Action–angle variables,ladder operators and coherent states

This Letter is devoted to the building of coherent states from arguments based on classical action–angle variables. First, we show how these classical variables are associated to an algebraic structure in terms of Poisson brackets. In the quantum context these considerations are implemented by ladder type operators and a structure known as spectrum generating algebra. All this allows to generate coherent states and thereby the correspondence of classical–quantum properties by means of the aforementioned underlying structure. This approach is illustrated with the example of the one-dimensional Pöschl–Teller potential system.     

Coherent phonon dynamics in short-period InAs/GaSb superlattices

We have performed ultrafast pump-probe spectroscopy studies on a series of InAs/GaSb-based short-period superlattice (SL) samples with periods ranging from 46 Å to 71 Å. We observe two types of oscillations in the differential reflectivity with fast (∼$\sim$1–2 ps) and slow (∼$\sim$24 ps) periods. The period of the fast oscillations changes with the SL period and can be explained as coherent acoustic phonons generated from carriers photoexcited within the SL. This mode provides an alternative method for determining the SL period. The period of the slow mode depends on the wavelength of the probe pulse and can be understood as a propagating coherent phonon wavepacket modulating the reflectivity of the probe pulse as it travels from the surface into the sample.     

Dynamic sampling algorithms for multi-stage stochastic programs with risk aversion

We consider the incorporation of a time-consistent coherent risk measure into a multi-stage stochastic programming model, so that the model can be solved using a SDDP-type algorithm. We describe the implementation of this algorithm, and study the solutions it gives for an application of hydro-thermal scheduling in the New Zealand electricity system. The performance of policies using this risk measure at different levels of risk aversion is compared with the risk-neutral policy.     

Self-diffusion in liquid lithium from coherent quasielastic neutron scattering

Using the method of quasielastic coherent neutron scattering by liquid lithium, the temperature dependence of self-diffusion coefficient is investigated and compared with analogous data extracted by the incoherent scattering method.     

激光微多普勒探测系统中降低相位噪音影响的方法研究

相干微多普勒激光雷达具有探测灵敏度高、探测信息量大等特点,特别适合于动目标探测、目标特征识别等应用.本文从线宽和探测距离两个方面讨论了模场相位随机起伏（相位噪音）对于测速准确度的影响,实验证实了相位噪音对激光微多普勒探测的影响,并探索出解决上述问题的方法——光纤补偿法.实验中,以输出波长为1.064 μm单块非平面环形腔激光器为光源,利用光纤补偿方法,并结合时频变换的算法,用外差探测的方式成功观测到了微多普勒频移,在传输距离为11 km时,系统最低探测速度达到了0.5 mm/s,速度分辨率达到了mm/s量级,频率分辨率达到了kHz量级,为微多普勒激光雷达的实际应用奠定了良好的实验基础.     

The geometric phase of a two-level atom in a narrow-bandwidth squeezed vacuum

In this paper, we derive the time dependent solution of the effective master equation for the reduced density matrix operator of a two level atom driven by a coherent laser field and damped by a finite bandwidth squeezed vacuum. The results show that the initial state setting, detuning parameter and Rabi frequency play important roles in the evolution of the system dynamics and geometric phase. We present a useful way for controlling the geometric phase variation for the system under consideration.     

Ballistic electron transport in wrinkled superlattices

Inspired by the problem of elastic wave scattering on wrinkled interfaces, we studied the scattering of ballistic electrons on a wrinkled potential energy region. The electron transmission coefficient depends on both wrinkle amplitude and periodicity, having different behaviors for positive and negative scattering potential energies. For scattering on potential barriers, minibands appear in the electron transmission, as in superlattices, whereas for scattering on periodic potential wells the transmission coefficient has a more complex form. Besides suggesting that tuning of electron transmission is possible by modifying the scattering potential via voltages on wrinkled gate electrodes, our results emphasize the analogies between ballistic electrons and elastic waves even in scattering problems on non-typical configurations.     

Intrinsic anisotropy of the effective acoustic properties in metafluids made of two-dimensional cylinder arrays

Within a unified theoretical framework, we extract the omnidirectional effective acoustic parameters for the metafluid consisting of isotropic fluid cylinders embedded in an isotropic fluid background. Besides the analytical formulas for the effective parameters reported previously, i.e., the bulk modulus and the mass density perpendicular to the cylinders, we also derive a simple expression for the effective mass density parallel to the cylinders. As expected, these two effective mass densities are not identical and constitute an anisotropic density tensor. Such intrinsic anisotropy can be engineered much stronger than the pure in-plane anisotropy induced by either anisotropic lattices or anisotropic scatterers.     

干涉型复合腔激光束相干合成中分束器的相移特性研究

分析了采用分束器构建干涉型复合腔进行激光束相干合成的过程与原理.利用分束器的特征矩阵研究了分束时产生的反射与透射相移,得到了两束相干光经过分束器分束后进行相干叠加时相移满足的普适关系,从相移的角度解释了分束器一侧发生相长干涉时另一侧必然发生相消干涉这一现象.比较了分束器与光纤耦合器在激光束相干合成应用中的一些特性,并验证了所得相移关系式的正确性.