70 research outputs found
Efficient multiparticle entanglement via asymmetric Rydberg blockade
We present an efficient method for producing particle entangled states
using Rydberg blockade interactions. Optical excitation of Rydberg states that
interact weakly, yet have a strong coupling to a second control state is used
to achieve state dependent qubit rotations in small ensembles. On the basis of
quantitative calculations we predict that an N=8 Schr\"odinger cat state can be
produced with a fidelity of 84% in cold Rb atoms.Comment: 3 figure
Feshbach Molecules in a One-dimensional Optical Lattice
We present the theory of a pair of atoms in a one-dimensional optical lattice
interacting via a narrow Feshbach resonance. Using a two-channel description of
the resonance, we derive analytic results for the scattering states inside the
continuum band and the discrete bound states outside the band. We identify a
Fano resonance profile, and the survival probability of a molecule when swept
through the Bloch band of scattering states by varying an applied magnetic
field. We discuss how these results may be used to investigate the importance
of the structured nature of the continuum in experiments.Comment: 4 pages, 3 figure
Two-channel Feshbach physics in a structured continuum
We analyze the scattering and bound state physics of a pair of atoms in a
one-dimensional optical lattice interacting via a narrow Feshbach resonance.
The lattice provides a structured continuum allowing for the existence of bound
dimer states both below and above the continuum bands, with pairs above the
continuum stabilized by either repulsive interactions or their center of mass
motion. Inside the band the Feshbach coupling to a closed channel bound state
leads to a Fano resonance profile for the transmission, which may be mapped out
by RF- or photodissociative spectroscopy. We generalize the scattering length
concept to the one-dimensional lattice, where a scattering length may be
defined at both the lower and the upper continuum thresholds. As a function of
the applied magnetic field the scattering length at either band edge exhibits
the usual Feshbach divergence when a bound state enters or exits the continuum.
Near the scattering length divergences the binding energy and wavefunction of
the weakly bound dimer state acquires a universal form reminiscent of those of
free-space Feshbach molecules. We give numerical examples of our analytic
results for a specific Feshbach resonance, which has been studied
experimentally.Comment: 18 pages, 9 embedded figure
Scattering and binding of different atomic species in a one-dimensional optical lattice
The theory of scattering of atom pairs in a periodic potential is presented
for the case of different atoms. When the scattering dynamics is restricted to
the lowest Bloch band of the periodic potential, a separation in relative and
average discrete coordinates applies and makes the problem analytically
tractable, and we present a number of new results and features compared to the
case of identical atoms.Comment: 5 pages, 4 figure
Universal Quantum Computation in a Neutral Atom Decoherence Free Subspace
In this paper, we propose a way to achieve protected universal computation in
a neutral atom quantum computer subject to collective dephasing. Our proposal
relies on the existence of a Decoherence Free Subspace (DFS), resulting from
symmetry properties of the errors. After briefly describing the physical system
and the error model considered, we show how to encode information into the DFS
and build a complete set of safe universal gates. Finally, we provide numerical
simulations for the fidelity of the different gates in the presence of
time-dependent phase errors and discuss their performance and practical
feasibility.Comment: 7 pages, 8 figure
Quantum information with Rydberg atoms
Rydberg atoms with principal quantum number n >> 1 have exaggerated atomic
properties including dipole-dipole interactions that scale as n^4 and radiative
lifetimes that scale as n^3. It was proposed a decade ago to take advantage of
these properties to implement quantum gates between neutral atom qubits. The
availability of a strong, long-range interaction that can be coherently turned
on and off is an enabling resource for a wide range of quantum information
tasks stretching far beyond the original gate proposal. Rydberg enabled
capabilities include long-range two-qubit gates, collective encoding of
multi-qubit registers, implementation of robust light-atom quantum interfaces,
and the potential for simulating quantum many body physics. We review the
advances of the last decade, covering both theoretical and experimental aspects
of Rydberg mediated quantum information processing.Comment: accepted version, to appear in Rev. Mod. Phys., 40 figures
Bright solitons and soliton trains in a fermion-fermion mixture
We use a time-dependent dynamical mean-field-hydrodynamic model to predict
and study bright solitons in a degenerate fermion-fermion mixture in a
quasi-one-dimensional cigar-shaped geometry using variational and numerical
methods. Due to a strong Pauli-blocking repulsion among identical
spin-polarized fermions at short distances there cannot be bright solitons for
repulsive interspecies fermion-fermion interactions. However, stable bright
solitons can be formed for a sufficiently attractive interspecies interaction.
We perform a numerical stability analysis of these solitons and also
demonstrate the formation of soliton trains. These fermionic solitons can be
formed and studied in laboratory with present technology.Comment: 5 pages, 7 figure
Unraveling quantum dissipation in the frequency domain
We present a quantum Monte Carlo method for solving the evolution of an open
quantum system. In our approach, the density operator evolution is unraveled in
the frequency domain. Significant advantages of this approach arise when the
frequency of each dissipative event conveys information about the state of the
system.Comment: 4 pages, 4 Postscript figures, uses RevTe
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