143 research outputs found
Biases on cosmological parameters by general relativity effects
General relativistic corrections to the galaxy power spectrum appearing at
the horizon scale, if neglected, may induce biases on the measured values of
the cosmological parameters. In this paper, we study the impact of general
relativistic effects on non standard cosmologies such as scenarios with a time
dependent dark energy equation of state, with a coupling between the dark
energy and the dark matter fluids or with non-Gaussianities. We then explore
whether general relativistic corrections affect future constraints on
cosmological parameters in the case of a constant dark energy equation of state
and of non-Gaussianities. We find that relativistic corrections on the power
spectrum are not expected to affect the foreseen errors on the cosmological
parameters nor to induce large biases on them.Comment: 17 pages, 5 figures, one added figure, results of Tab. I revised,
version accepted for publication in PR
Spotlighting quantum critical points via quantum correlations at finite temperatures
We extend the program initiated in [T. Werlang et al., Phys. Rev. Lett. 105,
095702 (2010)] in several directions. Firstly, we investigate how useful
quantum correlations, such as entanglement and quantum discord, are in the
detection of critical points of quantum phase transitions when the system is at
finite temperatures. For that purpose we study several thermalized spin models
in the thermodynamic limit, namely, the XXZ model, the XY model, and the Ising
model, all of which with an external magnetic field. We compare the ability of
quantum discord, entanglement, and some thermodynamic quantities to spotlight
the quantum critical points for several different temperatures. Secondly, for
some models we go beyond nearest-neighbors and also study the behavior of
entanglement and quantum discord for second nearest-neighbors around the
critical point at finite temperature. Finally, we furnish a more quantitative
description of how good all these quantities are in spotlighting critical
points of quantum phase transitions at finite T, bridging the gap between
experimental data and those theoretical descriptions solely based on the
unattainable absolute zero assumption.Comment: 11 pages, 12 figures, RevTex4-1; v2: published versio
Quantum correlations in a few-atom spin-1 Bose-Hubbard model
We study the thermal quantum correlations and entanglement in spin-1 Bose-Hubbard model with two and three particles. While we use negativity to calculate entanglement, more general non-classical correlations are quantified using a new measure based on a necessary and sufficient condition for zero-discord state. We demonstrate that the energy level crossings in the ground state of the system are signalled by both the behavior of thermal quantum correlations and entanglement
Probabilistic teleportation of unknown two-particle state via POVM
We propose a scheme for probabilistic teleportation of unknown two-particle
state with partly entangled four-particle state via POVM. In this scheme the
teleportation of unknown two-particle state can be realized with certain
probability by performing two Bell state measurements, a proper POVM and a
unitary transformation.Comment: 5 pages, no figur
Phenomenology of symmetry breaking from extra dimensions
Motivated by the electroweak hierarchy problem, we consider theories with two
extra dimensions in which the four-dimensional scalar fields are components of
gauge boson in full space. We explore the Nielsen-Olesen instability for SU(N)
on a torus, in the presence of a magnetic background. A field theory approach
is developed, computing explicitly the minimum of the complete effective
potential, including tri-linear and quartic couplings and determining the
symmetries of the stable vacua. We also develop appropriate gauge-fixing terms
when both Kaluza-Klein and Landau levels are present and interacting,
discussing the interplay between the possible six and four dimensional choices.
The equivalence between coordinate dependent and constant Scherk-Schwarz
boundary conditions -associated to either continuous or discrete Wilson lines-
is analyzed.Comment: 39 pages and 8 eps figures. Few changes in section
Multi-Receiver Quantum Dense Coding with Non-Symmetric Quantum Channel
A two-receiver quantum dense coding scheme and an -receiver quantum dense
coding scheme, in the case of non-symmetric Hilbert spaces of the particles of
the quantum channel, are investigated in this paper. A sender can send his
messages to many receivers simultaneously. The scheme can be applied to quantum
secret sharing and controlled quantum dense coding.Comment: To appear in Journal of the Korean Physical Societ
The controlled teleportation of an arbitrary two-atom entangled state in driven cavity QED
In this paper, we propose a scheme for the controlled teleportation of an
arbitrary two-atom entangled state
in driven cavity QED.
An arbitrary two-atom entangled state can be teleported perfectly with the help
of the cooperation of the third side by constructing a three-atom GHZ entangled
state as the controlled channel. This scheme does not involve apparent (or
direct) Bell-state measurement and is insensitive to the cavity decay and the
thermal field. The probability of the success in our scheme is 1.0.Comment: 10 page
Entanglement study of the 1D Ising model with Added Dzyaloshinsky-Moriya interaction
We have studied occurrence of quantum phase transition in the one-dimensional
spin-1/2 Ising model with added Dzyaloshinsky-Moriya (DM) interaction from bi-
partite and multi-partite entanglement point of view. Using exact numerical
solutions, we are able to study such systems up to 24 qubits. The minimum of
the entanglement ratio R \tau 2/\tau 1 < 1, as a novel estimator of
QPT, has been used to detect QPT and our calculations have shown that its
minimum took place at the critical point. We have also shown both the
global-entanglement (GE) and multipartite entanglement (ME) are maximal at the
critical point for the Ising chain with added DM interaction. Using matrix
product state approach, we have calculated the tangle and concurrence of the
model and it is able to capture and confirm our numerical experiment result.
Lack of inversion symmetry in the presence of DM interaction stimulated us to
study entanglement of three qubits in symmetric and antisymmetric way which
brings some surprising results.Comment: 18 pages, 9 figures, submitte
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