Dynamical properties of ultracold Bose atomic gases in one-dimensional optical lattices created by two schemes

An optical lattice could be produced either by splitting an input light(splitting scheme) or by reflecting the input light by a mirror(retro-reflected scheme).We study quantum dynamical properties of an atomic Bose–Einstein condensate(BEC) in the two schemes.Adopting a mean field theory and neglecting collision interactions between atoms, we find that the momentum and spatial distributions of BEC are always symmetric in the splitting scheme which, however, are asymmetric in the retro-reflected scheme.The reason for this difference is due to the local field effect.Furthermore, we propose an effective method to avoid asymmetric diffraction.     

Manipulation of optical fields by atomic interferometry: Quantum variations on a theme by young

We analyze the principle of a very general and conceptually simple method for manipulating optical fields by coupling them into a matter waves Young double slit apparatus. The field, non resonant with the atoms, acts as a phase-retarding medium in one of the arms of the interferometer and shifts the atomic fringe pattern. The method constitutes a simple quantum nondemolition measuring scheme of the photon number. Non classical states such as Schrödinger cats and Fock states of the field are generated in the measurement process. The analysis of the atomic interferometer with optical retarding fields provides a very simple and striking illustration of basic concepts of the quantum measurement theory and of the principle of complementarity. This scheme, which would be very difficult to implement in the optical domain, is equivalent to a more feasible and recently proposed Ramsey interference method to measure small microwave fields with beams of Rydberg atoms.Associé au Centre National de la Recherche Scientifique et à l'Université Pierre et Marie Curie     

强激光产生的强磁场及其对弓激波的影响

强激光照射金属线圈后,会在打靶点附近的背景等离子体中诱发冷电子的回流,在金属丝内形成强电流源,从而产生强磁场.本文利用神光II高功率激光器产生的强激光照射金属丝靶,产生了围绕金属丝的环形强磁场.利用B-dot对局域磁感应强度进行了测量,根据测量结果,结合三维模拟程序,反演得到磁场的空间分布.再利用强激光与CH平面靶相互作用产生的超音速等离子体撞击该金属丝,产生了弓激波.通过光学成像手段研究了磁场对冲击波的影响,发现磁场使得弓激波的轮廓变得不明显并且张角变大.同时,通过实验室天体物理定标率,将金属丝表面等离子参数变换到相应的天体参数中,结果证明利用该实验方法可以在实验室中产生类似太阳风的磁化等离子体.     

Non-classical correlation of the two emission fields by a four-level atomic ensemble

The normalized second-order correlation of the emission fields from a driven four-level atomic ensemble is investigated theoretically by using the state vector method. The violation of Cauchy-Schwarz inequality, which indicates the establishment of non-classical correlation between two emission fields, has been found. The effects of various decays and time delay on the correlation are discussed in detail, which are helpful in finding the ways to obtain high non-classical correlation. This technique for the generation of non-classical light is operable based on the current experimental technology and will lead to some potential applications in quantum information science.     

On the theory of light and atomic backscattering in the Bose-Einstein condensate of a dilute gas

A semiclassical theory of light scattering from a Bose-Einstein condensate of a dilute gas is developed. It is shown that the results of theoretical calculations are in qualitative agreement with the data obtained from recent experiments on the observation of atoms scattered in the backward direction with respect to the direction of a pump laser beam. It is demonstrated that there can arise a field that propagates in the backward direction and whose intensity exceeds the intensity of conventional Rayleigh scattering.     

Rotational tunneling dynamics of methyl groups inn-alkane host lattices: An optical investigation of the internal and external isotope effect

We exploited the slow relaxation of methyl group rotational tunneling states to perform optical hole burning inn-alkane crystals. The dye probe used was dimethyl-s-tetrazine and its perdeuterated derivative. We investigatedn-octane, perdeuteratedn-octane andn-hexane as host crystals. By comparing the experimentally observed hole-antihole splitting of the protonated and perdeuterated dye probe, all parameters, i.e. the tunneling splitting in the ground-and in the electronically excited state as well as the respective heights of the potential can be determined, assuming a threefold rotational symmetry axis. We found that matrix deuteration has a severe influence on the potential heights, which increase by a factor of two. With these parameters determined, many features of the complex relaxation behavior of the tunneling states can be qualitatively understood: We found Raman-type conversion processes inn-octane-h ₁₈, Orbach-type processes inn-octane-d ₁₈ and inn-hexane we found, in addition, a relaxation regime governed by a Direct process. The experimental activation energies as well as the cross-over temperatures are in satisfying agreement with current theories.     

