Quench induced Mott insulator to superfluid quantum phase transition

Mott insulator to superfluid quenches have been used by recent experiments to generate exotic superfluid phases. While the final Hamiltonian following the sudden quench is that of a superfluid, it is not a priori clear how close the final state of the system approaches the ground state of the superfluid Hamiltonian. To understand the nature of the final state we calculate the temporal evolution of the momentum distribution following a Mott insulator to superfluid quench. Using the numerical infinite time-evolving block decimation approach and the analytical rotor model approximation we establish that the one and two dimensional Mott insulators following the quench equilibriate to thermal states with spatially short-ranged coherence peaks in the final momentum distribution and therefore are not strict superfluids. However, in three dimensions we find a divergence in the momentum distribution indicating the emergence of true superfluid order.Comment: 4.2 pages, 3 Figure

Stability of BTZ black strings

We study the dynamical stability of the BTZ black string against fermonic and gravitational perturbations. The BTZ black string is not always stable against these perturbations. There exist threshold values for $m^2$ related to the compactification of the extra dimension for fermonic perturbation, scalar part of the gravitational perturbation and the tensor perturbation, respectively. Above the threshold values, perturbations are stable; while below these thresholds, perturbations can be unstable. We find that this non-trivial stability behavior qualitatively agrees with that predicted by a thermodynamical argument, showing that the BTZ black string phase is not the privileged stable phase.Comment: 9 pages, revised version to appear in Phys. Rev.

Aharonov-Bohm Oscillation and Chirality Effect in Optical Activity of Single Wall Carbon Nanotubes

We study the Aharonov-Bohm effect in the optical phenomena of single wall carbon nanotubes (SWCN) and also their chirality dependence. Specially, we consider the natural optical activity as a proper observable and derive it's general expression based on a comprehensive symmetry analysis, which reveals the interplay between the enclosed magnetic flux and the tubule chirality for arbitrary chiral SWCN. A quantitative result for this optical property is given by a gauge invariant tight-binding approximation calculation to stimulate experimental measurements.Comment: Submitted on 15 Jan 04, REVISED on 28 Apr 04, To appear in Phys. Rev. B(Brief Report

Measurable nonlocal effect of bipartite system during a local cyclic evolution of its subsystem

In this letter, a nonlocal effect for a bipartite system which is induced by a local cyclic evolution of one of its subsystem is suggested. This effect vanishes when the system is at a disentangled pure state but can be observed for some disentangled mixed states. As a paradigm, we study the effect for the system of two qubits in detail. It is interesting that the effect is directly related to the degree of entanglement for pure state of qubit pairs. Furthermore, we suggest a Bell-type experiment to measure this nonlocal effect for qubit pairs.Comment: 5 pages, 2 figure

A Comprehensive Analysis of Swift/XRT Data: III. Jet Break Candidates in X-ray and Optical Afterglow Lightcurves

The Swift/XRT data of 179 GRBs (from 050124 to 070129) and the optical afterglow data of 57 pre- and post-Swift GRBs are analyzed, in order to systematically investigate the jet-like breaks in the X-ray and optical afterglow lightcurves. We find that not a single burst can be included in the ``Platinum'' sample, in which the data satisfy all the criteria of a jet break. By releasing one or more requirements to define a jet break, some candidates of various degrees could be identified. In the X-ray band, 42 out of the 103 well-sampled X-ray lightcurves have a decay slope of the post-break segment >1.5 (``Bronze'' sample), and 27 of them also satisfy the closure relations of the forward models (``Silver'' sample). The numbers of the ``Bronze'' and ``Silver'' candidates in the optical lightcurves are 27 and 23, respectively. Thirteen bursts have well-sampled optical and X-ray lightcurves, but only seven cases are consistent with an achromatic break, but even in these cases only one band satisfies the closure relations (``Gold'' sample). The observed break time in the XRT lightcurves is systematically earlier than that in the optical bands. All these raise great concerns in interpreting the jet-like breaks as jet breaks and further inferring GRB energetics from these breaks. By assuming that these breaks are jet breaks, we perform a similar analysis as previous work to calculate the jet opening angle (theta_j) and energetics (E_k) with the ``Silver'' and ``Gold'' jet break candidates. The derived E_K distribution reveals a much larger scatter than the pre-Swift sample. A tentative anti-correlation between theta_j and E_{K,iso} is found for both the pre-Swift and Swift GRBs, indicating that the E_K could still be quasi-universal, if the breaks in discussion are indeed jet breaks(abridge).Comment: 48 pages, including 5 tables and 8 figures. Accepted for publication in ApJ. This is the third paper of a series. Paper I and II see astro-ph/0612246 (ApJ, 2007, 666,1002) and arXiv:0705.1373 (ApJ, 2007, 669, n2,in press

Simple scheme for implementing the Deutsch-Jozsa algorithm in thermal cavity

We present a simple scheme to implement the Deutsch-Jozsa algorithm based on two-atom interaction in a thermal cavity. The photon-number-dependent parts in the evolution operator are canceled with the strong resonant classical field added. As a result, our scheme is immune to thermal field, and does not require the cavity to remain in the vacuum state throughout the procedure. Besides, large detuning between the atoms and the cavity is not necessary neither, leading to potential speed up of quantum operation. Finally, we show by numerical simulation that the proposed scheme is equal to demonstrate the Deutsch-Jozsa algorithm with high fidelity.Comment: 7 pages, 4 figure

Spatially and Spectrally Resolved Observations of a Zebra Pattern in Solar Decimetric Radio Burst

We present the first interferometric observation of a zebra-pattern radio burst with simultaneous high spectral (~ 1 MHz) and high time (20 ms) resolution. The Frequency-Agile Solar Radiotelescope (FASR) Subsystem Testbed (FST) and the Owens Valley Solar Array (OVSA) were used in parallel to observe the X1.5 flare on 14 December 2006. By using OVSA to calibrate the FST the source position of the zebra pattern can be located on the solar disk. With the help of multi-wavelength observations and a nonlinear force-free field (NLFFF) extrapolation, the zebra source is explored in relation to the magnetic field configuration. New constraints are placed on the source size and position as a function of frequency and time. We conclude that the zebra burst is consistent with a double-plasma resonance (DPR) model in which the radio emission occurs in resonance layers where the upper hybrid frequency is harmonically related to the electron cyclotron frequency in a coronal magnetic loop.Comment: Accepted for publication in Ap