1,376 research outputs found
Dynamical Crystallization in the Dipole Blockade of Ultracold Atoms
We describe a method for controlling many-body states in extended ensembles
of Rydberg atoms, forming crystalline structures during laser excitation of a
frozen atomic gas. Specifically, we predict the existence of an excitation
number staircase in laser excitation of atomic ensembles into Rydberg states.
Each step corresponds to a crystalline state with a well-defined of regularly
spaced Rydberg atoms. We show that such states can be selectively excited by
chirped laser pulses. Finally, we demonstarte that, sing quantum state transfer
from atoms to light, such crystals can be used to create crystalline photonic
states and can be probed via photon correlation measurements
Photonic quantum transport in a nonlinear optical fiber
We theoretically study the transmission of few-photon quantum fields through a strongly nonlinear optical medium. We develop a general approach to investigate nonequilibrium quantum transport of bosonic fields through a finite-size nonlinear medium and apply it to a recently demonstrated experimental system where cold atoms are loaded in a hollow-core optical fiber. We show that when the interaction between photons is effectively repulsive, the system acts as a single-photon switch. In the case of attractive interaction, the system can exhibit either antibunching or bunching, associated with the resonant excitation of bound states of photons by the input field. These effects can be observed by probing statistics of photons transmitted through the nonlinear fiber
Quantum storage via refractive index control
Off-resonant Raman interaction of a single-photon wave packet and a classical
control field in an atomic medium with controlled refractive index is
investigated. It is shown that a continuous change of refractive index during
the interaction leads to the mapping of a single photon state to a
superposition of atomic collective excitations (spin waves) with different wave
vectors and visa versa. The suitability of refractive index control for
developing multichannel quantum memories is discussed and possible schemes of
implementation are considered.Comment: 6 pages, 2 figure
A fast and robust approach to long-distance quantum communication with atomic ensembles
Quantum repeaters create long-distance entanglement between quantum systems
while overcoming difficulties such as the attenuation of single photons in a
fiber. Recently, an implementation of a repeater protocol based on single
qubits in atomic ensembles and linear optics has been proposed [Nature 414, 413
(2001)]. Motivated by rapid experimental progress towards implementing that
protocol, here we develop a more efficient scheme compatible with active
purification of arbitrary errors. Using similar resources as the earlier
protocol, our approach intrinsically purifies leakage out of the logical
subspace and all errors within the logical subspace, leading to greatly
improved performance in the presence of experimental inefficiencies. Our
analysis indicates that our scheme could generate approximately one pair per 3
minutes over 1280 km distance with fidelity (F>78%) sufficient to violate
Bell's inequality.Comment: 10 pages, 4 figures, 5 tables (Two appendixes are added to justify
two claims used in the maintext.
Decay of super-currents in condensates in optical lattices
In this paper we discuss decay of superfluid currents in boson lattice
systems due to quantum tunneling and thermal activation mechanisms. We derive
asymptotic expressions for the decay rate near the critical current in two
regimes, deep in the superfluid phase and close to the superfluid-Mott
insulator transition. The broadening of the transition at the critical current
due to these decay mechanisms is more pronounced at lower dimensions. We also
find that the crossover temperature below which quantum decay dominates is
experimentally accessible in most cases. Finally, we discuss the dynamics of
the current decay and point out the difference between low and high currents.Comment: Contribution to the special issue of Journal of Superconductivity in
honor of Michael Tinkham's 75th birthda
Storage of light in atomic vapor
We report an experiment in which a light pulse is decelerated and trapped in
a vapor of Rb atoms, stored for a controlled period of time, and then released
on demand. We accomplish this storage of light by dynamically reducing the
group velocity of the light pulse to zero, so that the coherent excitation of
the light is reversibly mapped into a collective Zeeman (spin) coherence of the
Rb vapor
Efficient photon counting and single-photon generation using resonant nonlinear optics
The behavior of an atomic double lambda system in the presence of a strong
off-resonant classical field and a few-photon resonant quantum field is
examined. It is shown that the system possesses properties that allow a
single-photon state to be distilled from a multi-photon input wave packet. In
addition, the system is also capable of functioning as an efficient
photodetector discriminating between one- and two-photon wave packets with
arbitrarily high efficiency.Comment: 4 pages, 2 figure
Enhancing capacity of coherent optical information storage and transfer in a Bose-Einstein condensate
Coherent optical information storage capacity of an atomic Bose-Einstein
condensate is examined. Theory of slow light propagation in atomic clouds is
generalized to short pulse regime by taking into account group velocity
dispersion. It is shown that the number of stored pulses in the condensate can
be optimized for a particular coupling laser power, temperature and interatomic
interaction strength. Analytical results are derived for semi-ideal model of
the condensate using effective uniform density zone approximation. Detailed
numerical simulations are also performed. It is found that axial density
profile of the condensate protects the pulse against the group velocity
dispersion. Furthermore, taking into account finite radial size of the
condensate, multi-mode light propagation in atomic Bose-Einstein condensate is
investigated. The number of modes that can be supported by a condensate is
found. Single mode condition is determined as a function of experimentally
accessible parameters including trap size, temperature, condensate number
density and scattering length. Quantum coherent atom-light interaction schemes
are proposed for enhancing multi-mode light propagation effects.Comment: 12pages. Laser Physics, in pres
Superfluid-insulator transition in a moving system of interacting bosons
We analyze stability of superfluid currents in a system of strongly
interacting ultra-cold atoms in an optical lattice. We show that such a system
undergoes a dynamic, irreversible phase transition at a critical phase gradient
that depends on the interaction strength between atoms. At commensurate
filling, the phase boundary continuously interpolates between the classical
modulation instability of a weakly interacting condensate and the equilibrium
quantum phase transition into a Mott insulator state at which the critical
current vanishes. We argue that quantum fluctuations smear the transition
boundary in low dimensional systems. Finally we discuss the implications to
realistic experiments.Comment: updated refernces and introduction, minor correction
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