混沌光场光子统计分布及二阶相干度的分析与测量

利用通信波段双通道单光子探测器,采用Hanbury Brown-Twiss关联测量方案,理论分析并实验测量了光反馈半导体激光器产生的混沌光场的光子统计分布及不同混沌状态光场的二阶相干度.通过对混沌光场二阶相干度g~((2))(τ)的理论分析,得出随着延迟时间和相干时间的变化,其与相干光、热光及单光子态的二阶相干度可明显区分并呈现出不同分布.同时实验上产生了频谱宽度6.7 GHz的混沌光场,测量了不同光子数分布的结果,并用高斯随机分布、泊松分布、玻色-爱因斯坦分布对光子数分布进行理论拟合,发现随着入射平均光子数的增加,光子数分布从玻色-爱因斯坦分布过渡到泊松分布,但整个过程都与高斯随机分布符合较好,且光场的二阶相干度g~((2))(0)由2降至1.通过改变偏置电流(I=1.0Ith-2.0Ith)和反馈强度(0—10%),实验上研究了混沌光场由低频起伏到相干塌陷的过程中不同状态宏观动力学特性与二阶相干度的对应关系.结果表明:混沌光场在此过程中始终呈现出明显的聚束效应,并在频谱宽度最大时达到最强;同时给出了光子计数测量中聚束效应减弱的物理原因.实验表明该系统及方法能很好地揭示不同状态混沌光场的光子统计特性.     

Microwave control of transport through a chaotic mesoscopic dot

We establish analogy between a microwave ionization of Rydberg atoms and a charge transport through a chaotic quantum dot induced by a monochromatic field in a regime with a potential barrier between dot contacts. We show that the quantum coherence leads to dynamical localization of electron excitation in energy so that only a finite number of photons is absorbed inside the dot. The theory developed determines the dependence of localization length on dot and microwave parameters showing that the microwave power can switch the dot between metallic and insulating regimes. ultiphoton ionization and excitation to highly excited states (e.g., Rydberg states)     

Coherence of a squeezed sodium atom laser generated from Raman output coupling

The coherence of a squeezed sodium atom laser generated from a Raman output coupler, in which the sodium atoms in Bose-Einstein condensate （BEC） interact with two light beams consisting of a weaker squeezed coherent probe light and a stronger classical coupling light, is investigated. The results show that in the case of a large mean number of BEC atoms and a weaker probe light field, the atom laser is antibunching, and this atom laser is second-order coherent if the number of BEC atoms in traps is large enough.     

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.     

Decay of quantum correlations in atom optics billiards with chaotic and mixed dynamics

We perform echo spectroscopy on ultracold atoms in atom-optics billiards to study their quantum dynamics. The detuning of the trapping laser is used to change the "perturbation", which causes a decay in the echo coherence. Two different regimes are observed: first, a perturbative regime in which the decay of echo coherence is nonmonotonic and partial revivals of coherence are observed in contrast with the predictions of random matrix theory. These revivals are more pronounced in traps with mixed dynamics as compared to traps where the dynamics is fully chaotic. Next, for stronger perturbations, the decay becomes monotonic and independent of the strength of the perturbation. In this regime no clear distinction can be made between chaotic traps and traps with mixed dynamics.     

Effect of quantum fluctuations on the dipolar motion of bose-einstein condensates in optical lattices

We reexamine dipolar motion of condensate atoms in one-dimensional optical lattices and harmonic magnetic traps including quantum fluctuations within the truncated Wigner approximation. In the strong tunneling limit we reproduce the mean field results with a sharp dynamical transition at the critical displacement. When the tunneling is reduced, on the contrary, strong quantum fluctuations lead to finite damping of condensate oscillations even at infinitesimal displacement. We argue that there is a smooth crossover between the chaotic classical transition at finite displacement and the superfluid-to-insulator phase transition at zero displacement. We further analyze the time dependence of the density fluctuations and of the coherence of the condensate and find several nontrivial dynamical effects, which can be observed in the present experimental conditions.     

半导体光放大光纤环形激光器的偏振混沌与相干性

研究了基于半导体光放大器(SOA)的光纤环形激光器的偏振混沌光的特性及其相干性。实验采集激光器的输出功率和偏振度,得到了基于半导体光放大器的光纤环形激光器的输出从自发辐射到受激辐射、再到偏振态混沌激光辐射的演化过程。利用马赫-曾德尔(M-Z)干涉仪验证了混沌激光的相干性,并发现混沌干涉只有零级。测量不同光程差时干涉仪的输出功率,计算相应的干涉条纹可见度,进一步算得混沌激光的相干时间约为40 ps。这一结果与根据光谱计算的该混沌激光的相干时间43 ps基本一致。实验还测得该混沌激光的相干性与半导体光放大器的电流无关。并指出了混沌激光相干应用于低相干光源探测领域的灵敏度和分辨力优势。     

Synchronization and coherence resonance in chaotic neural networks

Synchronization and coherence of chaotic Morris--Lecar (ML) neural networks have been investigated by numerical methods. The synchronization of the neurons can be enhanced by increasing the number of the shortcuts, even though all neurons are chaotic when uncoupled. Moreover, the coherence of the neurons exhibits a non-monotonic dependence on the density of shortcuts. There is an optimal number of shortcuts at which the neurons' motion is most ordered, i.e. the order parameter (the characteristic correlation time) that is introduced to measure the coherence of the neurons has a maximum. These phenomena imply that stochastic shortcuts can tame spatiotemporal chaos. The effects of the coupling strength have also been studied. The value of the optimal number of shortcuts goes down as the coupling strength increases.     

