光和探针光之间的相位关联可以实现退相位的精确操控,由此改变QI和ATS的权重,进而达到QI效应的极大增强。     

依赖于时间和强度耦合J-C模型中原子偶极压缩特性

研究了依赖于时间和强度耦合J-C模型中原子的偶极压缩现象。并详细讨论了原子与腔场以时间脉冲形式耦合时,脉冲宽度和腔场强度对原子算符压缩的影响。结果表明,在此模型下原子的偶极压缩随时间的演化特性与其他强度耦合模型明显不同,而且可以通过调节脉冲宽度有效控制原子的偶极压缩程度。     

Phase control of squeezed state in double electromagnetically induced transparency system with a loop-transition structure

We theoretically study the squeezed probe light passing through a double electromagnetically induced transparency (DEIT) system, in which a microwave field and two coupling lights drive a loop transition. It is shown that the output squeezing can be maintained in both two transparency windows of DEIT, and it can also be manipulated by the relative phase of the three driving fields. The influence of the intensity of applied fields and the optical depth of atoms on the squeezing is also investigated. This study offers possibilities to manipulate the squeezing propagation in atomic media by the phase of electromagnetic fields.     

Squeezing and entanglement of a two-mode field in a four-level tripod atomic system

The interaction of a collection of N four-level tripod configuration atoms with two orthogonally polarized probe fields is investigated. Under the condition of electromagnetically induced transparency (EIT), we calculate the squeezing and entanglement spectra of the output probe fields. By analyzing the output spectrum, we find that the squeezing and entanglement of the probe fields can be well-preserved after passing through the optically thick medium. Additionally, the effects of the ground state dephasing rates of the atoms on the entanglement and squeezing of the output two-mode squeezed fields are investigated. It is shown that the dephasing rates will degrade the entanglement and squeezing, and these quantum properties can be lost when the dephasing rates increase up to a certain value. This will be useful in the quantum computation and quantum communication.     

Local Modulation of Double Electromagnetically Induced Transparency Spectrum

The double electromagnetically induced transparency induced by two coupling fields can be realized in a fourlevel tripod-type atom. Such double transparency spectra can be locally modulated by using the weak coherent fields to perturb the coupling transitions. These investigations within this scheme can be independent of Doppler broadening by properly orienting these fieds.     

The difference in noise property between the Autler-Townes splitting medium and the electromagnetically induced transparent medium

The quantum noise of squeezed probe light passing through an atomic system with different electromagnetically induced transparency and Autler-Townes splitting effects is investigated theoretically.It is found that the optimal squeezing preservation of the outgoing probe beam occurs in the strong-coupling-field regime rather than in the weakcoupling-field regime.In the weak-coupling-field regime,which was recently recognized as the electromagnetically induced transparency regime(Abi-Salloum T Y 2010 Phys.Rev.A 81 053836),the output amplitude noise is affected mainly by the atomic noise originating from the random decay process of atoms.While in the strong-coupling-field regime,defined as the Autler-Townes splitting regime,the output amplitude noise is affected mainly by the phase-toamplitude conversion noise.This is useful in improving the quality of the experiment for efficient quantum memory,and hence has an application in quantum information processing.     

Coherent manipulation of spin squeezing in atomic Bose-Einstein condensate via electromagnetically induced transparency

We propose a scheme to coherently control spin squeezing of atomic Bose-Einstein condensate (BEC) via the technique of electromagnetically induced transparency (EIT). We study quantum dynamics of the mean spin vector and spin squeezing. It is shown that the mean spin vector and spin squeezing of the BEC can be controlled and manipulated by adjusting the external coupling fields or/and internal nonlinear interactions of the BEC. It is indicated that the spin squeezing can be generated rapidly in the dynamical process and maintained in a long time interval. It is found that a larger effective Rabi coupling between atoms and lasers can produce a stronger spin squeezing, and the squeezing can maintain a longer time interval.     

