39 research outputs found
Transverse Ising Model: Markovian evolution of classical and quantum correlations under decoherence
The transverse Ising Model (TIM) in one dimension is the simplest model which
exhibits a quantum phase transition (QPT). Quantities related to quantum
information theoretic measures like entanglement, quantum discord (QD) and
fidelity are known to provide signatures of QPTs. The issue is less well
explored when the quantum system is subjected to decoherence due to its
interaction, represented by a quantum channel, with an environment. In this
paper we study the dynamics of the mutual information , the
classical correlations and the quantum correlations
, as measured by the QD, in a two-qubit state the density matrix
of which is the reduced density matrix obtained from the ground state of the
TIM in 1d. The time evolution brought about by system-environment interactions
is assumed to be Markovian in nature and the quantum channels considered are
amplitude damping, bit-flip, phase-flip and bit-phase-flip. Each quantum
channel is shown to be distinguished by a specific type of dynamics. In the
case of the phase-flip channel, there is a finite time interval in which the
quantum correlations are larger in magnitude than the classical correlations.
For this channel as well as the bit-phase-flip channel, appropriate quantities
associated with the dynamics of the correlations can be derived which signal
the occurrence of a QPT.Comment: 8 pages, 7 figures, revtex4-1, version accepted for publication in
Eur. Phys. J.
Quantum circuits for spin and flavor degrees of freedom of quarks forming nucleons
We discuss the quantum-circuit realization of the state of a nucleon in the
scope of simple symmetry groups. Explicit algorithms are presented for the
preparation of the state of a neutron or a proton as resulting from the
composition of their quark constituents. We estimate the computational
resources required for such a simulation and design a photonic network for its
implementation. Moreover, we highlight that current work on three-body
interactions in lattices of interacting qubits, combined with the
measurement-based paradigm for quantum information processing, may also be
suitable for the implementation of these nucleonic spin states.Comment: 5 pages, 2 figures, RevTeX4; Accepted for publication in Quantum
Information Processin
Quantum discord evolution of three-qubit states under noisy channels
We investigated the dissipative dynamics of quantum discord for correlated
qubits under Markovian environments.
The basic idea in the present scheme is that quantum discord is more general,
and possibly more robust and fundamental, than entanglement. We provide three
initially correlated qubits in pure Greenberger-Horne-Zeilinger (GHZ) or W
state and analyse the time evolution of the quantum discord under various
dissipative channels such as:
Pauli channels , , and , as well as
depolarising channels. Surprisingly, we find that under the action of Pauli
channel , the quantum discord of GHZ state is not affected by
decoherence. For the remaining dissipative channels, the W state is more robust
than the GHZ state against decoherence. Moreover, we compare the dynamics of
entanglement with that of the quantum discord under the conditions in which
disentanglement occurs and show that quantum discord is more robust than
entanglement except for phase flip coupling of the three qubits system to the
environment.Comment: 17 pages, 4 figures, accepted for publication in EPJ
Quantum Correlation in One-dimensional Extend Quantum Compass Model
We study the correlations in the one-dimensional extended quantum compass
model in a transverse magnetic field. By exactly solving the Hamiltonian, we
find that the quantum correlation of the ground state of one-dimensional
quantum compass model is vanishing. We show that quantum discord can not only
locate the quantum critical points, but also discern the orders of phase
transitions. Furthermore, entanglement quantified by concurrence is also
compared.Comment: 8 pages, 14 figures, to appear in Eur. Phys. J.
Digital Quantum Simulation with Rydberg Atoms
We discuss in detail the implementation of an open-system quantum simulator
with Rydberg states of neutral atoms held in an optical lattice. Our scheme
allows one to realize both coherent as well as dissipative dynamics of complex
spin models involving many-body interactions and constraints. The central
building block of the simulation scheme is constituted by a mesoscopic Rydberg
gate that permits the entanglement of several atoms in an efficient, robust and
quick protocol. In addition, optical pumping on ancillary atoms provides the
dissipative ingredient for engineering the coupling between the system and a
tailored environment. As an illustration, we discuss how the simulator enables
the simulation of coherent evolution of quantum spin models such as the
two-dimensional Heisenberg model and Kitaev's toric code, which involves
four-body spin interactions. We moreover show that in principle also the
simulation of lattice fermions can be achieved. As an example for controlled
dissipative dynamics, we discuss ground state cooling of frustration-free spin
Hamiltonians.Comment: submitted to special issue "Quantum Information with Neutral
Particles" of "Quantum Information Processing
Quantum optics in the phase space - A tutorial on Gaussian states
In this tutorial, we introduce the basic concepts and mathematical tools
needed for phase-space description of a very common class of states, whose
phase properties are described by Gaussian Wigner functions: the Gaussian
states. In particular, we address their manipulation, evolution and
characterization in view of their application to quantum information.Comment: Tutorial. 23 pages, 1 figure. Updated version accepted for
publication in EPJ - ST devoted to the memory of Federico Casagrand
Dynamics of multipartite quantum correlations under decoherence
Quantum discord is an optimal resource for the quantification of classical
and non-classical correlations as compared to other related measures. Geometric
measure of quantum discord is another measure of quantum correlations.
