Coulomb drag in double quantum wells with a perpendicular magnetic field

Momentum transfer due to electron-electron interaction (Coulomb drag) between two quantum wells, separated by a distance $d$, in the presence of a perpendicular magnetic field, is studied at low temperatures. We find besides the well known Shubnikov-de Haas oscillations, which also appear in the drag effect, the momentum transfer is markedly enhanced by the magnetic field.Comment: 8 pages, Revtex, 4 Postscript figures are available upon request, Accepted by Mod. Phys. Lett.

Gluon GPDs and Exclusive Photoproduction of a Quarkonium in Forward Region

Forward photoproduction of $J/\psi$ can be used to extract Generalized Parton Distributions(GPD's) of gluons. We analyze the process at twist-3 level and study relevant classifications of twist-3 gluon GPD's. At leading power or twist-2 level the produced $J/\psi$ is transversely polarized. We find that at twist-3 the produced $J/\psi$ is longitudinally polarized. Our study shows that in high energy limit the twist-3 amplitude is only suppressed by the inverse power of the heavy quark mass relatively to the twist-2 amplitude. This indicates that the power correction to the cross-section of unpolarized $J/\psi$ can have a sizeable effect. We have also derived the amplitude of the production of $h_c$ at twist-3, but the result contains end-point singularities. The production of other quarkonia has been briefly discussed.Comment: Discussions of results are adde

Shot noise of inelastic tunneling through quantum dot systems

We present a theoretical analysis of the effect of inelastic electron scattering on current and its fluctuations in a mesoscopic quantum dot (QD) connected to two leads, based on a recently developed nonperturbative technique involving the approximate mapping of the many-body electron-phonon coupling problem onto a multichannel single-electron scattering problem. In this, we apply the B\"uttiker scattering theory of shot noise for a two-terminal mesoscopic device to the multichannel case with differing weight factors and examine zero-frequency shot noise for two special cases: (i) a single-molecule QD and (ii) coupled semiconductor QDs. The nonequilibrium Green's function method facilitates calculation of single-electron transmission and reflection amplitudes for inelastic processes under nonequilibrium conditions in the mapping model. For the single-molecule QD we find that, in the presence of the electron-phonon interaction, both differential conductance and differential shot noise display additional peaks as bias-voltage increases due to phonon-assisted processes. In the case of coupled QDs, our nonperturbative calculations account for the electron-phonon interaction on an equal footing with couplings to the leads, as well as the coupling between the two dots. Our results exhibit oscillations in both the current and shot noise as functions of the energy difference between the two QDs, resulting from the spontaneous emission of phonons in the nonlinear transport process. In the "zero-phonon" resonant tunneling regime, the shot noise exhibits a double peak, while in the "one-phonon" region, only a single peak appears.Comment: 10 pages, 6 figures, some minor changes, accepted by Phys. Rev.

Invisible hands behind 3.5GHz spectrum sharing

There has been considerable discussion surrounding the barriers to spectrum sharing in the literature. Among those is the ‘trust gap’ that exists, according to the PCAST report. Trust is a complex human construct that significantly includes risk. In this paper, we examine the risks faced by the different user classes proposed by the FCC for sharing in the 3.5 GHz band. We argue that the “invisible hands” of spectrum sharing in this band is the balance between spectrum sharing gain and associated risks. We find that both gains and risks can be linked to the distance between incumbents’ systems and Citizen Broadband Radio Services (CBRS)’ systems. The risk portfolio is linked to spectrum rights that each tier has, since the rights they have determine risks and risk mitigation strategies. We further propose a model to calculate spectrum sharing utilities for different tiers. The optimized utility determines the distance between incumbents and CBRS systems

Nonlinear dynamics of a cigar-shaped Bose-Einstein condensate coupled with a single cavity mode

We investigate the nonlinear dynamics of a combined system which is composed of a cigar-shaped Bose-Einstein condensate and an optical cavity. The two sides couple dispersively. This system is characterized by its nonlinearity: after integrating out the freedom of the cavity mode, the potential felt by the condensate depends on the condensate itself. We develop a discrete-mode approximation for the condensate. Based on this approximation, we map out the steady configurations of the system. It is found that due to the nonlinearity of the system, the nonlinear levels of the system can fold up in some parameter regimes. That will lead to the breakdown of adiabaticity. Analysis of the dynamical stability of the steady states indicates that the same level structure also results in optical bistability.Comment: 8 pages, 5 figure

Topology of Entanglement in Multipartite States with Translational Invariance

The topology of entanglement in multipartite states with translational invariance is discussed in this article. Two global features are foundby which one can distinguish distinct states. These are the cyclic unit and the quantised geometric phase. Furthermore the topology is indicated by the fractional spin. Finally a scheme is presented for preparation of these types of states in spin chain systems, in which the degeneracy of the energy levels characterises the robustness of the states with translational invariance.Comment: major revision. accepted by EPJ

Vector magnetic field sensing by single nitrogen vacancy center in diamond

In this Letter, we proposed and experimentally demonstrated a method to detect vector magnetic field with a single nitrogen vacancy (NV) center in diamond. The magnetic field in parallel with the axis of the NV center can be obtained by detecting the electron Zeeman shift, while the Larmor precession of an ancillary nuclear spin close to the NV center can be used to measure the field perpendicular to the axis. Experimentally, both the Zeeman shift and Larmor precession can be measured through the fluorescence from the NV center. By applying additional calibrated magnetic fields, complete information of the vector magnetic field can be achieved with such a method. This vector magnetic field detection method is insensitive to temperature fluctuation and it can be applied to nanoscale magnetic measurement.Comment: 5 pages, 5 figure

Opaque Service Virtualisation: A Practical Tool for Emulating Endpoint Systems

Large enterprise software systems make many complex interactions with other services in their environment. Developing and testing for production-like conditions is therefore a very challenging task. Current approaches include emulation of dependent services using either explicit modelling or record-and-replay approaches. Models require deep knowledge of the target services while record-and-replay is limited in accuracy. Both face developmental and scaling issues. We present a new technique that improves the accuracy of record-and-replay approaches, without requiring prior knowledge of the service protocols. The approach uses Multiple Sequence Alignment to derive message prototypes from recorded system interactions and a scheme to match incoming request messages against prototypes to generate response messages. We use a modified Needleman-Wunsch algorithm for distance calculation during message matching. Our approach has shown greater than 99% accuracy for four evaluated enterprise system messaging protocols. The approach has been successfully integrated into the CA Service Virtualization commercial product to complement its existing techniques.Comment: In Proceedings of the 38th International Conference on Software Engineering Companion (pp. 202-211). arXiv admin note: text overlap with arXiv:1510.0142