4,095 research outputs found
Quantum synchronization as a local signature of super- and subradiance
We study the relationship between the collective phenomena of super and
subradiance and spontaneous synchronization of quantum systems. To this aim we
revisit the case of two detuned qubits interacting through a pure dissipative
bosonic environment, which contains the minimal ingredients for our analysis.
By using the Liouville formalism, we are able to find analytically the ultimate
connection between these phenomena. We find that dynamical synchronization is
due to the presence of long standing coherence between the ground state of the
system and the subradiant state. We finally show that, under pure dissipation,
the emergence of spontaneous synchronization and of subradiant emission occur
on the same time scale. This reciprocity is broken in the presence of dephasing
noise.Comment: 12 pages, 6 figure
Dispersion of Klauder's temporally stable coherent states for the hydrogen atom
We study the dispersion of the "temporally stable" coherent states for the
hydrogen atom introduced by Klauder. These are states which under temporal
evolution by the hydrogen atom Hamiltonian retain their coherence properties.
We show that in the hydrogen atom such wave packets do not move
quasi-classically; i.e., they do not follow with no or little dispersion the
Keplerian orbits of the classical electron. The poor quantum-classical
correspondence does not improve in the semiclassical limit.Comment: 6 pages, 2 figure
Dynamics of Entanglement and Bell-nonlocality for Two Stochastic Qubits with Dipole-Dipole Interaction
We have studied the analytical dynamics of Bell nonlocality as measured by
CHSH inequality and entanglement as measured by concurrence for two noisy
qubits that have dipole-dipole interaction. The nonlocal entanglement created
by the dipole-dipole interaction is found to be protected from sudden death for
certain initial states
Revival of quantum correlations without system-environment back-action
Revivals of quantum correlations have often been explained in terms of
back-action on quantum systems by their quantum environment(s). Here we
consider a system of two independently evolving qubits, each locally
interacting with a classical random external field. The environments of the
qubits are also independent, and there is no back-action on the qubits.
Nevertheless, entanglement, quantum discord and classical correlations between
the two qubits may revive in this model. We explain the revivals in terms of
correlations in a classical-quantum state of the environments and the qubits.
Although classical states cannot store entanglement on their own, they can play
a role in storing and reviving entanglement. It is important to know how the
absence of back-action, or modelling an environment as classical, affects the
kind of system time evolutions one is able to describe. We find a class of
global time evolutions where back-action is absent and for which there is no
loss of generality in modelling the environment as classical. Finally, we show
that the revivals can be connected with the increase of a parameter used to
quantify non-Markovianity of the single-qubit dynamics.Comment: 8 pages, 4 figures; this version to appear in Phys. Rev.
Classical Evolution of Quantum Elliptic States
The hydrogen atom in weak external fields is a very accurate model for the
multiphoton excitation of ultrastable high angular momentum Rydberg states, a
process which classical mechanics describes with astonishing precision. In this
paper we show that the simplest treatment of the intramanifold dynamics of a
hydrogenic electron in external fields is based on the elliptic states of the
hydrogen atom, i.e., the coherent states of SO(4), which is the dynamical
symmetry group of the Kepler problem. Moreover, we also show that classical
perturbation theory yields the {\it exact} evolution in time of these quantum
states, and so we explain the surprising match between purely classical
perturbative calculations and experiments. Finally, as a first application, we
propose a fast method for the excitation of circular states; these are
ultrastable hydrogenic eigenstates which have maximum total angular momentum
and also maximum projection of the angular momentum along a fixed direction. %Comment: 8 Pages, 2 Figures. Accepted for publication in Phys. Rev.
Entanglement Dynamics of Two Independent Cavity-Embedded Quantum Dots
We investigate the dynamical behavior of entanglement in a system made by two
solid-state emitters, as two quantum dots, embedded in two separated
micro-cavities. In these solid-state systems, in addition to the coupling with
the cavity mode, the emitter is coupled to a continuum of leaky modes providing
additional losses and it is also subject to a phonon-induced pure dephasing
mechanism. We model this physical configuration as a multipartite system
composed by two independent parts each containing a qubit embedded in a
single-mode cavity, exposed to cavity losses, spontaneous emission and pure
dephasing. We study the time evolution of entanglement of this multipartite
open system finally applying this theoretical framework to the case of
currently available solid-state quantum dots in micro-cavities.Comment: 10 pages, 4 figures, to appear in Topical Issue of Physica Scripta on
proceedings of CEWQO 201
Tripartite entanglement dynamics in a system of strongly driven qubits
We study the dynamics of tripartite entanglement in a system of two strongly
driven qubits individually coupled to a dissipative cavity. We aim at
explanation of the previously noted entanglement revival between two qubits in
this system. We show that the periods of entanglement loss correspond to the
strong tripartite entanglement between the qubits and the cavity and the
recovery has to do with an inverse process. We demonstrate that the overall
process of qubit-qubit entanglement loss is due to the second order coupling to
the external continuum which explains the exp[-g^2 t/2+g^2 k t^3/6+\cdot] for
of the entanglement loss reported previously.Comment: 9 pages, 5 figure
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
Temporally stable coherent states in energy degenerate systems: The hydrogen atom
Klauder's recent generalization of the harmonic oscillator coherent states
[J. Phys. A 29, L293 (1996)] is applicable only in non-degenerate systems,
requiring some additional structure if applied to systems with degeneracies.
The author suggests how this structure could be added, and applies the complete
method to the hydrogen atom problem. To illustrate how a certain degree of
freedom in the construction may be exercised, states are constructed which are
initially localized and evolve semi-classically, and whose long time evolution
exhibits "fractional revivals."Comment: 9 pages, 3 figure
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