24,027 research outputs found
Creation and Manipulation of Anyons in the Kitaev Model
We analyze the effect of local spin operators in the Kitaev model on the
honeycomb lattice. We show, in perturbation around the isolated-dimer limit,
that they create Abelian anyons together with fermionic excitations which are
likely to play a role in experiments. We derive the explicit form of the
operators creating and moving Abelian anyons without creating fermions and show
that it involves multi-spin operations. Finally, the important experimental
constraints stemming from our results are discussed.Comment: 4 pages, 3 figures, published versio
Hydrogen column density evaluations toward Capella: consequences on the interstellar deuterium abundance
The deuterium abundance evaluation in the direction of Capella has for a long
time been used as a reference for the local interstellar medium (ISM) within
our Galaxy. We show here that broad and weak HI components could be present on
the Capella line of sight, leading to a large new additional systematic
uncertainty on the N(HI) evaluation.
The D/H ratio toward Capella is found to be equal to 1.67 (+/-0.3)x10^-5 with
almost identical chi^2 for all the fits (this range includes only the
systematic error; the 2 sigma statistical one is almost negligible in
comparison). It is concluded that D/H evaluations over HI column densities
below 10^19 cm^-2 (even perhaps below 10^20 cm^-2 if demonstrated by additional
observations) may present larger uncertainties than previously anticipated. It
is mentionned that the D/O ratio might be a better tracer for DI variations in
the ISM as recently measured by the Far Ultraviolet Spectroscopic Explorer
(FUSE).Comment: Accepted for publication in the Astrophysical Journal Letter
On the energy saved by interlayer interactions in the superconducting state of cuprates
A Ginzburg-Landau-like functional is proposed reproducing the main low-energy
features of various possible high-Tc superconducting mechanisms involving
energy savings due to interlayer interactions. The functional may be used to
relate these savings to experimental quantities. Two examples are given,
involving the mean-field specific heat jump at Tc and the superconducting
fluctuations above Tc. Comparison with existing data suggests, e.g., that the
increase of Tc due to the so-called interlayer tunneling (ILT) mechanism of
interlayer kinetic-energy savings is negligible in optimally-doped Bi-2212.Comment: 12 pages, no figures. Version history: 21-aug-2003, first version
(available on http://arxiv.org/abs/cond-mat/0308423v1); 15-jan-2004, update
to match Europhys. Lett. publication (minor grammar changes, updates in
bibliography - e.g., refs. 5 and 26
Entanglement renormalization in fermionic systems
We demonstrate, in the context of quadratic fermion lattice models in one and
two spatial dimensions, the potential of entanglement renormalization (ER) to
define a proper real-space renormalization group transformation. Our results
show, for the first time, the validity of the multi-scale entanglement
renormalization ansatz (MERA) to describe ground states in two dimensions, even
at a quantum critical point. They also unveil a connection between the
performance of ER and the logarithmic violations of the boundary law for
entanglement in systems with a one-dimensional Fermi surface. ER is recast in
the language of creation/annihilation operators and correlation matrices.Comment: 5 pages, 4 figures Second appendix adde
Simulation of quantum dynamics with quantum optical systems
We propose the use of quantum optical systems to perform universal simulation
of quantum dynamics. Two specific implementations that require present
technology are put forward for illustrative purposes. The first scheme consists
of neutral atoms stored in optical lattices, while the second scheme consists
of ions stored in an array of micro--traps. Each atom (ion) supports a
two--level system, on which local unitary operations can be performed through a
laser beam. A raw interaction between neighboring two--level systems is
achieved by conditionally displacing the corresponding atoms (ions). Then,
average Hamiltonian techniques are used to achieve evolutions in time according
to a large class of Hamiltonians.Comment: 14 pages, 6 figure
Concurrence in collective models
We review the entanglement properties in collective models and their
relationship with quantum phase transitions. Focusing on the concurrence which
characterizes the two-spin entanglement, we show that for first-order
transition, this quantity is singular but continuous at the transition point,
contrary to the common belief. We also propose a conjecture for the concurrence
of arbitrary symmetric states which connects it with a recently proposed
criterion for bipartite entanglement.Comment: 8 pages, 2 figures, published versio
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