987 research outputs found
Generation of Superposition Spin States in an Atomic Ensemble
A method for generating a mesoscopic superposition state of the collective
spin variable of a gas of atoms is proposed. The state consists of a
superposition of the atomic spins pointing in two slightly different
directions. It is obtained by using off resonant light to carry out Quantum Non
Demolition Measurements of the spins. The relevant experimental conditions,
which require very dense atomic samples, can be realized with presently
available techniques. