29,273 research outputs found

### Inference from Matrix Products: A Heuristic Spin Glass Algorithm

We present an algorithm for finding ground states of two dimensional spin
glass systems based on ideas from matrix product states in quantum information
theory. The algorithm works directly at zero temperature and defines an
approximate "boundary Hamiltonian" whose accuracy depends on a parameter $k$.
We test the algorithm against exact methods on random field and random bond
Ising models, and we find that accurate results require a $k$ which scales
roughly polynomially with the system size. The algorithm also performs well
when tested on small systems with arbitrary interactions, where no fast, exact
algorithms exist. The time required is significantly less than Monte Carlo
schemes.Comment: 4 pages, 1 figure, minor typos fixe

### Electromagnetic Interaction in the System of Multimonopoles and Vortex Rings

Behavior of static axially symmetric monopole-antimonopole and vortex ring
solutions of the SU(2) Yang-Mills-Higgs theory in an external uniform magnetic
field is considered. It is argued that the axially symmetric
monopole-antimonopole chains and vortex rings can be treated as a bounded
electromagnetic system of the magnetic charges and the electric current rings.
The magnitude of the external field is a parameter which may be used to test
the structure of the static potential of the effective electromagnetic
interaction between the monopoles with opposite orientation in the group space.
It is shown that for a non-BPS solutions there is a local minimum of this
potential.Comment: 10 pages, 12 figures, some minor corrections, version to appear in
Phys. Rev.

### Migration of bosonic particles across a Mott insulator to superfluid phase interface

We consider a boundary between a Mott insulator and a superfluid region of a
Bose-Hubbard model at unit filling. Initially both regions are decoupled and
cooled to their respective ground states. We show that, after switching on a
small tunneling rate between both regions, all particles of the Mott region
migrate to the superfluid area. This migration takes place whenever the
difference between the chemical potentials of both regions is less than the
maximal energy of any eigenmode of the superfluid. We verify our results
numerically with DMRG simulations and explain them analytically with a master
equation approximation, finding good agreement between both approaches. Finally
we carry out a feasibility study for the observation of the effect in coupled
arrays of micro-cavities and optical lattices.Comment: 5 pages, 6 figures, to appear in Phys. Rev. Let

### Critical behavior of the Random-Field Ising Magnet with long range correlated disorder

We study the correlated-disorder driven zero-temperature phase transition of
the Random-Field Ising Magnet using exact numerical ground-state calculations
for cubic lattices. We consider correlations of the quenched disorder decaying
proportional to r^a, where r is the distance between two lattice sites and a<0.
To obtain exact ground states, we use a well established mapping to the
graph-theoretical maximum-flow problem, which allows us to study large system
sizes of more than two million spins. We use finite-size scaling analyses for
values a={-1,-2,-3,-7} to calculate the critical point and the critical
exponents characterizing the behavior of the specific heat, magnetization,
susceptibility and of the correlation length close to the critical point. We
find basically the same critical behavior as for the RFIM with delta-correlated
disorder, except for the finite-size exponent of the susceptibility and for the
case a=-1, where the results are also compatible with a phase transition at
infinitesimal disorder strength.
A summary of this work can be found at the papercore database at
www.papercore.org.Comment: 9 pages, 13 figure

### Monopoles and dyons in SO(3) gauged Skyrme models

Three dimensional SO(3) gauged Skyrme models characterised by specific
potentials imposing special asymptotic values on the chiral field are
considered. These models are shown to support finite energy solutions with
nonvanishing magnetic and electrix flux, whose energies are bounded from below
by two distinct charges - the magnetic (monopole) charge and a non-integer
version of the Baryon charge. Unit magnetic charge solutions are constructed
numerically and their properties characterised by the chosen asymptotics and
the Skyrme coupling are studied. For a particular value of the chosen
asymptotics, charge-2 axially symmetric solutions are also constructed and the
attractive nature of the like-monopoles of this system are exhibited. As an
indication towards the possible existence of large clumps of monopoles, some
consideration is given to axially symmetric monopoles of charges-2,3,4.Comment: 15 pages, 4 Postscript figure

### Direct sampling of complex landscapes at low temperatures: the three-dimensional +/-J Ising spin glass

A method is presented, which allows to sample directly low-temperature
configurations of glassy systems, like spin glasses. The basic idea is to
generate ground states and low lying excited configurations using a heuristic
algorithm. Then, with the help of microcanonical Monte Carlo simulations, more
configurations are found, clusters of configurations are determined and
entropies evaluated. Finally equilibrium configuration are randomly sampled
with proper Gibbs-Boltzmann weights.
The method is applied to three-dimensional Ising spin glasses with +- J
interactions and temperatures T<=0.5. The low-temperature behavior of this
model is characterized by evaluating different overlap quantities, exhibiting a
complex low-energy landscape for T>0, while the T=0 behavior appears to be less
complex.Comment: 9 pages, 7 figures, revtex (one sentence changed compared to v2

### Generation of mesoscopic entangled states in a cavity coupled to an atomic ensemble

We propose a novel scheme for the efficient production of "NOON states" based
on the resonant interaction of a pair of quantized cavity modes with an
ensemble of atoms. We show that in the strong-coupling regime the adiabatic
evolution of the system tends to a limiting state that describes mesoscopic
entanglement between photons and atoms which can easily be converted to a
purely photonic or atomic NOON state. We also demonstrate the remarkable
property that the efficiency of this scheme increases exponentially with the
cavity cooperativity factor, which gives efficient access to high number NOON
states. The experimental feasibility of the scheme is discussed and its
efficiency is demonstrated numerically.Comment: 4 pages, 3 figure

### Steady state entanglement in the mechanical vibrations of two dielectric membranes

We consider two dielectric membranes suspended inside a Fabry-Perot-cavity,
which are cooled to a steady state via a drive by suitable classical lasers. We
show that the vibrations of the membranes can be entangled in this steady
state. They thus form two mechanical, macroscopic degrees of freedom that share
steady state entanglement.Comment: example for higher environment temperatures added, further
explanations added to the tex

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