依赖强度耦合的Λ型三能级Jaynes-Cummings模型的原子发射谱及腔场谱

在假设原子初始处于激发态并计入原子-场耦合强度依赖性的条件下,用本征函数法研究了Λ型三能级原子与单模腔场共振相互作用系统的原子发射谱和腔场谱。结果表明,基态能级裂距对谱结构有重要影响。发射谱和腔场谱的谱线随初场增强不发生合并现象,腔场谱对初场光子统计性质不敏感。     

依赖强度耦合的∧型三能级Jaynes-Cummings模型的原子发射谱及腔场谱

在假设原子初始处于激发态并计入原子-场耦合强度依赖性的条件下,用本征函数法研究了∧型三能级原子与单模腔场共振相互作用系统的原子发射谱和腔场谱.结果表明,基态能级裂距对谱结构有重要影响.发射谱和腔场谱的谱线随初场增强不发生合并现象,腔场谱对初场光子统计性质不敏感.     

微波调制的里德堡原子集体量子跳跃

对于一个三能级原子体系,原子的两个基态能级通过微波耦合起来,其中一个基态能级可被激发到里德堡态,从而可观察量子跳跃现象.本文采用量子轨线方法研究了微波调制的里德堡原子集体量子跳跃.研究结果表明,微波耦合基态能级可以提高光子关联,增强光子聚束效应,即使较少的原子中也可以观察到系统在高里德堡占据数态和低里德堡占据数态之间的切换.这一结果为将来进一步研究里德堡自旋晶格中的多体动力学提供了新思路.     

微波调制的里德堡原子集体量子跳跃

对于一个三能级原子体系,原子的两个基态能级通过微波耦合起来,其中一个基态能级可被激发到里德堡态,从而可观察量子跳跃现象.本文采用量子轨线方法研究了微波调制的里德堡原子集体量子跳跃.研究结果表明,微波耦合基态能级可以提高光子关联,增强光子聚束效应,即使较少的原子中也可以观察到系统在高里德堡占据数态和低里德堡占据数态之间的切换.这一结果为将来进一步研究里德堡自旋晶格中的多体动力学提供了新思路.     

双耦合场作用下的Mollow七峰谱

对双耦合A型三能级系统中Mollow谱线上叠加的新的透明和吸收特性进行了理论研究.若基态能级包括两条精细结构简并能级,强耦合场和探测场作用于激发态能级和第一条基态精细结构能级之间,另一个弱耦合场作用于激发态能级和第二条基态精细结构能级之间,则构成了双耦合A型三能级系统.通过调谐强耦合场的频率失谐量,探测吸收谱线中不仅得到了典型的Mollow三峰失谐谱,还出现了电磁诱导透明(EIT)和电磁诱导吸收(EIA)等新现象,形成了Mollow七峰谱.该文进一步分析了EIT和EIA的位置与耦合场参数之间的关系,并用缀饰态理论做出了解释.     

微波场对电磁诱导透明谱的局域调制

当用两个微波场作用到Λ型三能级原子的耦合跃迁的基态与另两个超精细能态构成的跃迁时,由微波场诱导产生的两个高对比度共振吸收线将单重电磁诱导透明谱分裂成三个透明窗口。通过调节微波场的强度或失谐量,可实现对原子透明谱进行局域调制。采用缀饰态理论对展示的物理现象进行了解释。这些研究对多通道光通信和原子的可控调制等方面有一定的作用。     

准Λ型四能级系统中的超窄谱线的研究

在一般Λ型三能级模型的基础上提出准Λ型四能级系统,并对准Λ型四能级模型的共振荧光谱作了详尽的研究.从上能级向两边下能级辐射的自发辐射谱中产生了三个超窄谱线,且在很大参数范围内光谱具有这一特性.三个超窄谱线的产生是和两个相干驱动场的Rabi频率密切相关,在较大的Rabi频率作用下谱线会变得更窄,而当只有一个驱动场作用时是不会产生谱线变窄效应的.能级间的碰撞弛豫和非相干激发严重地破坏了谱线变窄.这种超窄谱线效应是多通道量子干涉的结果 关键词： 准Λ型四能级系统 超窄谱线 多通道量子干涉     

激光场线宽对四能级原子系统相干效应的影响

采用密度矩阵方程,在引入激光场线宽的条件下,计算了N型四能级原子系统中介质对探测场的吸收。结果表明:耦合场线宽的引入,消弱了四能级原子相干,对抑制吸收有增强作用,对增强吸收有抑制作用,即耦合场线宽的引入导致了退相干。控制场线宽的引入,在电磁感应透明中削弱了四能级原子相干性,降低了共振吸收,增强了光透明;在电磁感应吸收中,控制场线宽的增加使谱线中心两侧的吸收增强,削弱了谱线中心的吸收增强,从而使四能级系统的电磁感应吸收转换为电磁感应透明。     

