3,473 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
Entanglement degradation in the solid state: interplay of adiabatic and quantum noise
We study entanglement degradation of two non-interacting qubits subject to
independent baths with broadband spectra typical of solid state nanodevices. We
obtain the analytic form of the concurrence in the presence of adiabatic noise
for classes of entangled initial states presently achievable in experiments. We
find that adiabatic (low frequency) noise affects entanglement reduction
analogously to pure dephasing noise. Due to quantum (high frequency) noise,
entanglement is totally lost in a state-dependent finite time. The possibility
to implement on-chip both local and entangling operations is briefly discussed.Comment: Replaced with published version. Minor change
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.
Dynamics of correlations due to a phase noisy laser
We analyze the dynamics of various kinds of correlations present between two
initially entangled independent qubits, each one subject to a local phase noisy
laser. We give explicit expressions of the relevant quantifiers of correlations
for the general case of single-qubit unital evolution, which includes the case
of a phase noisy laser. Although the light field is treated as classical, we
find that this model can describe revivals of quantum correlations. Two
different dynamical regimes of decay of correlations occur, a Markovian one
(exponential decay) and a non-Markovian one (oscillatory decay with revivals)
depending on the values of system parameters. In particular, in the
non-Markovian regime, quantum correlations quantified by quantum discord show
an oscillatory decay faster than that of classical correlations. Moreover,
there are time regions where nonzero discord is present while entanglement is
zero.Comment: 7 pages, 3 figures, accepted for publication in Phys. Scripta,
special issue for CEWQO 2011 proceeding
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
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
Gravitational Collapse of a Shell of Quantized Matter
The semi-classical collapse, including lowest order back-reaction, of a thin
shell of self-gravitating quantized matter is illustrated. The conditions for
which self-gravitating matter forms a thin shell are first discussed and an
effective Lagrangian for such matter is obtained. The matter-gravity system is
then quantized, the semi-classical limit for gravitation is taken and the
method of adiabatic invariants is applied to the resulting time dependent
matter Hamiltonian. The governing equations are integrated numerically, for
suitable initial conditions, in order to illustrate the effect of
back-reaction, due to the creation of matter, in slowing down the collapse near
the horizon.Comment: 20 pages, 1 eps figure. Problem with figure fixe
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