The difference in noise property between the Autlerben Townes splitting medium and the electromagnetically induced transparent medium

The quantum noise of squeezed probe light passing through an atomic system with different electromagnetically induced transparency and Autler-Townes splitting effects is investigated theoretically. It is found that the optimal squeezing preservation of the outgoing probe beam occurs in the strong-coupling-field regime rather than in the weak-coupling-field regime. In the weak-coupling-field regime, which was recently recognized as the electromagnetically induced transparency regime (Abi-Salloum T Y 2010 Phys. Rev. A bf81 053836), the output amplitude noise is affected mainly by the atomic noise originating from the random decay process of atoms. While in the strong-coupling-field regime, defined as the Autler-Townes splitting regime, the output amplitude noise is affected mainly by the phase-to-amplitude conversion noise. This is useful in improving the quality of the experiment for efficient quantum memory, and hence has an application in quantum information processing.     

Electromagnetically Induced Transparency and Absorption of A Monochromatic Light Controlled by a Radio Frequency Field

Electromagnetically induced transparency and absorption of a monochromatic light controlled by a radio frequency field in the cold multi-Zeeman-sublevel atoms are theoretically investigated. These Zeeman sublevels are coupled by a radio frequency(RF) field. Both electromagnetically induced transparency and electromagnetically induced absorption can be obtained by tuning the frequency of RF field for both the linear polarization and elliptical polarization monochromatic lights. When the transfer of coherence via spontaneous emission from the excited state to the ground state is considered, electromagnetically induced absorption can be changed into electromagnetically induced transparency with the change of intensity of radio field. The transparency windows controlled by the RF field can have potential applications in the magnetic-field measurement and quantum information processing.     

Probing decoherence with electromagnetically induced transparency in superconductive quantum circuits

Superconductive quantum circuits comprise quantized energy levels that may be coupled via microwave electromagnetic fields. Described in this way, one may draw a close analogy to atoms with internal (electronic) levels coupled by laser light fields. In this Letter, we present a superconductive analog to electromagnetically induced transparency that utilizes superconductive quantum circuit designs of present day experimental consideration. We discuss how a superconductive analog to electromagnetically induced transparency can be used to establish macroscopic coherence in such systems and, thereby, be utilized as a sensitive probe of decoherence.     

Frequency‐sensitive switching control effect induced by two‐photon resonance in an EIT‐based layered medium

The optical response of an atomic vapor can be coherently manipulated by tunable quantum interference occurring in atomic transition processes. A periodic layered medium whose unit cells consist of a dielectric and an EIT (electromagnetically induced transparency) atomic vapor is designed for light propagation manipulation. Such an EIT‐based periodic layered medium exhibits a flexible frequency‐sensitive optical response, where a very small change in probe frequency can lead to a drastic variation of reflectance and transmittance. As the destructive quantum interference relevant to two‐photon resonance arises in EIT atoms interacting with both control and probe fields, the controllable optical processes that depend sensitively on the external control field will take place in this EIT‐based periodic layered medium. Such a frequency‐sensitive and field‐controlled optical behavior of reflection and transmission in the EIT photonic crystal can be applicable to designs of new devices such as photonic switches, photonic logic gates and photonic transistors, where one laser field can be controlled by the other one, and would have potential applications in the areas of integrated optical circuits and other related techniques (e.g., all‐optical instrumentations).     

Simultaneous electromagnetically induced transparency and absorption in thermal atomic medium

A three-level lambda system driven by multicolor control, pump, and probe fields is investigated. The pump and probe fields are derived from the same laser with opposite propagating directions. Due to the Doppler effect, the zero group-velocity atoms face bichromatic fields, while other atoms face trichromatic fields. The atomic medium shows distinct characteristics and exhibits simultaneous electromagnetically induced transparency(EIT) and electromagnetically induced absorption(EIA) at two frequencies. EIT and EIA peaks have a fixed relationship with frequency, which is determined by the Doppler shifts.