利用微波场抑制电磁感应透明的功率展宽

电磁感应透明的重要参量之一是透明窗口的光谱线宽。在Λ-型三能级原子系统中,电磁感应透明的光谱线宽由两低能级间的相干失相速率决定,若两低能级同属于原子基态的精细结构,则电磁感应透明窗口的极限线宽很窄。但较强的耦合场作用往往会导致电磁感应透明窗口的功率展宽,而减弱耦合场又会影响电磁感应透明的对比度和深度。为此,通过引入微波控制场共振作用于基态精细能级间构成三场作用下的准Λ-型四能级系统,利用微波控制场来抑制耦合场所引起的电磁感应透明窗口的功率展宽。结果表明,引入微波控制场不仅得到了双窗口电磁感应透明,而且在保持较好对比度的条件下,使得电磁感应透明的光谱线宽明显小于不加微波场的情况。     

双波场共振泵浦的四能级原子系统

本文运用Dressed原子态方法;把四能级原子与两个激光场和一个探测场的相互作用转化为四能级原子与一个弱探测吸收场的相互作用,然后采用微扰理论求解Dressed原子表象中的密度矩阵方程,得出吸收谱的解析表达式,并详细讨论了吸收谱的各种持性.最后,导出了由外场感应的能级间的电偶极矩表达式,并找出了吸收谱与它的关系.     

Formation of a bistructure of a solid in a computer experiment

Molecular-dynamics was used to investigate the structural changes occurring in a three-dimensional solid when the solid is transferred from an amorphous into a crystalline state. Crystal cells of a new type — pentadecahedrons with five square lateral faces and ten regular triangular faces at the vertices of a cell — were found for the first time in a computer experiment. It is shown that a bistructure consisting of crystal cells of different types, including cells with five-fold symmetry axes, are stable in the solid. Fiz. Tverd. Tela (St. Petersburg) 40, 1919–1924 (October 1998)     

Instability of a flat horizontal interface between a thin layer of a ferrofluid and a thin layer of a nonmagnetic liquid in the presence of a vertical magnetic field

An asymptotic analysis of the equations and boundary conditions of fluid dynamics is performed, and a nonlinear model is constructed for the onset of the development of Rosensweig instability in a thin horizontal ferrofluid layer at rest covered with a thin layer of a lighter nonmagnetic liquid. The surface of a nonmagnetized slab is the lower boundary of the ferrofluid, and the interface with a gas is the upper boundary of the nonmagnetic liquid. The pressure in the gas is constant. The instability being considered arises upon the application of a rather strong uniform vertical magnetic field. The proposed model involves five dimensionless parameters. The critical magnetization of the initial ferrofluid layer with a flat upper boundary and the threshold wave number are found. The effect of the governing parameters on the instability region and on the wavelength of the fastest growing mode is studied in the linear formulation of the problem.     

Design of a suspension of a training sulky

A design study based on a modelling approach was used to optimise the characteristics of a new concept of suspension for training sulkies. The numerical model of sulky including the suspension and, in a second stage, a mechanical model of driver, allowed the definition of technical specifications. They were used to manufacture a prototype of suspension mounted on a current production model of sulky. The prototype of suspension was then tested in the lab and in a racecourse in real conditions of use.The resulting vibration exposure was assessed from vibration measurements. It was slightly lower than the limit value enacted in the European Vibration directive (1.15 m s²), but drastically reduced in comparison with the exposure measured on the original sulky (2.56 m s²). The prototype and moreover the design procedure is currently in a transfer process towards sulky manufacturers.     

Behavior of a free surface of a magnetic fluid containing a magnetizable cylinder

The deformation of the free surface of a magnetic fluid containing a cylinder made of a magnetizable material subjected to a uniform applied magnetic field is analyzed. The statics and dynamics of a magnetic fluid free surface is studied theoretically and experimentally. A discontinuous (jump-like) change of the surface shape is shown to occur when the applied magnetic field gradually increases or decreases. If the applied magnetic field increases and then decreases, a hysteresis of the shape is observed.     

Inferring a Property of a Large System from a Small Number of Samples

Inferring the value of a property of a large stochastic system is a difficult task when the number of samples is insufficient to reliably estimate the probability distribution. The Bayesian estimator of the property of interest requires the knowledge of the prior distribution, and in many situations, it is not clear which prior should be used. Several estimators have been developed so far in which the proposed prior us individually tailored for each property of interest; such is the case, for example, for the entropy, the amount of mutual information, or the correlation between pairs of variables. In this paper, we propose a general framework to select priors that is valid for arbitrary properties. We first demonstrate that only certain aspects of the prior distribution actually affect the inference process. We then expand the sought prior as a linear combination of a one-dimensional family of indexed priors, each of which is obtained through a maximum entropy approach with constrained mean values of the property under study. In many cases of interest, only one or very few components of the expansion turn out to contribute to the Bayesian estimator, so it is often valid to only keep a single component. The relevant component is selected by the data, so no handcrafted priors are required. We test the performance of this approximation with a few paradigmatic examples and show that it performs well in comparison to the ad-hoc methods previously proposed in the literature. Our method highlights the connection between Bayesian inference and equilibrium statistical mechanics, since the most relevant component of the expansion can be argued to be that with the right temperature.