75 research outputs found
On the phase transition of light in cavity QED lattices
Systems of strongly interacting atoms and photons, that can be realized
wiring up individual cavity QED systems into lattices, are perceived as a new
platform for quantum simulation. While sharing important properties with other
systems of interacting quantum particles here we argue that the nature of
light-matter interaction gives rise to unique features with no analogs in
condensed matter or atomic physics setups. By discussing the physics of a
lattice model of delocalized photons coupled locally with two-level systems
through the elementary light-matter interaction described by the Rabi model, we
argue that the inclusion of counter rotating terms, so far neglected, is
crucial to stabilize finite-density quantum phases of correlated photons out of
the vacuum, with no need for an artificially engineered chemical potential. We
show that the competition between photon delocalization and Rabi non-linearity
drives the system across a novel parity symmetry-breaking quantum
criticality between two gapped phases which shares similarities with the Dicke
transition of quantum optics and the Ising critical point of quantum magnetism.
We discuss the phase diagram as well as the low-energy excitation spectrum and
present analytic estimates for critical quantities.Comment: 5+3 pages, published versio
Quantum entanglement of spin-1 bosons with coupled ground states in optical lattices
We examine particle entanglement, characterized by pseudo-spin squeezing, of
spin-1 bosonic atoms with coupled ground states in a one-dimensional optical
lattice. Both the superfluid and Mott-insulator phases are investigated
separately for ferromagnetic and antiferromagnetic interactions. Mode
entanglement is also discussed in the Mott insulating phase. The role of a
small but nonzero angle between the polarization vectors of counter-propagating
lasers forming the optical lattice on quantum correlations is investigated as
well.Comment: 18 pages, 8 figures. To be published in Journal of Physics
Quantum correlations of spin-1 atoms in an optical lattice
In this work, we investigate the system of cold spin-1 atoms in a one dimensional optical lattice in relation with squeezing and entanglement. By using the corresponding Bose-Hubbard Hamiltonian, both superfluid and Mott-insulator phases are studied by using numerical methods in the mean-field approximation. To observe the presence of entanglement, we used a squeezing measure as a criterion for quantum correlations. We further investigate the two interaction regimes, namely ferromagnetic and antiferromagnetic in the case of zero and nonzero but very small angle between the counterpropagating laser beams that form the optical lattice. States in the superfluid phase are calculated analytically by using the perturbation theory. © 2009 Pleiades Publishing, Ltd
Protein folding rates correlate with heterogeneity of folding mechanism
By observing trends in the folding kinetics of experimental 2-state proteins
at their transition midpoints, and by observing trends in the barrier heights
of numerous simulations of coarse grained, C-alpha model, Go proteins, we show
that folding rates correlate with the degree of heterogeneity in the formation
of native contacts. Statistically significant correlations are observed between
folding rates and measures of heterogeneity inherent in the native topology, as
well as between rates and the variance in the distribution of either
experimentally measured or simulated phi-values.Comment: 11 pages, 3 figures, 1 tabl
Spin squeezing and entanglement
We reformulate definition of spin squeezing and spin coherence in terms of the total variance in spin operators. We propose a new measure of spin squeezing. We show equivalence of spin squeezing and spin entanglement. © 2007 Optical Society of America
Entanglement and its operational measure
An operational representation of concurrence measuring the entanglement of bipartite systems by means of averages of basic observables is discussed. We prove the validity of this representation for bipartite systems with any dimension of a single-party Hilbert space. We show that Wigner-Yanase "skew" information gives a reasonable estimation of the amount of entanglement (in ebits) carried by mixed two-qubit states. ©2006 Springer Science+Business Media, Inc
Quantifying quantum information via uncertainties
We show, for a state ψ of a quantum system with the dynamic symmetry given by the Lie group G, total amount of quantum information and entanglement is provided by summarized uncertainty of basic observables. © 2007 Optical Society of America
Entanglement of qutrits
For two types of qutrits specified by the dynamical symmetry SU(3) and SU(2), we consider the difference in entanglement caused by the lack of quantum observables in the latter case. In particular, we show that the SU(2) qutrits can have specific separable entanglement caused by quantum correlations of intrinsic degrees of freedom in a single party without interparty correlations. © Nauka/Interperiodica 2007
Quantum correlations among superradiant bose-einstein condensate atoms
Quantum correlations among atoms in superradiant Bose-Einstein condensates are discussed. It is shown that atoms in the superradiant atomic condensate can exhibit continuous variable quantum entanglement analogous to Einstein-Podolsky-Rosen (EPR)-type quantum correlations. Comparison to quantum entanglement in the Dicke model in thermal equilibrium is provided. Copyright © 2010 Pleiades Publishing, Ltd
Raman superradiance and spin lattice of ultracold atoms in optical cavities
We investigate synthesis of a hyperfine spin lattice in an atomic
Bose-Einstein condensate, with two hyperfine spin components, inside a
one-dimensional high-finesse optical cavity, using off-resonant superradiant
Raman scattering. Spatio-temporal evolution of the relative population of the
hyperfine spin modes is examined numerically by solving the coupled
cavity-condensate mean field equations in the dispersive regime. We find,
analytically and numerically, that beyond a certain threshold of the transverse
laser pump, Raman superradiance and self-organization of the hyperfine spin
components simultaneously occur and as a result a magnetic lattice is formed.
The effects of an extra laser pump parallel to the cavity axis and the
time-dependence of the pump strength on the synthesis of a sharper lattice are
also addressed.Comment: Accepted for publication in New Journal of Physics. 16 pages and 6
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