29,538 research outputs found
Period halving of Persistent Currents in Mesoscopic Mobius ladders
We investigate the period halving of persistent currents(PCs) of
non-interacting electrons in isolated mesoscopic M\"{o}bius ladders without
disorder, pierced by Aharonov-Bhom flux. The mechanisms of the period halving
effect depend on the parity of the number of electrons as well as on the
interchain hopping. Although the data of PCs in mesoscopic systems are
sample-specific, some simple rules are found in the canonical ensemble average,
such as all the odd harmonics of the PCs disappear, and the signals of even
harmonics are non-negative. {PACS number(s): 73.23.Ra, 73.23.-b, 68.65.-k}Comment: 6 Pages with 3 EPS figure
Single-cluster dynamics for the random-cluster model
We formulate a single-cluster Monte Carlo algorithm for the simulation of the
random-cluster model. This algorithm is a generalization of the Wolff
single-cluster method for the -state Potts model to non-integer values
. Its results for static quantities are in a satisfactory agreement with
those of the existing Swendsen-Wang-Chayes-Machta (SWCM) algorithm, which
involves a full cluster decomposition of random-cluster configurations. We
explore the critical dynamics of this algorithm for several two-dimensional
Potts and random-cluster models. For integer , the single-cluster algorithm
can be reduced to the Wolff algorithm, for which case we find that the
autocorrelation functions decay almost purely exponentially, with dynamic
exponents , and for , and
4 respectively. For non-integer , the dynamical behavior of the
single-cluster algorithm appears to be very dissimilar to that of the SWCM
algorithm. For large critical systems, the autocorrelation function displays a
range of power-law behavior as a function of time. The dynamic exponents are
relatively large. We provide an explanation for this peculiar dynamic behavior.Comment: 7 figures, 4 table
Emergent O(n) Symmetry in a series of three-dimensional Potts Models
We study the q-state Potts model on the simple cubic lattice with
ferromagnetic interactions in one lattice direction, and antiferromagnetic
interactions in the two other directions. As the temperature T decreases, the
system undergoes a second-order phase transition that fits in the universality
class of the 3D O(n) model with n=q-1. This conclusion is based on the
estimated critical exponents, and histograms of the order parameter. At even
smaller T we find, for q=4 and 5, a first-order transition to a phase with a
different type of long-range order. This long-range order dissolves at T=0, and
the system effectively reduces to a disordered two-dimensional Potts
antiferromagnet. These results are obtained by means of Monte Carlo simulations
and finite-size scaling.Comment: 5 pages, 7 figures, accepted by Physical Review
Superluminal propagation of an optical pulse in a Doppler broadened three-state, single channel active Raman gain medium
Using a single channel active Raman gain medium we show a ns
advance time for an optical pulse of s propagating
through a 10 cm medium, a lead time that is comparable to what was reported
previously. In addition, we have verified experimentally all the features
associated with this single channel Raman gain system. Our results show that
the reported gain-assisted superluminal propagation should not be attributed to
the interference between the two frequencies of the pump field.Comment: 4 pages, 3 figure
Heralded Entanglement between Atomic Ensembles: Preparation, Decoherence, and Scaling
Heralded entanglement between collective excitations in two atomic ensembles
is probabilistically generated, stored, and converted to single photon fields.
By way of the concurrence, quantitative characterizations are reported for the
scaling behavior of entanglement with excitation probability and for the
temporal dynamics of various correlations resulting in the decay of
entanglement. A lower bound of the concurrence for the collective atomic state
of 0.9\pm 0.3 is inferred. The decay of entanglement as a function of storage
time is also observed, and related to the local dynamics.Comment: 4 page
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