Onset of coherent oscillations in turbulent Rayleigh-Bénard convection

We report temperature cross correlation and velocity profile measurements in the aspect-ratio-one convection cell filled with water. A sharp transition from a random chaotic state to a correlated turbulent state of finite coherence time is found when the Rayleigh number becomes larger than a critical value Ra(c) approximately equal to 5 x 10(7). The experiment reveals a unique mechanism for the onset of coherent oscillations in turbulent Rayleigh-Bénard convection.     

Influence of chaotic pump radiation with finite bandwidth on the intensity correlation of resonance fluorescence radiation

It is shown that the bandwidth of chaotic pump radiation can strongly influence the behavior of the intensity correlation of resonance fluorescence in contrast to a laser pump. This different behavior arises from the different higher order coherence properties of chaotic and laser light with the same bandwidth.     

Effects of Atomic Coherence and Injected Classical Field on Chaotic Dynamics of Non-degenerate Cascade Two-Photon Lasers

Based on the cascade two-photon laser dynamic equation derived with the technique of quantum Langevin operators with the considerations of coherently prepared three-level atoms and the classical field injected into the cavity, we numerically study the effects of atomic coherence and classical field on the chaotic dynamics of a two-photon laser. Lyapunov exponent and bifurcation diagram calculations show that the Lorenz chaos and hyperchaos can be induced or inhibited by the atomic coherence and the classical field via crisis or Hopf bifurcations.     

Effects of Atomic Coherence and Injected Classical Field on Chaotic Dynamics of Non-degenerate Cascade Two-Photon Lasers

Based on the cascade two-photon laser dynamic equation derived with the technique of quantum Langevin operators with the considerations of coherently prepared three-level atoms and the classical field injected into the cavity, we numerically study the effects of atomic coherence and classical field on the chaotic dynamics of a two-photon laser. Lyapunov exponent and bifurcation diagram calculations show that the Lorenz chaos and hyperchaos can be induced or inhibited by the atomic coherence and the classical field via crisis or Hopf bifurcations.     

Superradiant light scattering from thermal atomic vapors

Superradiant light scattering from noncondensed, thermal atomic vapors was experimentally studied. We found that superradiant gain is independent of quantum degeneracy and determined only by the shape of the atomic cloud and a contained number of atoms. Superradiant pump-probe spectroscopy was also developed to measure the atomic correlation function, revealing the Doppler-width-limited coherence time of the thermal gas and sudden buildup of long-lived coherence below the transition temperature.     

Quantum decoherence due to non-linear dynamics of environment

We discuss quantum decoherence in an open system which couples with a non-linear environment with finite degrees of freedom. Even if the degrees of freedom of the environment are finite, the strong non-linearity of the environment is expected to destroy quantum coherence of the open system like a heat bath with infinite degrees of freedom. In order to demonstrate this fact, we use two-dimensional kicked rotors as the environment and investigate a master equation for a reduced density matrix which is obtained by coarse-graining the environmental degrees of freedom. Our numerical simulation shows that when the non-linearity of the environment exceeds a critical strength, quantum coherence of the open system is irreversibly destroyed. This decoherence is due to the uncorrelated response of the environment to the open system and is related to the chaotic property of the non-linear environment.     

Coherence and stacking interaction in DNA duplex

It is shown that a chaotic (deterministic) order, rather than a stochastic randomness, controls the energy minima positions of the stacking interactions in the DNA sequences on large-scales. The chaotic order results in a long-range chaotic coherence between the two complimentary DNA-duplex?s strands. A competition between this broad-band chaotic coherence and the resonance coherence produced by genetic code has been briefly discussed.     

Zur Korrelationsfunktionn-ter Ordnung für die Überlagerung von Thermischem und Kohärentem Licht

Then-th order correlation function for superimposed coherent and chaotic light is calculated in coherent state formalism. This function reduces to products and sums of the first-order correlations of coherent and chaotic fields alonge. It is demonstrated that superimposed fields cannot have full coherence farther then to the first order.     

Laser-induced chemistry-basic nonlinear processes and applications

Many methods and achievements in chemistry are based on using the interactive of light with atoms and molecules. It is sufficient to mention photochemistry, flashphotolysis, spectrochemistry and others. The advent of laser amplified the connection between chemistry and light. Today laser light has become a very versatile and effective tool, first, to study the dynamics of chemical reactions, secondly, to stimulate chemical reactions and finally, to analyze substance. The unique properties of laser light (high power, monochromaticity, short duration, directivity and temporal coherence) provide quite new instrumental possibilities in all these problems.     

两纠缠原子与相干态光场相互作用过程中光场的量子特性

采用时间演化算符和数值计算方法,研究了两全同二能级纠缠原子与相干态光场相互作用过程中光场的量子特性,结果表明:两原子初始纠缠度和相干态光场强度对系统光场的二阶相干性质和压缩效应有很大的影响.     

Generation of light carrying orbital angular momentum via induced coherence grating in cold atoms

We report on the generation of light carrying orbital angular momentum through Bragg diffraction into an electromagnetically induced coherence grating in a degenerate two-level system of cold cesium atoms. The induced Zeeman coherence grating is shown to contain the spatial phase structure of the incident beams. The exchange of phase information between a light beam with orbital angular momentum and a long-lived atomic coherence opens up the way to process quantum information encoded in a multidimensional state space.     

Optical pumping experiments using a cw dye laser with a narrow spectral output

An optical pumping experiment on the Na atoms of an atomic beam by means of a continuous wave dye laser is described. The atoms interact at two different regions with the laser beam. In the first region the atoms are optically pumped so that a Zeeman coherence in their substates is produced. In the second light beam the coherence is probed. Any changes in the phase of the eigenfunction of the atom through interaction in a magnetic field, or through collisions, or other effects occuring in the light free section can thus be sensitively detected. The possible applications of the set-up are discussed.