595 research outputs found
Implementation of quantum gates and preparation of entangled states in cavity QED with cold trapped ions
We propose a scheme to perform basic gates of quantum computing and prepare
entangled states in a system with cold trapped ions located in a single mode
optical cavity. General quantum computing can be made with both motional state
of the trapped ion and cavity state being qubits. We can also generate
different kinds of entangled states in such a system without state reduction,
and can transfer quantum states from the ion in one trap to the ion in another
trap. Experimental requirement for achieving our scheme is discussed.Comment: To appear in J. Opt.
Collective spin systems in dispersive optical cavity QED: Quantum phase transitions and entanglement
We propose a cavity QED setup which implements a dissipative
Lipkin-Meshkov-Glick model -- an interacting collective spin system. By varying
the external model parameters the system can be made to undergo both first-and
second-order quantum phase transitions, which are signified by dramatic changes
in cavity output field properties, such as the probe laser transmission
spectrum. The steady-state entanglement between pairs of atoms is shown to peak
at the critical points and can be experimentally determined by suitable
measurements on the cavity output field. The entanglement dynamics also
exhibits pronounced variations in the vicinities of the phase transitions.Comment: 19 pages, 18 figures, shortened versio
Efficient routing of single photons by one atom and a microtoroidal cavity
Single photons from a coherent input are efficiently redirected to a separate
output by way of a fiber-coupled microtoroidal cavity interacting with
individual Cesium atoms. By operating in an overcoupled regime for the
input-output to a tapered fiber, our system functions as a quantum router with
high efficiency for photon sorting. Single photons are reflected and excess
photons transmitted, as confirmed by observations of photon antibunching
(bunching) for the reflected (transmitted) light. Our photon router is robust
against large variations of atomic position and input power, with the observed
photon antibunching persisting for intracavity photon number 0.03 \lesssim n
\lesssim 0.7
Cooling to the Ground State of Axial Motion for One Atom Strongly Coupled to an Optical Cavity
Localization to the ground state of axial motion is demonstrated for a
single, trapped atom strongly coupled to the field of a high finesse optical
resonator. The axial atomic motion is cooled by way of coherent Raman
transitions on the red vibrational sideband. An efficient state detection
scheme enabled by strong coupling in cavity QED is used to record the Raman
spectrum, from which the state of atomic motion is inferred. We find that the
lowest vibrational level of the axial potential with zero-point energy 13uK is
occupied with probability P0~0.95.Comment: 5 pages, 4 figure
Multipartite Entanglement and Quantum State Exchange
We investigate multipartite entanglement in relation to the theoretical
process of quantum state exchange. In particular, we consider such entanglement
for a certain pure state involving two groups of N trapped atoms. The state,
which can be produced via quantum state exchange, is analogous to the
steady-state intracavity state of the subthreshold optical nondegenerate
parametric amplifier. We show that, first, it possesses some 2N-way
entanglement. Second, we place a lower bound on the amount of such entanglement
in the state using a novel measure called the entanglement of minimum bipartite
entropy.Comment: 12 pages, 4 figure
Field correlations and effective two level atom-cavity systems
We analyse the properties of the second order correlation functions of the
electromagnetic field in atom-cavity systems that approximate two-level
systems. It is shown that a recently-developed polariton formalism can be used
to account for all the properties of the correlations, if the analysis is
extended to include two manifolds - corresponding to the ground state and the
states excited by a single photon - rather than just two levels.Comment: 4 pages, 2 figures, published versio
Comment on ``Creating Metastable Schroedinger Cat States''
After a careful analysis of the feedback model recently proposed by Slosser
and Milburn [Phys. Rev. Lett. 75, 418 (1995)], we are led to the conclusion
that---under realistic conditions---their scheme is not significantly more
effective in the production of linear superpositions of macroscopically
distinguishable quantum states than the usual quantum-optical Kerr effect.Comment: 1 page, RevTeX, 1 eps figure (fig_1.eps), accepted for publication in
Physical Review Letters [Phys. Rev. Lett. 77 (9) (1996)
Motion-light parametric amplifier and entanglement distributor
We propose a scheme for entangling the motional mode of a trapped atom with a
propagating light field via a cavity-mediated parametric interaction. We then
show that if this light field is subsequently coupled to a second distant atom
via a cavity-mediated linear-mixing interaction, it is possible to transfer the
entanglement from the light beam to the motional mode of the second atom to
create an EPR-type entangled state of the positions and momenta of two
distantly-separated atoms.Comment: 9 pages, 8 figures, REVTe
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