Recently, the geometric quantum discord for multipartite states has been
introduced by Jianwei Xu [arxiv:quant/ph.1205.0330]. Motivated from the recent
study [Ann. Phys. 327 (2012) 851] for the bipartite systems, I have
investigated global quantum discord (QD) and geometric quantum discord (GQD)
under the influence of external environments for different multipartite states.
Werner-GHZ type three-qubit and six-qubit states are considered in inertial and
non-inertial settings. The dynamics of QD and GQD is investigated under
amplitude damping, phase damping, depolarizing and flipping channels. It is
seen that the quantum discord vanishes for p>0.75 in case of three-qubit GHZ
states and for p>0.5 for six qubit GHZ states. This implies that multipartite
states are more fragile to decoherence for higher values of N. Surprisingly, a
rapid sudden death of discord occurs in case of phase flip channel. However,
for bit flip channel, no sudden death happens for the six-qubit states. On the
other hand, depolarizing channel heavily influences the QD and GQD as compared
to the amplitude damping channel. It means that the depolarizing channel has
the most destructive influence on the discords for multipartite states. From
the perspective of accelerated observers, it is seen that effect of environment
on QD and GQD is much stronger than that of the acceleration of non-inertial
frames. The degradation of QD and GQD happens due to Unruh effect. Furthermore,
QD exhibits more robustness than GQD when the multipartite systems are exposed
to environment.Comment: 15 pages, 4 figures, 4 table
Various correlations in a Heisenberg XXZ spin chain both in thermal equilibrium and under the intrinsic decoherence
In this paper we discuss various correlations measured by the concurrence
(C), classical correlation (CC), quantum discord (QD), and geometric measure of
discord (GMD) in a two-qubit Heisenberg XXZ spin chain in the presence of
external magnetic field and Dzyaloshinskii-Moriya (DM) anisotropic
antisymmetric interaction. Based on the analytically derived expressions for
the correlations for the cases of thermal equilibrium and the inclusion of
intrinsic decoherence, we discuss and compare the effects of various system
parameters on the correlations in different cases. The results show that the
anisotropy Jz is considerably crucial for the correlations in thermal
equilibrium at zero temperature limit but ineffective under the consideration
of the intrinsic decoherence, and these quantities decrease as temperature T
rises on the whole. Besides, J turned out to be constructive, but B be
detrimental in the manipulation and control of various quantities both in
thermal equilibrium and under the intrinsic decoherence which can be avoided by
tuning other system parameters, while D is constructive in thermal equilibrium,
but destructive in the case of intrinsic decoherence in general. In addition,
for the initial state , all
the correlations except the CC, exhibit a damping oscillation to a stable value
larger than zero following the time, while for the initial state , all the correlations monotonously
decrease, but CC still remains maximum. Moreover, there is not a definite
ordering of these quantities in thermal equilibrium, whereas there is a
descending order of the CC, C, GMD and QD under the intrinsic decoherence with
a nonnull B when the initial state is .Comment: 8 pages, 7 figure
Development and application of efficient methods for the forward propagation of epistemic uncertainty and sensitivity analysis within complex broad-scale flood risk system models
Increasingly, an understanding of flood risk across regions and nations, and an ability to explore how these might change in time, is seen as a prerequisite to effective and efficient flood risk management. In response, specific flood risk analysis methods have been developed that are both accurate and fast to run. Although widely acknowledged as desirable, it has not previously been possible to quantify the uncertainty associated with the assessed flood probability, consequence, or risk. To help overcome this deficiency, an efficient method for the propagation of epistemic uncertainties through large-scale flood risk system models has been developed and trialed for three pilot catchments. The approach is allied to an efficient sensitivity analysis that enables the influence of individual uncertainties on the output quantity of risk to be isolated, enabling future research, development, and data-gathering efforts to be focused
Complementarity in variable strength quantum non-demolition measurements
International audienceUsing a linear optic quantum gate we perform a variable strength quantum non-demolition measurement, to elucidate the role of which-path knowledge in a complementarity experiment. Specifically, we demonstrate that the entanglement created by the measurement interaction prevents an exhaustive description in terms of complementary wave-like and particle-like behaviour of a single photon in an interferometer