776 research outputs found
Sudden death and sudden birth of entanglement in common structured reservoirs
We study the exact entanglement dynamics of two qubits in a common structured
reservoir. We demonstrate that, for certain classes of entangled states,
entanglement sudden death occurs, while for certain initially factorized
states, entanglement sudden birth takes place. The backaction of the
non-Markovian reservoir is responsible for revivals of entanglement after
sudden death has occurred, and also for periods of disentanglement following
entanglement sudden birth.Comment: 4 pages, 2 figure
Dynamics of quantum correlations in two-qubit systems within non-Markovian environments
Knowledge of the dynamical behavior of correlations with no classical
counterpart, like entanglement, nonlocal correlations and quantum discord, in
open quantum systems is of primary interest because of the possibility to
exploit these correlations for quantum information tasks. Here we review some
of the most recent results on the dynamics of correlations in bipartite systems
embedded in non-Markovian environments that, with their memory effects,
influence in a relevant way the system dynamics and appear to be more
fundamental than the Markovian ones for practical purposes. Firstly, we review
the phenomenon of entanglement revivals in a two-qubit system for both
independent environments and a common environment. We then consider the
dynamics of quantum discord in non-Markovian dephasing channel and briefly
discuss the occurrence of revivals of quantum correlations in classical
environments.Comment: 20 pages, 4 figures. Review article, in press in Int. J. Mod. Phys.
B, special issue "Classical Vs Quantum correlations in composite systems",
edited by L. Amico, S. Bose, V. Korepin and V. Vedra
Entanglement dynamics of two independent qubits in environments with and without memory
A procedure to obtain the dynamics of independent qudits (-level
systems) each interacting with its own reservoir, for any arbitrary initial
state, is presented. This is then applied to study the dynamics of the
entanglement of two qubits, initially in an extended Werner-like mixed state
with each of them in a zero temperature non-Markovian environment. The
dependence of the entanglement dynamics on the purity and degree of
entanglement of the initial states and on the amount of non-Markovianity is
also given. This extends the previous work about non-Markovian effects on the
two-qubit entanglement dynamics for initial Bell-like states [B. Bellomo
\textit{et al.}, Phys. Rev. Lett. \textbf{99}, 160502 (2007)]. The effect of
temperature on the two-qubit entanglement dynamics in a Markovian environment
is finally obtained.Comment: 10 pages, 6 figure
Coherence and Entanglement in Two-Qubit Dynamics: Interplay of the Induced Exchange Interaction and Quantum Noise due to Thermal Bosonic Environment
We present a review of our recent results for the comparative evaluation of
the induced exchange interaction and quantum noise mediated by the bosonic
environment in two-qubit systems. We report new calculations for
P-donor-electron spins in Si-Ge type materials. Challenges and open problems
are discussed.Comment: Invited Review, 17 pages in LaTeX, with 4 EPS figure
The Rotating-Wave Approximation: Consistency and Applicability from an Open Quantum System Analysis
We provide an in-depth and thorough treatment of the validity of the
rotating-wave approximation (RWA) in an open quantum system. We find that when
it is introduced after tracing out the environment, all timescales of the open
system are correctly reproduced, but the details of the quantum state may not
be. The RWA made before the trace is more problematic: it results in incorrect
values for environmentally-induced shifts to system frequencies, and the
resulting theory has no Markovian limit. We point out that great care must be
taken when coupling two open systems together under the RWA. Though the RWA can
yield a master equation of Lindblad form similar to what one might get in the
Markovian limit with white noise, the master equation for the two coupled
systems is not a simple combination of the master equation for each system, as
is possible in the Markovian limit. Such a naive combination yields inaccurate
dynamics. To obtain the correct master equation for the composite system a
proper consideration of the non-Markovian dynamics is required.Comment: 17 pages, 0 figures
Entanglement and Quantum Noise Due to a Thermal Bosonic Field
We analyze the indirect exchange interaction between two two-state systems,
e.g., spins 1/2, subject to a common finite-temperature environment modeled by
bosonic modes. The environmental modes, e.g., phonons or cavity photons, are
also a source of quantum noise. We analyze the coherent vs noise-induced
features of the two-spin dynamics and predict that for low enough temperatures
the induced interaction is coherent over time scales sufficient to create
entanglement. A nonperturbative approach is utilized to obtain an exact
solution for the onset of the induced interaction, whereas for large times, a
Markovian scheme is used. We identify the time scales for which the spins
develop entanglement for various spatial separations. For large enough times,
the initially created entanglement is erased by quantum noise. Estimates for
the interaction and the level of quantum noise for localized impurity electron
spins in Si-Ge type semiconductors are given.Comment: 12 pages, 9 figures; typos correcte
A non-Markovian optical signature for detecting entanglement in coupled excitonic qubits
We identify an optical signature for detecting entanglement in experimental
nanostructure systems comprising coupled excitonic qubits. This signature owes
its strength to non-Markovian dynamical effects in the second-order temporal
coherence function of the emitted radiation. We calculate autocorrelation and
cross-correlation functions for both selective and collective light excitation,
and prove that the coherence properties of the emitted light do indeed carry
information about the entanglement of the initial multi-qubit state.
We also show that this signature can survive in the presence of a noisy
environment.Comment: 4 pages, 4 color figures. Minor changes. Accepted version to be
published in Europhysics Letter
Non-Markovian entanglement dynamics of quantum continuous variable systems in thermal environments
We study two continuous variable systems (or two harmonic oscillators) and
investigate their entanglement evolution under the influence of non-Markovian
thermal environments. The continuous variable systems could be two modes of
electromagnetic fields or two nanomechanical oscillators in the quantum domain.
We use quantum open system method to derive the non-Markovian master equations
of the reduced density matrix for two different but related models of the
continuous variable systems. The two models both consist of two interacting
harmonic oscillators. In model A, each of the two oscillators is coupled to its
own independent thermal reservoir, while in model B the two oscillators are
coupled to a common reservoir. To quantify the degrees of entanglement for the
bipartite continuous variable systems in Gaussian states, logarithmic
negativity is used. We find that the dynamics of the quantum entanglement is
sensitive to the initial states, the oscillator-oscillator interaction, the
oscillator-environment interaction and the coupling to a common bath or to
different, independent baths.Comment: 10 two-column pages, 8 figures, to appear in Phys. Rev.
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