Controlled coupling of counterpropagating whispering-gallery modes by a single Rayleigh scatterer: a classical problem in a quantum optical light

We present experiments where a single subwavelength scatterer is used to examine and control the backscattering induced coupling between counterpropagating high-Q modes of a microsphere resonator. Our measurements reveal the standing wave character of the resulting symmetric and antisymmetric eigenmodes, their unbalanced intensity distributions, and the coherent nature of their coupling. We discuss our findings and the underlying classical physics in the framework common to quantum optics and provide a particularly intuitive explanation of the central processes.     

Gravitational instability of a dilute fully ionized gas in the presence of the Dufour effect

The gravitational instability of a fully ionized gas is analyzed within the framework of linear irreversible thermodynamics. In particular, the presence of a heat flux corresponding to generalized thermodynamic forces is shown to affect the properties of the dispersion relation governing the stability of this kind of system. The overall weight of the sole Dufour effect on the value of Jeans wavenumber is shown to be negligible.     

Macroscopic dynamics of a trapped Bose-Einstein condensate in the presence of 1D and 2D optical lattices

The hydrodynamic equations of superfluids for a weakly interacting Bose gas are generalized to include the effects of periodic optical potentials produced by stationary laser beams. The new equations are characterized by a renormalized interaction coupling constant and by an effective mass accounting for the inertia of the system along the laser direction. For large laser intensities the effective mass is directly related to the tunneling rate between two consecutive wells. The predictions for the frequencies of the collective modes of a condensate confined by a magnetic harmonic trap are discussed for both 1D and 2D optical lattices and compared with recent experimental data.     

Controlling the growth dynamics of carbon nanotips on substrates irradiated by a focused electron beam

The dynamics of nanopillar growth on a variety of substrates as a result of the deposition of hydrocarbon molecules by a sharply focused electron beam is studied. The growth rate is found to depend strongly on the substrate’s material, thickness, and surface condition. The results are explained through the dissociation of adsorbed molecules by scattered and secondary electrons far from the point of beam incidence, thereby reducing the flow of diffusion to a nanotip’s peak.     

三维光晶格中玻色凝聚气体基态波函数及干涉演化

基于Gross-Pitaevskii方程，运用有效化学势概念，研究了囚禁在组合势(由磁阱和三维光 晶格组成)中玻色凝聚气体在三维光晶格中的分布规律，并由此得到玻色凝聚气体的归 一化基态波函数.在取消组合势和仅取消光晶格而保留磁阱的两种情况下，运用传播子方 法求解出玻色凝聚气体密度分布的解析表达式.取消组合势后，理论计算所得到的玻色凝聚 气体聚随时间的演化规律与Greiner等的实验结果相一致.仅取消光晶格而保留磁阱时，研 究表明玻色凝聚气体的干涉模式呈现周期性的振荡行为.此外，在磁阱为各向异性的情况下 ， 关键词： 玻色凝聚气体 磁阱 光晶格 干涉模式     

Simulating cyclotron-Bloch dynamics of a charged particle in a 2D lattice by means of cold atoms in driven quasi-1D optical lattices

Quantum dynamics of a charged particle in a two-dimensional (2D) lattice subject to magnetic and electric fields is a rather complicated interplay between cyclotron oscillations (the case of vanishing electric field) and Bloch oscillations (zero magnetic field), details of which has not yet been completely understood. In the present work we suggest to study this problem by using cold atoms in optical lattices. We introduce a one-dimensional (1D) model which can be easily realized in laboratory experiments with quasi-1D optical lattices and show that this model captures many features of the cyclotron-Bloch dynamics of the quantum particle in 2D square lattices.     

