54,581 research outputs found
Decoherence of interacting Majorana modes
We study the decoherence of Majorana modes of a fermion chain, where the
fermions interact with their nearest neighbours. We investigate the effect of
dissipation and dephasing on the Majorana modes of a fermionic chain. The
dissipative and dephasing noises induce the non-parity- and parity-preserving
transitions between the eigenstates of the system, respectively. Therefore,
these two types of noises lead to the different decoherence mechanisms. In each
type of noise, we discuss the low- and high-frequency regimes to describe the
different environments. We numerically calculate the dissipation and dephasing
rates in the presence of long-range interactions. We find that the decoherence
rate of interacting Majorana modes is different to that of non-interacting
modes. We show the examples that the long-range interactions can reduce the
decoherence rate. It is advantageous to the potential applications of quantum
information processing.Comment: 11 pages, 14 figure
Topological phases in spin-orbit coupled dipolar lattice bosons
We study the topological phases in spin-orbit coupled dipolar bosons in a
one-dimensional optical lattice. The magnetic dipolar interactions between
atoms give rise to the inter-site interactions. In the Mott-insulating regime,
this system can be described by the quantum XYZ spin model with the
Dzyaloshinskii-Moriya interactions in a transverse field. We focus on
investigating the effect of dipolar interactions on the topological phase. The
topological phase can be shown when spin-orbit coupling incorporates with the
repulsive dipolar interaction. We find that the dipolar interaction can broaden
the range of parameters of spin-orbit coupling and transverse field for
exhibiting the topological phase. The sum of spin correlations between the two
nearest neighbouring atoms can be used to indicate the topological phase. This
may be useful for detecting topological phases in experiments.Comment: 6 pages, 5 figures, revised versio
Quantum-limited measurement of magnetic-field gradient with entangled atoms
We propose a method to detect the microwave magnetic-field gradient by using
a pair of entangled two-component Bose-Einstein condensates. We consider the
two spatially separated condensates to be coupled to the two different magnetic
fields. The magnetic-field gradient can be determined by measuring the
variances of population differences and relative phases between the
two-component condensates in two wells. The precision of measurement can reach
the Heisenberg limit. We study the effects of one-body and two-body atom losses
on the detection. We find that the entangled atoms can outperform the
uncorrelated atoms in probing the magnetic fields in the presence of atom
losses. The effect of atom-atom interactions is also discussed.Comment: 8 pages, 12 figure
Production of mesoscopic superpositions with ultracold atoms
We study mesoscopic superpositions of two component Bose-Einstein
condensates. Atomic condensates, with long coherence times, are good systems in
which to study such quantum phenomenon. We show that the mesoscopic
superposition states can be rapidly generated in which the atoms dispersively
interact with the photon field in a cavity. We also discuss the production of
compass states which are generalized Schr\"{o}dinger cat states. The physical
realization of mesoscopic states is important in studying decoherence and
precision measurement.Comment: 4 pages, 2 figure
Particle-hole entanglement of ultracold atoms in an optical lattice
We study the ground state of two-component bosonic atoms in a one-dimensional
optical lattice. By applying an external field to the atoms at one end of
lattice, the atoms are transported and becomes localized at that site. The
holes are then created in the remaining sites. The particle-hole superpositions
are produced in this process. We investigate the entanglement entropy between
the atoms in the two different parts of a lattice. A large degree of
particle-hole entanglement is generated in the ground state. The particle-hole
quantum correlations can be probed by the two-site parity correlation
functions. The transport properties of the low-lying excited states are also
discussed.Comment: 5 pages, 8 figure
Nonequilibrium dynamics of spin-orbit coupled lattice bosons
We study the non-equilibrium dynamics of two component bosonic atoms in a
one-dimensional optical lattice in the presence of spin-orbit coupling. In the
Mott insulating regime, the two-component bosonic system at unity filling can
be described by the quantum spin XXZ model. The atoms are initially prepared in
their lower spin states. The system becomes out of equilibrium by suddenly
introducing spin-orbit coupling to the atoms. The system shows the relaxation
and non-stationary dynamics, respectively, in the different interaction
regimes. We find that the time average of magnetization is useful to
characterize the many-body dynamics. The effects of even and odd numbers of
sites are discussed. Our result sheds light on non-equilibrium dynamics due to
the interplay between spin-orbit coupling and atomic interactions.Comment: 8 pages, 6 figure
An iterative approach for amplitude amplification with nonorthogonal measurements
Using three coupled harmonic oscillators, we present an
amplitude-amplification method for factorization of an integer. We generalize
the method in [arXiv:1007.4338] by employing non-orthogonal measurements on the
harmonic oscillator. This method can increase the probability of obtaining the
factors by repeatedly using the nonlinear interactions between the oscillators
and non-orthogonal measurements. However, this approach requires an exponential
amount of resources for implementation. Thus, this method cannot provide a
speed-up over classical algorithms unless its limitations are resolved.Comment: 21 pages, 5 figures; title changed, major revision
Quantum estimation of magnetic-field gradient using W-state
We study the precision limits of detecting a linear magnetic-field gradient
by using W-states in the presence of different types of noises. We consider to
use an atomic spin chain for probing the magnetic-field gradient, where a
W-state is prepared. We compare this method with the measurement of using two
uncorrelated atoms. For pure states, W-states can provide an improvement over
uncorrelated states in determining the magnetic-field gradient up to four
particles. We examine the effects of local dephasing and dissipations on the
performances of detections. In presence of dephasing, the uncorrelated atoms
can give a higher precision than using W-states. But W-states provide a better
performance in the presence of dissipation for a few particles. We briefly
discuss the implementation of the detection methods with cold atoms and trapped
ions.Comment: 7 pages and 5 figures, title changed, updated version with
clarificatio
Vacuum Fluctuations induced Entanglement between Two Mesoscopic Systems
We study the dynamics of a pair of molecular ensembles trapped inside a
superconducting resonator through which they are strongly coupled via a
microwave field mode. We find that entanglement can be generated via "vacuum
fluctuations" even when the molecules and cavity field are initially prepared
in their ground state. This entanglement is created in a relatively short time
and without the need for further manipulation of the system. It does,
therefore, provide a convenient scheme to entangle two mesoscopic systems, and
may well be useful quantum information processing.Comment: 4 pages, 4 figure
Comment on "Uncertainty in measurements of distance"
We have argued that quantum mechanics and general relativity give a lower
bound on the measurement uncertainty of
any distance much greater than the Planck length . Recently Baez and
Olson have claimed that one can go below this bound by attaching the measuring
device to a massive elastic rod. Here we refute their claim. We also reiterate
(and invite our critics to ponder on) the intimate relationship and consistency
between black hole physics (including the holographic principle) and our bound
on distance measurements.Comment: 4 pages, aaste
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