量子点腔非谐振耦合系统纯退相干的特性及应用

采用非相干泵浦、受激辐射和纯退相干的量子主方程研究了量子点腔耦合系统,得出腔与量子点发射光谱解析解.理论分析显示,在非谐振耦合系统中纯退相干能使腔发射谱产生明显的移位效应,从而可以解释“非谐振耦合腔有效发射”效应.为了进一步研究纯退相干在量子点腔耦合系统上的应用,引入了系统有效耦合率和单光子源效率,并通过比较有效耦合率与腔耗散定义出好腔与坏腔机制.选取两组依据实验数据作为参量,在共振与失谐时研究了纯退相干对系统有效耦合率和单光子源效率的影响.结果表明:纯退相干可提高失谐系统有效耦合率与单光子源效率,从而可能使坏腔转变为好腔|两组参量中有较大耦合效率一组在一定范围内满足好腔机制,其单光子源效率明显优于另一组.在非谐振耦合系统比较了好腔机制与坏腔机制的激光,好腔机制是实现单量子点激光的必要条件|由于非谐振耦合系统Fano因子无最大值出现,从而该系统可能无激光阈值.     

量子点腔系统中抽运诱导受激辐射与非谐振腔量子电动力学特性的研究

从量子点和腔相互作用的哈密顿量出发,利用包括非相干抽运,退相干项主方程,并结合量子回归定理,考虑相关初始条件,理论推导和数值计算相结合得出量子点多光子发射光谱精确数值结果.分析多光子发射光谱(费米子统计)和相应单光子情况(玻色子统计)时,得到依据费米子统计,退相干和热浴模型的多光子发射光谱同最近文献[22]量子点——微柱腔实验结果符合得非常好.结合理论和当前实验,显示了量子点腔系统中抽运诱导受激辐射和非谐振腔量子电动力学. 关键词： 量子点 微腔 受激辐射 发射光谱     

Collective spontaneous emission of dye molecules and lasing

The threshold pump power density for lasing in dye solutions is found to depend on the photon energy of pumping radiation. An increase in the pumping photon energy can significantly lower the threshold pump power of dye lasers. For an ethanol solution of rhodamine 6G with a concentration of 4×10¹⁸ cm^?3, the threshold power density for pumping radiation with a wavelength of 532 nm is 20-fold higher than for pumping radiation with a wavelength of 347 nm. This phenomenon is associated with the competition of collective spontaneous emission, which can lead to the efficient deactivation of excited molecules in femtosecond times, and the dephasing of excited molecules due to the intramolecular nonradiative processes of absorbed-energy conversion. An increase in the dephasing rate with the increasing energy of exciting photons lowers the efficiency of collective spontaneous emission and increases the concentration of dephased excited molecules responsible for lasing.     

Steady state Behaviour of a Three level Ladder Atomic System with Incoherent Population Pumping in a Squeezed Vacuum

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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.     

光抽运双光子激光朗之万量子理论

本文采用朗之万量子理论获得光抽运双光子激光具有双光子损耗时的朗之万方程,进一步获得稳态平均光子数、频率牵引、线宽和动态斯塔克效应,对激光增益来源的分析表明,非相干抽运仅有单双光子两步过程有贡献,而相干抽运,除上述过程外还有单双光子一步过程有贡献,而且,上述两个过程都受到负反馈和饱和因子的制约,线宽与稳态平均光子数无关。 关键词：     

Multilevel,multifrequency laser pulse propagation

We give a nonperturbative method for calculating the complex index of refraction for each of several optical fields interacting with a multilevel system, and illustrate the method by calculating the gain and absorption on an optically pumped, nearly resonant Raman transition as functions of the laser frequencies and fields, including the effects of dephasing and incoherent pumping of populations.     

Efficient single-photon generator based on entanglement between the emitter and field in a photonic crystal near the band edge

The possibility of using the long-lived entangled state between the emitter and field near the band edge of the density of states of a photonic crystal to create an efficient generator of single photons is considered. The generator can be efficiently excited by incoherent pumping, excludes simultaneous generation of two photons, and ensures a high probability of extracting the photon into a specified mode.     

Dependence of cooperative emission spectra of complex organic molecules on exciting photon energy

The dependences of cooperative emission, superfluorescence, and lasing spectra on the wavelength of pumping radiation were studied for highly concentrated ethanol solutions of organic dye molecules. The relative intensity of cooperative emission was found to decrease, while the intensities of superfluorescence and lasing were found to increase with the energy of exciting photons. The increase in the dephasing rate of quantum states is supposed to be primarily responsible for the change in proportion between these intensities. On increasing the dephasing rate, with all other factors being the same, the concentration of the excited molecules with the phased quantum states decreases, while that with the dephased states increases. The ratio between the cooperative emission and dephasing rates determines the proportion between the intensities of cooperative emission, superfluorescence, and lasing. The onset of lasing at high concentrations (above >10¹⁹ cm^?3) in the case of pumping by high-energy photons occurs due to the high dephasing rates of quantum states resulting from a more rapid redistribution of vibrational energy.     

利用光纤中自发四波混频产生纠缠光子的实验装置

基于三阶非线性Kerr效应在光纤中产生非线性现象的理论,利用零色散位移光纤中的自发四波混频通过两种实验装置产生了纠缠光子：一种是采用脉冲光抽运由光纤构成的Sagnac光纤环;另一种是采用脉冲光直接抽运一段光纤.通过对不同装置下实验结果的比较,总结了产生高纯度纠缠光子所需的实验条件,并指出了两种装置各自的优缺点.这为研制适用于量子通信的全光纤纠缠光源和单光子源奠定了基础. 关键词： 纠缠光子 光纤 四波混频 量子通信     

Photon echoes in an amplifying rare-earth-ion-doped crystal

We report what we believe is the first experimental demonstration of photon echoes in an amplifying rare-earth-ion-doped crystal. Population inversion is achieved by optical pumping, which yields high-power photon echoes, with an energy gain of as much as a factor of 5. Effects of the pump on the photon echo process highlight the advantages of an amplifying crystal. New questions concerning the optical dephasing mechanisms in Er3+:YSO have arisen.     

