12,464 research outputs found
Anticommutative extension of the Adler map
We construct a noncommutative (Grassmann) extension of the well-known Adler Yang–Baxter map. It satisfies the Yang–Baxter equation, it is reversible and birational. Our extension preserves all the properties of the original map except the involutivity
Materials processing with tightly focused femtosecond vortex laser beams
This letter is the first demonstration of material modification using tightly
focused femtosecond laser vortex beams. Double-charge femtosecond vortices were
synthesized with the polarization-singularity beam converter described in Ref
[1] and then focused using moderate and high numerical aperture optics (viz.,
NA = 0.45 and 0.9) to ablate fused silica and soda-lime glasses. By controlling
the pulse energy we consistently machine high-quality micron-size ring-shaped
structures with less than 100 nm uniform groove thickness.Comment: 8 pages, 3 figures, 10 references; submitted to Appl. Phys. Lett. on
May 31, 201
Dynamical Casimir Effect for a Swinging Cavity
The resonant scalar particle generation for a swinging cavity resonator in
the Casimir vacuum is examined. It is shown that the number of particles grows
exponentially when the cavity rotates at some specific external frequency.Comment: to appear in J. Phys. A: Math. Theo
Comment on "Two Phase Transitions in the Fully frustrated XY Model"
The conclusions of a recent paper by Olsson (Phys. Rev. Lett. 75, 2758
(1995), cond-mat/9506082) about the fully frustrated XY model in two dimensions
are questioned. In particular, the evidence presented for having two separate
chiral and U(1) phase transitions are critically considered.Comment: One page one table, to Appear in Physical Review Letter
Reentrant Peak Effect in an anisotropic superconductor 2H-NbSe_2 : Role of disorder
The reentrant nature of Peak Effect is established in a single crystal of
2H-NbSe_2 via electrical transport and dc magnetisation studies. The role of
disorder on the reentrant branch of PE has been examined in three single
crystals with varying levels of quenched random disorder. Increasing disorder
presumably shrinks the (H,T) parameter space over which vortex array retains
spatial order. Although, the upper branch of the PE curve is somewhat robust,
the lower reentrant branch of the same curve is strongly affected by disorder.Comment: 5 Pages of text, 4 figure
Coarse-Graining the Lin-Maldacena Geometries
The Lin-Maldacena geometries are nonsingular gravity duals to degenerate
vacuum states of a family of field theories with SU(2|4) supersymmetry. In this
note, we show that at large N, where the number of vacuum states is large,
there is a natural `macroscopic' description of typical states, giving rise to
a set of coarse-grained geometries. For a given coarse-grained state, we can
associate an entropy related to the number of underlying microstates. We find a
simple formula for this entropy in terms of the data that specify the geometry.
We see that this entropy function is zero for the original microstate
geometries and maximized for a certain ``typical state'' geometry, which we
argue is the gravity dual to the zero-temperature limit of the thermal state of
the corresponding field theory. Finally, we note that the coarse-grained
geometries are singular if and only if the entropy function is non-zero.Comment: 29 pages, LaTeX, 3 figures; v2 references adde
String-Net Models with Fusion Algebra
We study the Levin-Wen string-net model with a type fusion algebra.
Solutions of the local constraints of this model correspond to gauge
theory and double Chern-simons theories with quantum groups. For the first
time, we explicitly construct a spin- model with gauge symmetry
on a triangular lattice as an exact dual model of the string-net model with a
type fusion algebra on a honeycomb lattice. This exact duality exists
only when the spins are coupled to a gauge field living on the links of
the triangular lattice. The ungauged lattice spin models are a class of
quantum systems that bear symmetry-protected topological phases that may be
classified by the third cohomology group of . Our results
apply also to any case where the fusion algebra is identified with a finite
group algebra or a quantusm group algebra.Comment: 16 pages, 2 figures, publishe
Operator-sum representation of time-dependent density operators and its applications
We show that any arbitrary time-dependent density operator of an open system
can always be described in terms of an operator-sum representation regardless
of its initial condition and the path of its evolution in the state space, and
we provide a general expression of Kraus operators for arbitrary time-dependent
density operator of an -dimensional system. Moreover, applications of our
result are illustrated through several examples.Comment: 4 pages, no figure, brief repor
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