791 research outputs found
Universal and deterministic manipulation of the quantum state of harmonic oscillators: a route to unitary gates for Fock State qubits
We present a simple quantum circuit that allows for the universal and
deterministic manipulation of the quantum state of confined harmonic
oscillators. The scheme is based on the selective interactions of the referred
oscillator with an auxiliary three-level system and a classical external
driving source, and enables any unitary operations on Fock states, two-by-two.
One circuit is equivalent to a single qubit unitary logical gate on Fock states
qubits. Sequences of similar protocols allow for complete, deterministic and
state-independent manipulation of the harmonic oscillator quantum state.Comment: 4 pages, 4 figure
Direct measurement of finite-time disentanglement induced by a reservoir
We propose a method for directly probing the dynamics of disentanglement of
an initial two-qubit entangled state, under the action of a reservoir. We show
that it is possible to detect disentanglement, for experimentally realizable
examples of decaying systems, through the measurement of a single observable,
which is invariant throughout the decay. The systems under consideration may
lead to either finite-time or asymptotic disentanglement. A general
prescription for measuring this observable, which yields an operational meaning
to entanglement measures, is proposed, and exemplified for cavity quantum
electrodynamics and trapped ions.Comment: 4 pages, 2 figure
Geometric phase induced by a cyclically evolving squeezed vacuum reservoir
We propose a new way to generate an observable geometric phase by means of a
completely incoherent phenomenon. We show how to imprint a geometric phase to a
system by "adiabatically" manipulating the environment with which it interacts.
As a specific scheme we analyse a multilevel atom interacting with a broad-band
squeezed vacuum bosonic bath. As the squeezing parameters are smoothly changed
in time along a closed loop, the ground state of the system acquires a
geometric phase. We propose also a scheme to measure such geometric phase by
means of a suitable polarization detection.Comment: 4 pages, 1 figur
Spin-1/2 geometric phase driven by decohering quantum fields
We calculate the geometric phase of a spin-1/2 system driven by a one and two
mode quantum field subject to decoherence. Using the quantum jump approach, we
show that the corrections to the phase in the no-jump trajectory are different
when considering an adiabatic and non-adiabatic evolution. We discuss the
implications of our results from both the fundamental as well as quantum
computational perspective.Comment: 4 page
Abrupt Changes in the Dynamics of Quantum Disentanglement
Entanglement evolution in high dimensional bipartite systems under
dissipation is studied. Discontinuities for the time derivative of the lower
bound of entanglement of formation is found depending on the initial conditions
for entangled states. This abrupt changes along the evolution appears as
precursors of entanglement sudden death.Comment: 4 pages and 6 figures, submitted for publicatio
Coherent evolution via reservoir driven holonomy
We show that in the limit of strongly interacting environment a system
initially prepared in a Decoherence Free Subspace (DFS) coherently evolves in
time, adiabatically following the changes of the DFS. If the reservoir cyclicly
evolves in time, the DFS states acquire an holonomy.Comment: 4 page
Controlling the dynamics of a coupled atom-cavity system by pure dephasing : basics and potential applications in nanophotonics
The influence of pure dephasing on the dynamics of the coupling between a
two-level atom and a cavity mode is systematically addressed. We have derived
an effective atom-cavity coupling rate that is shown to be a key parameter in
the physics of the problem, allowing to generalize the known expression for the
Purcell factor to the case of broad emitters, and to define strategies to
optimize the performances of broad emitters-based single photon sources.
Moreover, pure dephasing is shown to be able to restore lasing in presence of
detuning, a further demonstration that decoherence can be seen as a fundamental
resource in solid-state cavity quantum electrodynamics, offering appealing
perspectives in the context of advanced nano-photonic devices.Comment: 10 pages, 7 figure
Equilibrium and Disorder-induced behavior in Quantum Light-Matter Systems
We analyze equilibrium properties of coupled-doped cavities described by the
Jaynes-Cummings- Hubbard Hamiltonian. In particular, we characterize the
entanglement of the system in relation to the insulating-superfluid phase
transition. We point out the existence of a crossover inside the superfluid
phase of the system when the excitations change from polaritonic to purely
photonic. Using an ensemble statistical approach for small systems and
stochastic-mean-field theory for large systems we analyze static disorder of
the characteristic parameters of the system and explore the ground state
induced statistics. We report on a variety of glassy phases deriving from the
hybrid statistics of the system. On-site strong disorder induces insulating
behavior through two different mechanisms. For disorder in the light-matter
detuning, low energy cavities dominate the statistics allowing the excitations
to localize and bunch in such cavities. In the case of disorder in the light-
matter coupling, sites with strong coupling between light and matter become
very significant, which enhances the Mott-like insulating behavior. Inter-site
(hopping) disorder induces fluidity and the dominant sites are strongly coupled
to each other.Comment: about 10 pages, 12 figure
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