Output Properties of Non-degenerate Parametric Amplifiers with Non-homogeneous Linear Losses

Abstract

The noise properties of non-degenerate parametric amplifiers with absorption losses which are different for the two beams are analysed by means of a semiclassical approach which enables the direct derivation of the Langevin equations for the optical fields from the quantum Heisenberg equations. Several statistical quantities are calculated and the implications of the present results for sub shot-noise absorption measurements are discussed finally.     

Quantum Statistical Properties of Coupled Nonlinear Oscillators with Losses

Abstract

The statistical properties of two coupled nonlinear oscillators including losses are discussed using the statistics for the generalized superposition of coherent fields and quantum noise. Exact and approximate formulae for squeezing of vacuum fluctuations are derived. The photon statistics are shown to be Poissonian from the nonlinear dynamics of the lossless case. Non-classical behaviour is degraded by noise.     

Quantum Degenerate Fermi Gases of Ytterbium Atoms

We performed evaporative cooling for dilute gases of ytterbium (Yb) isotopes in a crossed optical dipole trap and successfully cooled two fermionic and two bosonic species down to quantum degenerate regime, following the previous realization of Bose-Einstein condensation (BEC) in ¹⁷⁴Yb. The elastic collision rate of fermionic ¹⁷³Yb atoms with 6 spin components was found to be large enough to carry out efficient evaporation, which enables us to cool the atoms down to 0.6 T _F , where T _F is the Fermi temperature. In this regime, a plunge of evaporation efficiency was observed as an effect of the Fermi degeneracy. The other fermionic isotope ¹⁷¹Yb was cooled down to the temperature below T _F by sympathetic cooling with bosonic ¹⁷⁴Yb atoms. The sympathetic cooling technique has also been applied to ¹⁷⁴Yb-¹⁷⁶Yb Bose-Bose mixture. We have observed almost pure BEC of ¹⁷⁴Yb and the bimodal distribution of ¹⁷⁶Yb, showing the formation of BEC-BEC mixture. Moreover, we performed evaporative cooling of ¹⁷⁰Yb atoms and realized the BEC.     

Quantum Statistical Properties of Photon and Phonon Fields in Brillouin Scattering with Intense Pumping

The quantum statistical properties of Brillouin scattering of intense laser light are derived including the coupling of Stokes, anti-Stokes and phonon modes, if the anti-Stokes interaction prevails. Making use of the coherent-state technique, the Heisenberg equations of this process are solved neglecting the loss mechanism, and the normal quantum characteristic function and the normal generating function are derived. The time dependences of the photon distribution and its factorial moments are demonstrated if the phonon, Stokes and anti-Stokes modes are initially in a coherent state and periodical anti-bunching of the field is found when the phases of the incident fields fulfil certain phase conditions; the field can also return to the coherent state again.     

Photon Statistics of Atomic Fluorescence Near a Phase-conjugate Mirror or a Degenerate Parametric Amplifier

Abstract

We have studied the modification of the photon statistics of the resonance fluorescence of a coherently driven two-state atom due to the presence of a phase-conjugate mirror (PCM) or a degenerate parametric amplifier (DPA). In both cases, we give explicit expressions for the n-fold intensity correlation function. We find that the photon statistics depends on the relative phase of the PCM or DPA and the driving field. The non-classical properties of the photon statistics can be enhanced because of the presence of the PCM or of the DPA, when the decay of the coherences is obstructed.     

Properties of Metastable Quantum Solids

We consider the properties of quantum solids at pressures below the pressure range in which the solid is the stable phase. We estimate the spinodal pressure and determine how this pressure varies as a function of the de Boer parameter.     

关于量子概率论的若干研究

本文证明了以下结论:算子关于一秩投影的绝对方差的绝对值的上确界等于这个算子到所有数乘算子的距离的平方;一个密度算子是忠实的当且仅当它是单射;算子列在密度算子ρ的值域的闭包上的强收敛性蕴含它关于ρ的a.s.收敛性;如果算子列关于每个密度算子是a.s.收敛的,那么它一定是强收敛的;算子列{An}强收敛于A当且仅当它是一致有界的且关于某个忠实的密度算子ρa.s.收敛于A。     

Phase States and Their Statistical Properties

Abstract

We study the statistical properties of radiation in the single-mode phase states by evaluating the expression for the photon-counting distribution and its factorial moments. A detailed comparison has been made of the properties of phase states with those of coherent and chaotic states.     

Statistical Analysis and Robust Optimization of Forming Processes and Forming-to-Crash Process Chains

In this paper, a novel strategy for statistical analysis and multi-objective robust design-parameter optimization of forming processes as well as forming-to-crash process chains is discussed and results presented for a ZStE340 metal blank of a B-pillar. The strategy comprises both physical experiments and numerical simulation and is built upon a novel material and damage model as well as several software tools which allow for an efficient sensitivity, stability and robustness analysis, even for simulation results on highly resolved grids.     

