170 research outputs found
To freeze or not to: Quantum correlations under local decoherence
We provide necessary and sufficient conditions for freezing of quantum
correlations as measured by quantum discord and quantum work deficit in the
case of bipartite as well as multipartite states subjected to local noisy
channels. We recognize that inhomogeneity of the magnetizations of the shared
quantum states plays an important role in the freezing phenomena. We show that
the frozen value of the quantum correlation and the time interval for freezing
follow a complementarity relation. For states which do not exhibit "exact"
freezing, but can be frozen "effectively", by having a very slow decay rate
with suitable tuning of the state parameters, we introduce an index -- the
freezing index -- to quantify the goodness of freezing. We find that the
freezing index can be used to detect quantum phase transitions and discuss the
corresponding scaling behavior.Comment: 14 pages, 9 figures, close to published version, title changed by
Phys. Rev. A. to 'Freezing of quantum correlations under local decoherence
Mutual Composite Fermion and composite Boson approaches to balanced and imbalanced bilayer quantum Hall system: an electronic analogy of the Helium 4 system
We use both Mutual Composite Fermion (MCF) and Composite Boson (CB) approach
to study balanced and im-balanced Bi-Layer Quantum Hall systems (BLQH) and make
critical comparisons between the two approaches. We find the CB approach is
superior to the MCF approach in studying ground states with different kinds of
broken symmetries. In the phase representation of the CB theory, we first study
the Excitonic superfluid state (ESF). The theory puts spin and charge degree
freedoms in the same footing, explicitly bring out the spin-charge connection
and classify all the possible excitations in a systematic way. Then in the dual
density representation of the CB theory, we study possible intermediate phases
as the distance increases. We propose there are two critical distances and three phases as the distance increases. When ,
the system is in the ESF state which breaks the internal symmetry,
when , the system is in an Pseudo-spin density wave
(PSDW) state which breaks the translational symmetry, there is a first order
transition at driven by the collapsing of magneto-roton minimum at a
finite wavevector in the pseudo-spin channel. When , the
system becomes two weakly coupled Composite Fermion Fermi Liquid
(FL) state. There is also a first order transition at . We
construct a quantum Ginzburg Landau action to describe the transition from ESF
to PSDW which break the two completely different symmetries. By using the QGL
action, we explicitly show that the PSDW takes a square lattice and analyze in
detail the properties of the PSDW at zero and finite temperature.Comment: 29 PRB pages, 18 figures, 2 tables, REVTEX
Nonperturbative Quantum Gravity
Asymptotic safety describes a scenario in which general relativity can be
quantized as a conventional field theory, despite being nonrenormalizable when
expanding it around a fixed background geometry. It is formulated in the
framework of the Wilsonian renormalization group and relies crucially on the
existence of an ultraviolet fixed point, for which evidence has been found
using renormalization group equations in the continuum.
"Causal Dynamical Triangulations" (CDT) is a concrete research program to
obtain a nonperturbative quantum field theory of gravity via a lattice
regularization, and represented as a sum over spacetime histories. In the
Wilsonian spirit one can use this formulation to try to locate fixed points of
the lattice theory and thereby provide independent, nonperturbative evidence
for the existence of a UV fixed point.
We describe the formalism of CDT, its phase diagram, possible fixed points
and the "quantum geometries" which emerge in the different phases. We also
argue that the formalism may be able to describe a more general class of
Ho\v{r}ava-Lifshitz gravitational models.Comment: Review, 146 pages, many figure
The classical-quantum boundary for correlations: discord and related measures
One of the best signatures of nonclassicality in a quantum system is the
existence of correlations that have no classical counterpart. Different methods
for quantifying the quantum and classical parts of correlations are amongst the
more actively-studied topics of quantum information theory over the past
decade. Entanglement is the most prominent of these correlations, but in many
cases unentangled states exhibit nonclassical behavior too. Thus distinguishing
quantum correlations other than entanglement provides a better division between
the quantum and classical worlds, especially when considering mixed states.
Here we review different notions of classical and quantum correlations
quantified by quantum discord and other related measures. In the first half, we
review the mathematical properties of the measures of quantum correlations,
relate them to each other, and discuss the classical-quantum division that is
common among them. In the second half, we show that the measures identify and
quantify the deviation from classicality in various
quantum-information-processing tasks, quantum thermodynamics, open-system
dynamics, and many-body physics. We show that in many cases quantum
correlations indicate an advantage of quantum methods over classical ones.Comment: Close to the published versio
- …