Dynamical Cluster Quantum Monte Carlo Study of the Single Particle Spectra of Strongly Interacting Fermion Gases

We study the single-particle spectral function of resonantly-interacting fermions in the unitary regime, as described by the three-dimensional attractive Hubbard model in the dilute limit. Our approach, based on the Dynamical Cluster Approximation and the Maximum Entropy Method, shows the emergence of a gap with decreasing temperature, as reported in recent cold-atom photoemission experiments, for coupling values that span the BEC-BCS crossover. By comparing the behavior of the spectral function to that of the imaginary time dynamical pairing susceptibility, we attribute the development of the gap to the formation of local bound atom pairs.Comment: 4 pages, 4 figures, accepted by PRA Rapid Communication

Spin dynamics of two-dimensional electrons with Rashba spin-orbit coupling and electron-electron interactions

We study the spin dynamics of two dimensional electron gases (2DEGs) with Rashba spin-orbit coupling by taking account of electron-electron interactions. The diffusion equations for charge and spin densities are derived by making use of the path-integral approach and the quasiclassical Green's function. Analyzing the effect of the interactions, we show that the spin-relaxation time can be enhanced by the electron-electron interaction in the ballistic regime.Comment: accepted for publication in Phys. Rev.

Quantum-Classical Transition of Photon-Carnot Engine Induced by Quantum Decoherence

We study the physical implementation of the Photon Carnot engine (PCE) based on the cavity QED system [M. Scully et al, Science, \textbf{299}, 862 (2003)]. Here, we analyze two decoherence mechanisms for the more practical systems of PCE, the dissipation of photon field and the pure dephasing of the input atoms. As a result we find that (I) the PCE can work well to some extent even in the existence of the cavity loss (photon dissipation); and (II) the short-time atomic dephasing, which can destroy the PCE, is a fatal problem to be overcome.Comment: 6 pages, 3 figure

Comparative experimental study of local mixing of active and passive scalars in turbulent thermal convection

We investigate experimentally the statistical properties of active and passive scalar fields in turbulent Rayleigh-B\'{e}nard convection in water, at $Ra\sim10^{10}$. Both the local concentration of fluorescence dye and the local temperature are measured near the sidewall of a rectangular cell. It is found that, although they are advected by the same turbulent flow, the two scalars distribute differently. This difference is twofold, i.e. both the quantities themselves and their small-scale increments have different distributions. Our results show that there is a certain buoyant scale based on time domain, i.e. the Bolgiano time scale $t_B$, above which buoyancy effects are significant. Above $t_B$, temperature is active and is found to be more intermittent than concentration, which is passive. This suggests that the active scalar possesses a higher level of intermittency in turbulent thermal convection. It is further found that the mixing of both scalar fields are isotropic for scales larger than $t_B$ even though buoyancy acts on the fluid in the vertical direction. Below $t_B$, temperature is passive and is found to be more anisotropic than concentration. But this higher degree of anisotropy is attributed to the higher diffusivity of temperature over that of concentration. From the simultaneous measurements of temperature and concentration, it is shown that two scalars have similar autocorrelation functions and there is a strong and positive correlation between them.Comment: 13 pages and 12 figure

Spatiotemporal complexity of a ratio-dependent predator-prey system

In this paper, we investigate the emergence of a ratio-dependent predator-prey system with Michaelis-Menten-type functional response and reaction-diffusion. We derive the conditions for Hopf, Turing and Wave bifurcation on a spatial domain. Furthermore, we present a theoretical analysis of evolutionary processes that involves organisms distribution and their interaction of spatially distributed population with local diffusion. The results of numerical simulations reveal that the typical dynamics of population density variation is the formation of isolated groups, i.e., stripelike or spotted or coexistence of both. Our study shows that the spatially extended model has not only more complex dynamic patterns in the space, but also chaos and spiral waves. It may help us better understand the dynamics of an aquatic community in a real marine environment.Comment: 6pages, revtex

Spin relaxation of two-dimensional electrons with a hierarchy of spin-orbit couplings

The density matrix formalism is applied to calculate the spin-relaxation time for two-dimensional systems with a hierarchy of spin-orbit couplings, such as Rashba-type, Dresselhaus-type and so on. It is found that the spin-relaxation time can be infinite if those coupling strengths $\alpha$, $\beta$, $\gamma_1$ and $\gamma_2$ satisfy either condition (i) $\alpha=\beta, \gamma_1=0$ or (ii) $\alpha=-\beta, \gamma_2=0$, which correspond to the vanishing Yang-Mills "magnetic" field. The effect caused by the application of an external magnetic field is also discussed. It is found that the longitudinal and in-plane spin components can possess infinite life time when the spin components, the Larmor precession frequency and the external magnetic field satisfy certain relations.Comment: Revtex, 7 pages, 3 figure

Quantum Thermodynamic Cycles and quantum heat engines

In order to describe quantum heat engines, here we systematically study isothermal and isochoric processes for quantum thermodynamic cycles. Based on these results the quantum versions of both the Carnot heat engine and the Otto heat engine are defined without ambiguities. We also study the properties of quantum Carnot and Otto heat engines in comparison with their classical counterparts. Relations and mappings between these two quantum heat engines are also investigated by considering their respective quantum thermodynamic processes. In addition, we discuss the role of Maxwell's demon in quantum thermodynamic cycles. We find that there is no violation of the second law, even in the existence of such a demon, when the demon is included correctly as part of the working substance of the heat engine.Comment: 17 pages, 9 figures, 4 table