5,264 research outputs found
Photon sorters and QND detectors using single photon emitters
We discuss a new method for realizing number-resolving and non-demolition
photo detectors by strong coupling of light to individual single photon
emitters, which act as strong optical non-linearities. As a specific
application we show how these elements can be integrated into an error-proof
Bell state analyzer, whose efficiency exceeds the best possible performance
with linear optics even for a modest atom-field coupling. The methods are
error-proof in the sense that every detection event unambiguously projects the
photon state onto a Fock or Bell state.Comment: revised and enlarged version, 6+ pages, 5 figure
Characterization of topological states on a lattice with Chern number
We study Chern numbers to characterize the ground state of strongly
interacting systems on a lattice. This method allows us to perform a numerical
characterization of bosonic fractional quantum Hall (FQH) states on a lattice
where conventional overlap calculation with known continuum case such as
Laughlin state, breaks down due to the lattice structure or dipole-dipole
interaction. The non-vanishing Chern number indicates the existence of a
topological order in the degenerate ground state manifold.Comment: 5 pages, 3 figures, V2: changes in the presentatio
Bogoliubov theory of entanglement in a Bose-Einstein condensate
We consider a Bose-Einstein condensate which is illuminated by a short
resonant light pulse that coherently couples two internal states of the atoms.
We show that the subsequent time evolution prepares the atoms in an interesting
entangled state called a spin squeezed state. This evolution is analysed in
detail by developing a Bogoliubov theory which describes the entanglement of
the atoms. Our calculation is a consistent expansion in , where
is the number of particles in the condensate, and our theory predict that it is
possible to produce spin squeezing by at least a factor of . Within
the Bogoliubov approximation this result is independent of temperature.Comment: 14 pages, including 5 figures, minor changes in the presentatio
Opto-mechanical transducers for long-distance quantum communication
We describe a new scheme to interconvert stationary and photonic qubits which
is based on indirect qubit-light interactions mediated by a mechanical
resonator. This approach does not rely on the specific optical response of the
qubit and thereby enables optical quantum interfaces for a wide range of solid
state spin and charge based systems. We discuss the implementation of quantum
state transfer protocols between distant nodes of a large scale network and
evaluate the effect of the main noise sources on the resulting state transfer
fidelities. For the specific examples of electronic spin qubits and
superconducting charge qubits we show that high fidelity quantum communication
protocols can be implemented under realistic experimental conditions.Comment: Version as accepted by PR
Multi-particle entanglement of hot trapped ions
We propose an efficient method to produce multi-particle entangled states of
ions in an ion trap for which a wide range of interesting effects and
applications have been suggested. Our preparation scheme exploits the
collective vibrational motion of the ions, but it works in such a way that this
motion need not be fully controlled in the experiment. The ions may, e.g., be
in thermal motion and exchange mechanical energy with a surrounding heat bath
without detrimental effects on the internal state preparation. Our scheme does
not require access to the individual ions in the trap.Comment: 4 pages, including 3 figures. To appear in Phys. Rev. Lett. This
paper previously appeared under the name "Schrodingers cat in a hot trap".
The paper has been revised according to Phys. Rev. policy on Schrodinger
cats. No cats were harmed during the production of this manuscrip
Stability of atomic clocks based on entangled atoms
We analyze the effect of realistic noise sources for an atomic clock
consisting of a local oscillator that is actively locked to a spin-squeezed
(entangled) ensemble of atoms. We show that the use of entangled states can
lead to an improvement of the long-term stability of the clock when the
measurement is limited by decoherence associated with instability of the local
oscillator combined with fluctuations in the atomic ensemble's Bloch vector.
Atomic states with a moderate degree of entanglement yield the maximal clock
stability, resulting in an improvement that scales as compared to the
atomic shot noise level.Comment: 4 pages, 2 figures, revtex
Structure of boson systems beyond the mean-field
We investigate systems of identical bosons with the focus on two-body
correlations. We use the hyperspherical adiabatic method and a decomposition of
the wave function in two-body amplitudes. An analytic parametrization is used
for the adiabatic effective radial potential. We discuss the structure of a
condensate for arbitrary scattering length. Stability and time scales for
various decay processes are estimated. The previously predicted Efimov-like
states are found to be very narrow. We discuss the validity conditions and
formal connections between the zero- and finite-range mean-field
approximations, Faddeev-Yakubovskii formulation, Jastrow ansatz, and the
present method. We compare numerical results from present work with mean-field
calculations and discuss qualitatively the connection with measurements.Comment: 26 pages, 6 figures, submitted to J. Phys. B. Ver. 2 is 28 pages with
modified figures and discussion
Spin Squeezing in the Ising Model
We analyze the collective spin noise in interacting spin systems. General
expressions are derived for the short time behaviour of spin systems with
general spin-spin interactions, and we suggest optimum experimental conditions
for the detection of spin squeezing. For Ising models with site dependent
nearest neighbour interactions general expressions are presented for the spin
squeezing parameter for all times. The reduction of collective spin noise can
be used to verify the entangling powers of quantum computer architectures based
on interacting spins.Comment: 7 pages, including 3 figure
Entanglement and Extreme Spin Squeezing
For any mean value of a cartesian component of a spin vector we identify the
smallest possible uncertainty in any of the orthogonal components. The
corresponding states are optimal for spectroscopy and atomic clocks. We show
that the results for different spin J can be used to identify entanglement and
to quantity the depth of entanglement in systems with many particles. With the
procedure developed in this letter, collective spin measurements on an ensemble
of particles can be used as an experimental proof of multi-particle
entanglementComment: 4 pages, 2 figures, minor changes in the presentatio
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