326 research outputs found
Antiferromagnetic phase transition in a nonequilibrium lattice of Rydberg atoms
We study a driven-dissipative system of atoms in the presence of laser
excitation to a Rydberg state and spontaneous emission. The atoms interact via
the blockade effect, whereby an atom in the Rydberg state shifts the Rydberg
level of neighboring atoms. We use mean-field theory to study how the Rydberg
population varies in space. As the laser frequency changes, there is a
continuous transition between the uniform and antiferromagnetic phases. The
nonequilibrium nature also leads to a novel oscillatory phase and bistability
between the uniform and antiferromagnetic phases.Comment: 4 pages + appendi
Collective quantum jumps of Rydberg atoms
We study an open quantum system of atoms with long-range Rydberg interaction,
laser driving, and spontaneous emission. Over time, the system occasionally
jumps between a state of low Rydberg population and a state of high Rydberg
population. The jumps are inherently collective and in fact exist only for a
large number of atoms. We explain how entanglement and quantum measurement
enable the jumps, which are otherwise classically forbidden.Comment: 4 page
Generalized spin squeezing inequalities in qubit systems: theory and experiment
We present detailed derivations, various improvements and application to
concrete experimental data of spin squeezing inequalities formulated recently
by some of us [Phys. Rev. Lett. {\bf 95}, 120502 (2005)]. These inequalities
generalize the concept of the spin squeezing parameter, and provide necessary
and sufficient conditions for genuine 2-, or 3- qubit entanglement for
symmetric states, and sufficient entanglement condition for general -qubit
states. We apply our method to theoretical study of Dicke states, and, in
particular, to -states of qubits. Then, we analyze the recently
experimentally generated 7- and 8-ion -states [Nature {\bf 438}, 643
(2005)]. We also present some novel details concerning this experiment.
Finally, we improve criteria for detection of genuine tripartite entanglement
based on entanglement witnesses.Comment: Final versio
Coupling two laser-cooled ions via a room-temperature conductor
We demonstrate coupling between the motions of two independently trapped ions
with a separation distance of 620 m. The ion-ion interaction is enhanced
via a room-temperature electrically floating metallic wire which connects two
surface traps. Tuning the motion of both ions into resonance, we show flow of
energy with a coupling rate of 11 Hz. Quantum-coherent coupling is hindered by
strong surface electric-field noise in our device. Our ion wire-ion system
demonstrates that room-temperature conductors can be used to mediate and tune
interactions between independently trapped charges over distances beyond those
achievable with free-space dipole-dipole coupling. This technology may be used
to sympathetically cool or entangle remotely trapped charges and enable
coupling between disparate physical systems
Integrated Atom Detector Based on Field Ionization near Carbon Nanotubes
We demonstrate an atom detector based on field ionization and subsequent ion
counting. We make use of field enhancement near tips of carbon nanotubes to
reach extreme electrostatic field values of up to 9x10^9 V/m, which ionize
ground state rubidium atoms. The detector is based on a carpet of multiwall
carbon nanotubes grown on a substrate and used for field ionization, and a
channel electron multiplier used for ion counting. We measure the field
enhancement at the tips of carbon nanotubes by field emission of electrons. We
demonstrate the operation of the field ionization detector by counting atoms
from a thermal beam of a rubidium dispenser source. By measuring the ionization
rate of rubidium as a function of the applied detector voltage we identify the
field ionization distance, which is below a few tens of nanometers in front of
nanotube tips. We deduce from the experimental data that field ionization of
rubidium near nanotube tips takes place on a time scale faster than 10^(-10)s.
This property is particularly interesting for the development of fast atom
detectors suitable for measuring correlations in ultracold quantum gases. We
also describe an application of the detector as partial pressure gauge.Comment: 7 pages, 8 figure
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