Search

The derivations of several conservation laws of the generalized nonlocal nonlinear Schrodinger equation are pre- sented. These invariants are the number of particles, the momentum, the angular momentum and the Hamiltonian in the quantum mechanical analogy. The Lagrangian is also presented.

We propose an approach to cool a mechanical resonator (MR) via quantum interference in a triple quantum dot (TQD) capacitively coupled to the MR. The TQD connected to three electrodes is an electronic analog of a three-level atom in $\Lambda$ configuration. The electrons can tunnel from the left electrode into one of the two dots with lower-energy states, but can only tunnel out from the higher-energy state at the third dot to the right electrode. When the two lower-energy states are tuned to be degenerate, an electron in the TQD can be trapped in a superposition of the degenerate states called the dark state. This effect is caused by the destructive quantum interference between tunneling from the two lower-energy states to the higher-energy state. Under this condition, an electron in the dark state readily absorbs an energy quantum from the MR. Repeating this process, the MR can be cooled to its ground state. Moreover, we propose a scheme for verifying the cooling result by measuring the current spectrum of a charge detector adjacent to a double quantum dot coupled to the MR., Comment: 12 pages, 5 figures

We study shot noise in tunneling current through a double quantum dot connected to two electric leads. We derive two master equations in the occupation-state basis and the eigenstate basis to describe the electron dynamics. The approach based on the occupation-state basis, despite widely used in many previous studies, is valid only when the interdot coupling strength is much smaller than the energy difference between the two dots. In contrast, the calculations using the eigenstate basis are valid for an arbitrary interdot coupling. We show that the master equation in the occupation-state basis includes only the low-order terms with respect to the interdot coupling compared with the more accurate master equation in the eigenstate basis. Using realistic model parameters, we demonstrate that the predicted currents and shot-noise properties from the two approaches are significantly different when the interdot coupling is not small. Furthermore, properties of the shot noise predicted using the eigenstate basis successfully reproduce qualitative features found in a recent experiment., Comment: 13 pages, 5 figures

The propagation and interaction properties of optical vortex solitons in a self-defocusing Kerr-type nonlocal medium are investigated by the numerical simulation method. It is indicated that the singly charged vortices are stable and the multicharged vortices are topologically unstable in both the nonlocal and local cases. And in the nonlocal and local cases the point vortices model is applicable for describing the interactions of vortices provided that the interval distances between vortices are much larger than the size of the core of the vortices. However, vortices interact differently in short distance, depending on the nonlocality, and the larger the characteristic nonlocal respond length, the larger the rotating period of two singly charged vortices.

The interaction between photovoltaic spatial solitons with difference wavelengths in photovoltaic-photorefractive crystals is investigated by numerical method. Our numerical study indicates that the interaction between these solitons is inelastic, and these solitons keep their shapes only within some propagation distance. Besides the attraction with each other, the energy of soliton would be coupled from one waveguide to other waveguide during propagation.

An approximate method is presented to calculate the full width at half maximum(F WHM) of photovoltaic(PV) spatial solitons(PVSSs) with twowavelengths component . An advanced numerical analysis i ndicates that two coaxial hyperbolic secant beams, provided that they satisfy th e functional relations of FWHM with amplitudes of this type of PVSS, will be ver y close to solitons when they propagate in PV crystals. Besides, this type of PV S S tends to be stable against small axial perturbations and small refractive inde x perturbations due to variations of temperature of the crystal. However, if the pro files of intensity of two coaxial signal beams with different wavelengths diff e r mildly from those of PVSS, the two beams will tend to experience cycles of co mpression and expansion; and if the profiles of intensity of the signal beams di ffer significantly from those of PVSS, these two signal beams will diffuse endle ssly.

The parallel interaction between two photovoltaic spatial solitons of dark and dark as well as dark and bright with different wavelengths is investigated by numerical method. Our numerical study indicates that the dark solitons can both remain as quasi soliton form in certain distance while they propagate coaxially. H owever,they attract each other while closely overlapping. And they have a conver gent effect on each other at the slowly varying region of optical field while in larger separations. For the case of interaction between dark and bright, the br igh t one may experience compression, expansion or energy transfer depending on thei r mutual separation.The physical interpretation of this solitons interaction is also given in terms of the refractive index waveguide they jointly induce.

The photovoltaic effect of a background beam do not affect the spatial-charge field in a photovoltaic crystal with a constant external applied field, but has an effect on the current density in the crystal.If the crystal is connected with an external circuit which includes a resistor and a constant voltage source, the photovoltaic effect of the background beam will affect the full width at half maximum of the solitons, even switch the bright solitons, to the dark solitons, or vice versa.

Dielectric behavior and optical absorption of quartz glasses before and after irradiating were investigated. Experimental results demonstrate that complex dielectric function of quartz glasses is changed by the irradiation. Its magnitude is decreased by the irradiation. In addition, the change in the dielectric function does not relate to the hydroxyl group in quartz glasses. Experiments also show that dielectric function is relating to the color centers in quartz glasses. Contribution of color center to dielectric function is dependent on its sort and amount in quartz glasses. Dielectric constant decreases with increasing the density of color center