Gate control of a quantum dot single-electron spin in realistic confining potentials: anisotropy effects

Among recent proposals for next-generation, non-charge-based logic is the notion that a single electron can be trapped and its spin can be manipulated through the application of gate potentials. In this paper, we present numerical simulations of such spins in single electron devices for realistic (asymmetric) confining potentials in two-dimensional electrostatically confined quantum dots. Using analytical and numerical techniques we show that breaking the in-plane rotational symmetry of the confining potential leads to a significant effect on the tunability of the g-factor with applied gate potentials. In particular, anisotropy extends the range of tunability to larger quantum dots.Comment: 7 pages, 13 figure

Fluctuation Theorems

Fluctuation theorems, which have been developed over the past 15 years, have resulted in fundamental breakthroughs in our understanding of how irreversibility emerges from reversible dynamics, and have provided new statistical mechanical relationships for free energy changes. They describe the statistical fluctuations in time-averaged properties of many-particle systems such as fluids driven to nonequilibrium states, and provide some of the very few analytical expressions that describe nonequilibrium states. Quantitative predictions on fluctuations in small systems that are monitored over short periods can also be made, and therefore the fluctuation theorems allow thermodynamic concepts to be extended to apply to finite systems. For this reason, fluctuation theorems are anticipated to play an important role in the design of nanotechnological devices and in understanding biological processes. These theorems, their physical significance and results for experimental and model systems are discussed.Comment: A review, submitted to Annual Reviews in Physical Chemistry, July 2007 Acknowledgements corrected in revisio

Annihilation of vortex dipoles in an Oblate Bose-Einstein Condensate

We theoretically explore the annihilation of vortex dipoles, generated when an obstacle moves through an oblate Bose-Einstein condensate, and examine the energetics of the annihilation event. We show that the gray soliton, which results from the vortex dipole annihilation, is lower in energy than the vortex dipole. We also investigate the annihilation events numerically and observe that the annihilation occurs only when the vortex dipole overtakes the obstacle and comes closer than the coherence length. Furthermore, we find that the noise reduces the probability of annihilation events. This may explain the lack of annihilation events in experimental realizations.Comment: 8 pages and 9 figure

Direct measurement of B(D_s^+ → φX^+)

The absolute inclusive branching fraction of D_s^+→φX^+ has been measured from data collected by the BES detector at a center-of-mass energy of 4.03 GeV, corresponding to an integrated luminosity of 22.3 pb^(-1). At this energy, direct pair production e^+e^-→D_s^+D_s^- has been observed. We have selected D_s candidate events by reconstructing five hadronic decay modes D_s^+→φπ^+, K^(0*)K^+, K^0K^+, f0^(π+) and K^0K^-π^+π^+ and have searched for inclusive φ’s in the recoiling D_s^-. We observed three recoiling φ’s in the 166.4 ± 31.8 D_s candidate events, which leads to the absolute branching fraction B(D_s^+→φX^+)=(17.8(-7.2 -6.3)^(+15.1+0.6)) % and B(D_s-6.3+→φπ-6.3+)=(3.6_(-1.6 -1.3)(^_3.1+0.4) %. [S0556-2821(97)02423-5

Measurement of the mass of the τ lepton

The mass of the τ lepton has been measured at the Beijing Electron-Positron Collider using the Beijing Spectrometer. A search near threshold for e^+e^-→τ^+τ^- was performed. Candidate events were identified by requiring that one τ decay via τ→eνν¯, and the other via τ→μνν¯. The mass value, obtained from a fit to the energy dependence of the τ^+τ^- cross section, is m_τ=1776.9_(-0.5)^(+0.4)±0.2 MeV

Penetration depth of low-coherence enhanced backscattered light in sub-diffusion regime

The mechanisms of photon propagation in random media in the diffusive multiple scattering regime have been previously studied using diffusion approximation. However, similar understanding in the low-order (sub-diffusion) scattering regime is not complete due to difficulties in tracking photons that undergo very few scatterings events. Recent developments in low-coherence enhanced backscattering (LEBS) overcome these difficulties and enable probing photons that travel very short distances and undergo only a few scattering events. In LEBS, enhanced backscattering is observed under illumination with spatial coherence length L_sc less than the scattering mean free path l_s. In order to understand the mechanisms of photon propagation in LEBS in the subdiffusion regime, it is imperative to develop analytical and numerical models that describe the statistical properties of photon trajectories. Here we derive the probability distribution of penetration depth of LEBS photons and report Monte Carlo numerical simulations to support our analytical results. Our results demonstrate that, surprisingly, the transport of photons that undergo low-order scattering events has only weak dependence on the optical properties of the medium (l_s and anisotropy factor g) and strong dependence on the spatial coherence length of illumination, L_sc, relative to those in the diffusion regime. More importantly, these low order scattering photons typically penetrate less than l_s into the medium due to low spatial coherence length of illumination and their penetration depth is proportional to the one-third power of the coherence volume (i.e. [l_s \pi L_sc^2 ]^1/3).Comment: 32 pages(including 7 figures), modified version to appear in Phys. Rev.

Generalized Mittag-Leffler functions in the theory of finite-size scaling for systems with strong anisotropy and/or long-range interaction

The difficulties arising in the investigation of finite-size scaling in $d$--dimensional O(n) systems with strong anisotropy and/or long-range interaction, decaying with the interparticle distance $r$ as $r^{-d-\sigma}$ ($0<\sigma\leq2$), are discussed. Some integral representations aiming at the simplification of the investigations are presented for the classical and quantum lattice sums that take place in the theory. Special attention is paid to a more general form allowing to treat both cases on an equal footing and in addition cases with strong anisotropic interactions and different geometries. The analysis is simplified further by expressing this general form in terms of a generalization of the Mittag-Leffler special functions. This turned out to be very useful for the extraction of asymptotic finite-size behaviours of the thermodynamic functions.Comment: Accepted for publication in J. Phys. A: Math. and Gen.; 14 pages. The manuscript has been improved to help reader

आँध्रप्रदेश के समुद्री मात्स्यिकी स्रोत - एक पर्यावलोकन

आँध्रप्रदेश के समुद्री मात्स्यिकी स्रोत - एक पर्यावलोक