13,650 research outputs found
Propagation of a Dark Soliton in a Disordered Bose-Einstein Condensate
We consider the propagation of a dark soliton in a quasi 1D Bose-Einstein
condensate in presence of a random potential. This configuration involves
nonlinear effects and disorder, and we argue that, contrarily to the study of
stationary transmission coefficients through a nonlinear disordered slab, it is
a well defined problem. It is found that a dark soliton decays algebraically,
over a characteristic length which is independent of its initial velocity, and
much larger than both the healing length and the 1D scattering length of the
system. We also determine the characteristic decay time.Comment: 4 pages, 2 figure
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Interatomic Coulombic electron capture from first principles
Interatomic Coulombic electron capture (ICEC) is an environment-assisted process in which a free electron can efficiently attach to an ion, atom or molecule by transferring the excess energy to a neighboring species. Absolute cross sections are necessary to evaluate the relative importance of this process. In this work, we employ the R-matrix method to compute ab initio these cross sections for a singly charged neon ion embedded in small helium clusters. Our results show that the ICEC cross sections are several orders of magnitude higher than anticipated and dominate other competing processes. Electron energy loss spectra on an absolute scale are provided for the Ne+@He20 cluster. Such spectra exhibit an unambiguous signature of the ICEC process. The finding is expected to stimulate experimental observations
Looking for symmetric Bell inequalities
Finding all Bell inequalities for a given number of parties, measurement
settings, and measurement outcomes is in general a computationally hard task.
We show that all Bell inequalities which are symmetric under the exchange of
parties can be found by examining a symmetrized polytope which is simpler than
the full Bell polytope. As an illustration of our method, we generate 238885
new Bell inequalities and 1085 new Svetlichny inequalities. We find, in
particular, facet inequalities for Bell experiments involving two parties and
two measurement settings that are not of the
Collins-Gisin-Linden-Massar-Popescu type.Comment: Joined the associated website as an ancillary file, 17 pages, 1
figure, 1 tabl
Bell inequalities for three systems and arbitrarily many measurement outcomes
We present a family of Bell inequalities for three parties and arbitrarily
many outcomes, which can be seen as a natural generalization of the Mermin Bell
inequality. For a small number of outcomes, we verify that our inequalities
define facets of the polytope of local correlations. We investigate the quantum
violations of these inequalities, in particular with respect to the Hilbert
space dimension. We provide strong evidence that the maximal quantum violation
can only be reached using systems with local Hilbert space dimension exceeding
the number of measurement outcomes. This suggests that our inequalities can be
used as multipartite dimension witnesses.Comment: v1 6 pages, 4 tables; v2 Published version with minor typos correcte
Bilocal versus non-bilocal correlations in entanglement swapping experiments
Entanglement swapping is a process by which two initially independent quantum
systems can become entangled and generate nonlocal correlations. To
characterize such correlations, we compare them to those predicted by bilocal
models, where systems that are initially independent are described by
uncorrelated states. We extend in this paper the analysis of bilocal
correlations initiated in [Phys. Rev. Lett. 104, 170401 (2010)]. In particular,
we derive new Bell-type inequalities based on the bilocality assumption in
different scenarios, we study their possible quantum violations, and analyze
their resistance to experimental imperfections. The bilocality assumption,
being stronger than Bell's standard local causality assumption, lowers the
requirements for the demonstration of quantumness in entanglement swapping
experiments
Emergent particle-hole symmetry in spinful bosonic quantum Hall systems
When a fermionic quantum Hall system is projected into the lowest Landau
level, there is an exact particle-hole symmetry between filling fractions
and . We investigate whether a similar symmetry can emerge in bosonic
quantum Hall states, where it would connect states at filling fractions
and . We begin by showing that the particle-hole conjugate to a
composite fermion `Jain state' is another Jain state, obtained by reverse flux
attachment. We show how information such as the shift and the edge theory can
be obtained for states which are particle-hole conjugates. Using the techniques
of exact diagonalization and infinite density matrix renormalization group, we
study a system of two-component (i.e., spinful) bosons, interacting via a
-function potential. We first obtain real-space entanglement spectra
for the bosonic integer quantum Hall effect at , which plays the role of
a filled Landau level for the bosonic system. We then show that at
the system is described by a Jain state which is the particle-hole conjugate of
the Halperin (221) state at . We show a similar relationship between
non-singlet states at and . We also study the case of
, providing unambiguous evidence that the ground state is a composite
Fermi liquid. Taken together our results demonstrate that there is indeed an
emergent particle-hole symmetry in bosonic quantum Hall systems.Comment: 10 pages, 8 figures, 4 appendice
Tapping Thermodynamics of the One Dimensional Ising Model
We analyse the steady state regime of a one dimensional Ising model under a
tapping dynamics recently introduced by analogy with the dynamics of
mechanically perturbed granular media. The idea that the steady state regime
may be described by a flat measure over metastable states of fixed energy is
tested by comparing various steady state time averaged quantities in extensive
numerical simulations with the corresponding ensemble averages computed
analytically with this flat measure. The agreement between the two averages is
excellent in all the cases examined, showing that a static approach is capable
of predicting certain measurable properties of the steady state regime.Comment: 11 pages, 5 figure
Optimal Bell tests do not require maximally entangled states
Any Bell test consists of a sequence of measurements on a quantum state in
space-like separated regions. Thus, a state is better than others for a Bell
test when, for the optimal measurements and the same number of trials, the
probability of existence of a local model for the observed outcomes is smaller.
The maximization over states and measurements defines the optimal nonlocality
proof. Numerical results show that the required optimal state does not have to
be maximally entangled.Comment: 1 figure, REVTEX
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