Charged excitons at high magnetic fields: the effect of the surrounding electron gas

We study the photoluminescence (PL) spectrum of a two-dimensional electron system at the high magnetic field limit, where all electrons reside at the lowest Landau level (ν<2). Using a gated structure we tune the electron density from the dilute limit to a dense electron gas, and follow the changes in the emission spectrum. We find that the spectrum at the dilute limit consists of two bound triplets, whose behavior is consistent with that of the dark and bright triplets. We show that the spectrum undergoes critical changes at ν=1/3, from an isolated charged exciton-like spectrum at ν<1/3, to a spectrum that reflects the interactions with the surrounding electrons above this filling factor. This behavior is found to be robust, independent of the electron density and magnetic field. We compare our observations with other recent low temperature PL measurements of a two-dimensional electron gas at high magnetic field and find good agreement and consistency.     

Formation of optical fields of stimulated Raman scattering with a resolution beyond the Abbe diffraction limit by spherical microlens cavities with whispering gallery modes: Near-field approximation

We consider a significant lowering of the threshold of stimulated Raman scattering in solid fused silica spherical microlenses cavities that is caused by an increase in the integral overlap factor of whispering gallery modes. The structure of focal regions of a microlens is shown to have the shape of honeycombs, forming a photonic crystal or a photonic nanojet. We show that, at comparatively small numerical apertures NA = 0.7–0.8, which correspond to hemispherical microlenses, a spherical microlens cavity exhibits the possibility of focusing laser radiation beyond the Abbe diffraction limit. This enables the possibility of wide practical applications of microspheres as a focusing element the resolving power of which exceeds the Abbe diffraction limit in the near field. The whispering-gallery-mode spherical microlens cavity makes it possible to perform laser generation with a duration of a coherent pulse in the subfemtosecond range and to form a subwavelength focal region of the near field. This ensures the possibility of detecting single molecules of a substance in the subwavelength range in the near field and can be used to increase the sensitivity of intracavity spectroscopy methods and as microlasers for excitation of molecules in metal molecular nanoswitches and semiconductor heterostructures. From an array of microlens cavities, metamaterials with a negative refractive index can be formed.     

The influence of higher spatial harmonics of atomic polarization on the saturated absorption resonance upon excitation of open dipole transitions by a field of counterpropagating waves

The effect of a double structure of saturated absorption resonance in the field of counterpropagating light waves interacting with an atomic gas is studied. The experimental observation of this effect was first reported in 2011 in a work by our colleagues at the P.N. Lebedev Physical Institute of the Russian Academy of Sciences (Laboratory of Frequency Standards). The essence of the effect lies in the fact that, on exciting an open dipole transition, another, narrower, resonance of an opposite sign can be observed at the center of the ordinary saturated absorption resonance. A theoretical analysis of this effect has also been performed in this work in terms of a simple spectroscopic model of an atom with two nondegenerate energy levels without taking into account higher spatial harmonics of atomic polarization and polarizations of light waves (scalar model). The present work is devoted to the development of a theory of the formation of a central narrow resonance for the example of a real F _g = 1 → F _e = 1 atomic transition and to the study of its main characteristics (amplitude, width, contrast, and amplitude-to-width ratio). In addition, the theoretical results obtained without taking into account the influence of higher spatial harmonics and with inclusion of the influence of first higher harmonics are compared. This comparison shows that their influence on the parameters of the new nonlinear resonance is strong even in moderately intense light fields (R ~ γ, where R is the Rabi frequency). The results of this study can be of interest for quantum metrology, as well as for many experiments in which the laser-radiation frequency is stabilized by the saturated absorption resonance on open dipole transitions in atoms and molecules.     

The effect of dilute nitrogen on nonlinear optical properties of the InGaAsN/GaAs single quantum wells

Employing the extended dynamical mean field theory (EDMFT) and the quantum Monte Carlo (QMC) method, we investigate the effect of the spatial fluctuations in the two-band Hubbard model with anisotropic bandwidth in the vicinity of the Mott metal-insulator transition. At half filling, we demonstrate that while the inclusion of the non-local spin-spin interaction amounts to enhancing the correlation and suppressing the metallic character, the orbitally selective Mott transition (OSMT) remains stable for various strengths of the non-local correlation. The same is true when the system is doped away from half filling. The OSMT phase is evidenced at low dopant concentration and the simultaneous metallic phase emerges at overdoped regime. From the analysis of the self energy, it follows that the nature of the metallic phase upon doping violates the Fermi liquid character and persists at considerably large doping. Our theory also offers a new perspective for the investigation of the non-local fluctuation in the multi-orbital system within the single-site scheme.