Ground-State Properties of Electron-Electron Quantum Bilayers

The ground-state behavior of electron-electron quantum bilayer systems within the neutralizing background and zero magnetic field is studied by including unequal density of layers. The quantum self-consistent mean-field approximation of Singwi, Tosi, Land and Sjölander (qSTLS) is used to study the intra- and inter layer properties, such as the static pair-correlation functions, the static structure factors, the static density susceptibility and the static local-field correction factors over a wide range of layer density parameter r _s?? and layer spacing d. We find that the inclusion of unequal density brings a phase transition from charge density wave (CDW) to coupled Wigner crystal (WC) ground state at the close proximity of the layers. We also find that inclusion of unequal density markedly reduce critical r _s?? for the onset of Wigner crystallization. The results are compared with recent findings of the equal density effects in electron-electron quantum bilayer systems.     

Quantum Statistics of the Optical Parametric Process for Arbitrary Initial States

Abstract

Photon statistics and non-classical behaviour of light produced in the optical parametric process are studied in the approximation of small fluctuations around a stationary point. The depletion of the pump mode is included. An initial generalized superposition of a coherent state and noise as well as the influence of reservoir noise and internal losses are considered.     

Properties of the Optical Quantum Amplifier

The properties of a linear optical amplifier or attenuator in which the input light is coupled to a collection of non-saturable atoms are considered. The photon-number factorial moments and probability distribution of the amplifier output are derived for arbitrary input statistics. Relations are obtained between the output and input variances in photon number, phase-angle cosine, and electric-field magnitude. The effects of amplification and attenuation on signal-to-noise ratio are obtained for both direct and homodyne detection. Particular attention is paid to the extents to which the non-classical properties of photon antibunching and squeezing are preserved by amplification and attenuation. It is found that both properties can at best survive only twofold intensity amplification.     

Measurements of Second-Order Properties of Point Processes

The second-order statistical properties of point processes (PPs) are described by the coincidence function which can be measured by a coincidence device, but such measurements are long and complicated. We propose another method of measurement, and we analyze its performances. The starting point is that the coincidence function can be deduced from the probability density functions of the life times (the distances between points) of the process. The idea is to transform the PP into a positive signal whose values are these distances. From an appropriate processing of this signal, we deduce the coincidence function. For the validation of the method, we use PPs for which the coincidence function is known. The agreement between theory and experiment is, in general, excellent. Finally, the method is applied to measure the coincidence functions of some PPs for which no theoretical result is available.     

高荧光量子产率的二硫化钼量子点制备及荧光性能研究

二硫化钼量子点(MoS2 QDs)具有优良物理、化学等特性,在催化、荧光成像和荧光传感及生物成像等方面具有潜在的应用前景,然而其制备方法及量子产率仍有改进空间.本工作以钼酸钠提供钼源,谷胱甘肽提供硫源,通过"自下而上"一步水热法制备MoS2 QDs,并以其荧光强度作为指标,采用单因素分析,优化MoS2 QDs制备条件中的钼源与硫源比例、pH值、反应时间、反应温度.结果表明,最佳钼源与硫源质量比例为1:3.5、最佳pH值为4?8之间、反应时间18 h、反应温度210℃.采用正交试验的方法,优化出MoS2 QDs的最佳制备条件为:反应时间30 h、反应温度220℃、钼源与硫源比例为1:3.5、pH值为3,荧光量子产率高达21％.所制备MoS2 QDs的粒径4.0±0.35 nm,且单分散,富含氨基和羧基官能团,紫外吸收峰336 nm;发射波长为424 nm;半峰宽79 nm.可为MoS2 QDs在高灵敏的离子、生物分子检测以及低毒的细胞成像打下基础.     

Estimating a Parametric Component Lifetime Distribution from a Collection of Superimposed Renewal Processes

Maintenance data can be used to make inferences about the lifetime distribution of system components. Typically, a fleet contains multiple systems. Within each system, there is a set of nominally identical replaceable components of particular interest (e.g., 2 automobile headlights, 8 dual in-line memory module (DIMM) modules in a computing server, 16 cylinders in a locomotive engine). For each component replacement event, there is system-level information that a component was replaced, but no information on which particular component was replaced. Thus, the observed data are a collection of superpositions of renewal processes (SRP), one for each system in the fleet. This article proposes a procedure for estimating the component lifetime distribution using the aggregated event data from a fleet of systems. We show how to compute the likelihood function for the collection of SRPs and provide suggestions for efficient computations. We compare performance of this incomplete-data maximum likelihood (ML) estimator with the complete-data ML estimator and study the performance of confidence interval methods for estimating quantiles of the lifetime distribution of the component. Supplementary materials for this article are available online.