Optically induced mechanical interaction between semiconductor quantum dots under an electronic resonance condition

Assuming an electronic resonance condition, we study the shape-dependence of the radiation force (RF) on a semiconductor quantum dot (QD) floating in medium and the optically induced mechanical interaction (OIMI) between two QDs with Maxwell stress tensor (MST) method, where the response fields are calculated by the improved discrete dipole approximation (DDA). Main results are as follows: (1) Properties of the RF on an isolated QD drastically change due to its shape and polarization of an incident light, which can be used for shape-selective manipulation. (2) Anomalous OIMI between two QDs arises depending on the spatial structures of internal fields, which results from the interaction between polarizations in respective QDs when they are near each other.     

改进型COBRA透镜天线的设计

 设计了X波段COBRA透镜型天线,利用电磁波在不同介质传播速度的差异,通过放置于圆锥喇叭口径处不同厚度的介质透镜改变TM₀₁模不同扇区的相位,从而改变TM₀₁模在普通喇叭口径处的轴对称分布,将轴对称的口径场分布转换为线对称,进而实现线极化或圆极化的轴向辐射。通过添加匹配介质,减小介质对微波的反射和驻波特性的影响;延伸喇叭到透镜边缘,使移相过程在波导内完成,有效地控制了电磁场模式。天线增益在中心工作频率为9.3 GHz时为19 dB,口径效率25%,辐射效率大于90%,反射系数小于1.3,轴比小于2 dB, 3 dB相对带宽大于30%,几乎可以覆盖整个X波段。     

Similarity-Projection Structures: The Logical Geometry of Quantum Physics

Similarity-Projection structures abstract the numerical properties of real scalar product of rays and projections in Hilbert spaces to provide a more general framework for Quantum Physics. They are characterized by properties that possess direct physical meaning. They provide a formal framework that subsumes both classical Boolean logic concerned with sets and subsets and quantum logic concerned with Hilbert space, closed subspaces and projections. They shed light on the role of the phase factors that are central to Quantum Physics. The generalization of the notion of a self-adjoint operator to SP-structures provides a novel notion that is free of linear algebra. This work was partially supported by the Jean and Helene Alfassa fund for research in Artificial Intelligence.     

Optimally chosen Nakajima–Zwanzig master equation for mean field approximation

We define an ensemble of projection operators, each of which has an exact associated Nakajima–Zwanzig master equation for quantum open system evolution. A mean field approximation for the memory kernels is introduced that yields a completely determined inhomogeneous master equation for every projection operator. A specific projection operator is then chosen so that the master equation optimally matches an abstract mathematical form which preserves positivity, complete positivity, and correctly equilibrates. We study a nitrogen vacancy center in diamond interacting with ¹³C impurities to illustrate the method.     

The randomly fluctuating impurity strength initiated excitation in doped quantum dots

We investigate the excitation behavior of a repulsive impurity doped quantum dot under the influence of randomly fluctuating dopant potential. We have considered Gaussian impurity centers doped at different locations. The investigation reveals the interplay between dopant location and dopant’s spatial stretch in modulating the excitation pattern. Maximization in the excitation rate has been observed as a function of fluctuating dopant strength owing to the conflict between opposing influences that promote and hinder excitation.     

Size-dependent visible photoluminescence from ZnO nanoparticles prepared via SiO2 network

This study reports a simple method for the synthesis of different size of wurtzite ZnO nanoparticles in assistance of tetraethyl orthosilicate (TEOS). With the increase of the amount of TEOS added, the average size of ZnO nanoparticles was found decreased from ∼14.6 to ∼1.9 nm by characterization of X-ray diffraction (XRD) and high-resolution electron microscopy (HRTEM). The growth of ZnO nanoparticles is proposed to be controlled by the density of the SiO₂ chain mesh which is determined by TEOS amount in precursor. Ultraviolet–visible (UV–VIS) absorption and photoluminescence (PL) spectra show both shift to higher energy in cut-off edge and in visible emission bands respectively. The electron transition process in the mechanism of the visible emission shift was described and related to quantum size effect in ZnO nanoparticles.     

Long-time fidelity and chaos for a kicked nonlinear oscillator system

We deal with a system comprising a nonlinear (Kerr-like) oscillator excited by a series of ultra-short external pulses. We introduce the fidelity-based entropic parameter that can be used as an indicator of quantum chaos. Moreover, we propose to use the fidelity-like parameter comprising the information about the mean number of photons in the system. We shall concentrate on the long-time behaviour of the parameters discussed, showing that for deep chaos cases the quantum fidelities behave chaotically in the classical sense despite their strictly quantum character.     

Versatile wideband balanced detector for quantum optical homodyne tomography

We present a comprehensive theory and an easy to follow method for the design and construction of a wideband homodyne detector for time-domain quantum measurements. We show how one can evaluate the performance of a detector in a specific time-domain experiment based on the electronic spectral characteristic of that detector. We then present and characterize a high-performance detector constructed using inexpensive, commercially available components such as low-noise high-speed operational amplifiers and high-bandwidth photodiodes. Our detector shows linear behavior up to a level of over 13 dB clearance between shot noise and electronic noise, in the range from DC to 100 MHz. The detector can be used for measuring quantum optical field quadratures both in the continuous-wave and pulsed regimes with standard commercial mode-locked lasers.     

Sustained turbulence in the three-dimensional Gross-Pitaevskii model

We study the three-dimensional forced-dissipated Gross-Pitaevskii equation. We force at relatively low wave numbers, expecting to observe a direct energy cascade and a consequent power-law spectrum of the form k^−α. Our numerical results show that the exponent α strongly depends on how the inverse particle cascade is attenuated at ks lower than the forcing wave-number. If the inverse cascade is arrested by a friction at low ks, we observe an exponent which is in good agreement with the weak wave turbulence prediction k⁻¹. For a hypo-viscosity, a k⁻² spectrum is observed which we explain using a critical balance argument. In simulations without any low k dissipation, a condensate at k=0 is growing and the system goes through a strongly turbulent transition from a 4-wave to a 3-wave weak turbulence acoustic regime with evidence of k^−3/2 Zakharov-Sagdeev spectrum. In this regime, we also observe a spectrum for the incompressible kinetic energy which formally resembles the Kolmogorov k^−5/3, but whose correct explanation should be in terms of the Kelvin wave turbulence. The probability density functions for the velocities and the densities are also discussed.