8,261 research outputs found
Entangled-state cycles from conditional quantum evolution
A system of cascaded qubits interacting via the oneway exchange of photons is
studied. While for general operating conditions the system evolves to a
superposition of Bell states (a dark state) in the long-time limit, under a
particular resonance condition no steady state is reached within a finite time.
We analyze the conditional quantum evolution (quantum trajectories) to
characterize the asymptotic behavior under this resonance condition. A distinct
bimodality is observed: for perfect qubit coupling, the system either evolves
to a maximally entangled Bell state without emitting photons (the dark state),
or executes a sustained entangled-state cycle - random switching between a pair
of Bell states while emitting a continuous photon stream; for imperfect
coupling, two entangled-state cycles coexist, between which a random selection
is made from one quantum trajectory to another.Comment: 12 pages, 10 figure
Quantum Teleportation of Light
Requirements for the successful teleportation of a beam of light, including
its temporal correlations, are discussed. Explicit expressions for the degrees
of first- and second-order optical coherence are derived. Teleportation of an
antibunched photon stream illustrates our results.Comment: 4 pages, 5 figure
From quantum feedback to probabilistic error correction: Manipulation of quantum beats in cavity QED
It is shown how to implement quantum feedback and probabilistic error
correction in an open quantum system consisting of a single atom, with ground-
and excited-state Zeeman structure, in a driven two-mode optical cavity. The
ground state superposition is manipulated and controlled through conditional
measurements and external fields, which shield the coherence and correct
quantum errors. Modeling of an experimentally realistic situation demonstrates
the robustness of the proposal for realization in the laboratory
Multipartite W states for chains of atoms conveyed through an optical cavity
We propose and work out a scheme to generate the entangled W states for a
chain of N four-level atoms which are transported through an optical cavity by
means of an optical lattice. This scheme is based on the combined laser-cavity
mediated interaction between distant and equally separated atoms and works in a
completely deterministic way for qubits encoded by two hyperfine levels of the
atoms. Only two parameters, namely the distance between the atoms and the
velocity of the chain, determine the effective interaction among the atoms and,
therefore, the degree of entanglement that is obtained for the overall chain of
N qubits. In particular, we work out the parameter regions for which the W
states are generated most reliably for chains of N = 2,3,4 and 5 atoms. In
addition, we analyze the sensitivity in the formation of entanglement for such
chains of qubits due to uncertainties produced by the oscillations of atoms in
optical lattices.Comment: 12 pages, revised version accepted in PR
"Modes of the universe" study of two-photon deterministic, passive quantum logical gates
We use the "modes of the universe" approach to study a cavity-mediated
two-photon logical gate recently proposed by Koshino, Ishizaka and Nakamura. We
clarify the relationship between the more commonly used input-output formalism,
and that of Koshino et al., and show that some elements of this gate had been
anticipated by other authors. We conclude that their proposed gate can work
both in the good and bad cavity limits, provided only that the pulses are long
enough. Our formalism allows us to estimate analytically the size of the
various error terms, and to follow the spectral evolution of the field + cavity
system in the course of the interaction.Comment: 9 pages, 8 figure
Development of a machine protection system for the Superconducting Beam Test Facility at Fermilab
Fermilab's Superconducting RF Beam Test Facility currently under construction
will produce electron beams capable of damaging the acceleration structures and
the beam line vacuum chambers in the event of an aberrant accelerator pulse.
The accelerator is being designed with the capability to operate with up to
3000 bunches per macro-pulse, 5Hz repetition rate and 1.5 GeV beam energy. It
will be able to sustain an average beam power of 72 KW at the bunch charge of
3.2 nC. Operation at full intensity will deposit enough energy in niobium
material to approach the melting point of 2500 {\deg}C. In the early phase with
only 3 cryomodules installed the facility will be capable of generating
electron beam energies of 810 MeV and an average beam power that approaches 40
KW. In either case a robust Machine Protection System (MPS) is required to
mitigate effects due to such large damage potentials. This paper will describe
the MPS system being developed, the system requirements and the controls issues
under consideration.Comment: 3 pp. 13th International Conference on Accelerator and Large
Experimental Physics Control Systems (ICALEPCS 2011). 10-14 Oct 2011.
Grenoble, Franc
Developmental Programming: Granulosa cell mRNA expression of differentiation, growth and apoptosis genes in abnormally large progestagenic follicles from androgenized ewes
High-fidelity atomic-state teleportation protocol with non-maximally-entangled states
We propose a protocol of the long-distance atomic state teleportation via
cavity decay, which allows for high-fidelity teleportation even with currently
available optical cavities. The protocol is based on the scheme proposed by
Bose \emph{et al.} [Phys. Rev. Lett. {\textbf{83}}, 5158 (1999)] but with one
important modification: it employs non-maximally-entangled states instead of
maximally entangled states.Comment: 8 pages, 6 figures, accepted for publication in Phys. Rev.
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