微腔中单量子点的激光输出特性研究

研究一个四能级量子点耦合到单模光学腔中的量子系统,利用系统的主方程作数值模拟计算微腔中单量子点的激光输出强度随非相干泵浦的变化关系.结果显示量子点在泵浦作用下激光的输出有一个阈值;且量子点和腔模耦合强度增强时,产生激光的阈值明显减小,输出激光的峰值却增大.当泵浦作用继续增强到一定程度,因激光能级间的相干性被过强的非相干泵浦所破坏,单量子点激光输出变为零----出现了淬灭现象.     

Probing noise in flux qubits via macroscopic resonant tunneling

Macroscopic resonant tunneling between the two lowest lying states of a bistable rf SQUID is used to characterize noise in a flux qubit. Measurements of the incoherent decay rate as a function of flux bias revealed a Gaussian-shaped profile that is not peaked at the resonance point but is shifted to a bias at which the initial well is higher than the target well. The rms amplitude of the noise, which is proportional to the dephasing rate 1/tauphi, was observed to be weakly dependent on temperature below 70 mK. Analysis of these results indicates that the dominant source of low energy flux noise in this device is a quantum mechanical environment in thermal equilibrium.     

Artificial atoms can do more than atoms: deterministic single photon subtraction from arbitrary light fields

We study the interplay of photons interacting with an artificial atom in the presence of a controlled dephasing. Such artificial atoms consisting of several independent scatterers can exhibit remarkable properties superior to single atoms with a prominent example being a superatom based on Rydberg blockade. We demonstrate that the induced dephasing allows for the controlled absorption of a single photon from an arbitrary incoming probe field. This unique tool in photon-matter interaction opens a way for building novel quantum devices, and several potential applications such as a single photon transistor, high fidelity n-photon counters, or the creation of nonclassical states of light by photon subtraction are presented.     

基于量子点接触的开放双量子点系统电子转移特性

基于量子点接触探测器(QPC)理论上研究了双量子点(DQD)系统在耗散环境和纯退相环境影响下的电子转移特性.结果表明,耗散环境中探测器导致的退相干会增大平均电流和Fano factor随时间演化的值,并观察到量子芝诺效应的存在.在对称的DQD情况下,弛豫减小了平均电流随时间演化的震荡振幅.在非对称的DQD情况下,弛豫降低了Fano factor随时间演化的峰值.纯退相环境中测量会阻碍共隧穿过程中不同电流通道之间的转换,导致Fano factor的极高值.在对称的DQD情况下,增大纯退相速率会提高Fano factor.在非对称的DQD情况下,动力学随时间的演化对纯退相环境不敏感.另外,还发现探测器内n个电子的转移几率只受QPC与DQD耦合的影响.我们的结论可以为实验工作者研究电子输运特性提供理论参考.     

General quantum mechanical theory of pure dephasing

We consider the pure dephasing of a two-level system interacting linearly and quadratically with a bath of harmonic oscillators; the system studied is the most general harmonic two-surface problem. The temperature-dependent pure dephasing rate is calculated exactly to all orders in the system-bath interaction. Often this interaction can be expressed in terms of a small number of collective coordinates (linear combinations of bath modes). For the case of two such coordinates, we provide explicit expressions for the dephasing rate. If there is only a single collective coordinate, we recover our result from previous publications.     

Optical bistability via quantum interference from incoherent pumping and spontaneous emission

We theoretically investigate the optical bistability (OB) in a V-type three-level atomic system confined in a unidirectional ring cavity via incoherent pumping field. It is shown that the threshold of optical bistability can be controlled by the rate of an incoherent pumping field and by interference mechanism arising from the spontaneous emission and incoherent pumping field. We demonstrate that the optical bistability converts to optical multi-stability (OM) by the quantum interference mechanism.     

Manipulation of tunneling induced transparency windows and optical switching features in fivefold quantum dot molecules

Transient and steady-state behavior of the probe absorption in a multiple quantum dot (QD) molecule composed of five quantum dots molecules (with a center dot and four satellite dots) is explored with application in all-optical switching. We find that the absorption spectra of the light pulse can be efficiently modified via the effect of inter-dot tunnel couplings of QDs and incoherent pumping field. Results show that depending on the values of system parameters, at least one and at most four tunneling induced transparency (TIT) windows can be established in the multiple QD medium. We then investigate the dynamical behavior of the probe absorption-amplification as well as the optical switching in pulsed regime. By adjusting the incoherent pumping rate, the required switching time for changing the gain to the absorption or vice versa is then estimated approximately to be 20.7 nanosecond (ns), that is an appropriate time for such a QDM-based switch.     

超低温下掺Er3+玻璃的相干拍频调制效应研究

采用非相干光时延四波混频(TDFWM-IL)实验装置,在7K温度下,利用波长为800 nm的飞秒脉冲激光,观测到掺Er3+玻璃的光子回波效应,发现信号随延时变化的拍频调制结构.根据TDFWM-IL多能级理论,运用其非均匀加宽占主导时的公式拟合实验结果,从最佳拟合获得的退相时间T2=300 fs,这与由相干控制实验测得的...