17,539 research outputs found
Non-Linear Sigma Models on a Half Plane
In the context of integrable field theory with boundary, the integrable
non-linear sigma models in two dimensions, for example, the , the
principal chiral, the and the complex Grassmannian sigma
models are discussed on a half plane. In contrast to the well known cases of
sine-Gordon, non-linear Schr\"odinger and affine Toda field theories, these
non-linear sigma models in two dimensions are not classically integrable if
restricted on a half plane. It is shown that the infinite set of non-local
charges characterising the integrability on the whole plane is not conserved
for the free (Neumann) boundary condition. If we require that these non-local
charges to be conserved, then the solutions become trivial.Comment: 25 pages, latex, no figure
A note on the equivalence of a barotropic perfect fluid with a K-essence scalar field
In this short note, we obtain the necessary and sufficient condition for a
class of non-canonical single scalar field models to be exactly equivalent to
barotropic perfect fluids, under the assumption of an irrotational fluid flow.
An immediate consequence of this result is that the non-adiabatic pressure
perturbation in this class of scalar field systems vanishes exactly at all
orders in perturbation theory and on all scales. The Lagrangian for this
general class of scalar field models depends on both the kinetic term and the
value of the field. However, after a field redefinition, it can be effectively
cast in the form of a purely kinetic K-essence model.Comment: 4 pages, 1 figure; v2: References and footnotes 3 and 4 added.
Replaced to match published versio
Demonstration of an optical quantum controlled-NOT gate without path interference
We report the first experimental demonstration of an optical quantum
controlled-NOT gate without any path interference, where the two interacting
path interferometers of the original proposals (Phys. Rev. A {\bf 66}, 024308
(2001), Phys. Rev. A {\bf 65}, 012314 (2002)) have been replaced by three
partially polarizing beam splitters with suitable polarization dependent
transmittances and reflectances. The performance of the device is evaluated
using a recently proposed method (Phys. Rev. Lett. {\bf 94}, 160504 (2005)), by
which the quantum process fidelity and the entanglement capability can be
estimated from the 32 measurement results of two classical truth tables,
significantly less than the 256 measurement results required for full quantum
tomography.Comment: 4 pages, 3 figure
Temperature Chaos, Rejuvenation and Memory in Migdal-Kadanoff Spin Glasses
We use simulations within the Migdal-Kadanoff real space renormalization
approach to probe the scales relevant for rejuvenation and memory in spin
glasses. One of the central questions concerns the role of temperature chaos.
First we investigate scaling laws of equilibrium temperature chaos, finding
super-exponential decay of correlations but no chaos for the total free energy.
Then we perform out of equilibrium simulations that follow experimental
protocols. We find that: (1) rejuvenation arises at a length scale smaller than
the ``overlap length'' l(T,T'); (2) memory survives even if equilibration goes
out to length scales much larger than l(T,T').Comment: 4 pages, 4 figures, added references, slightly changed content,
modified Fig.
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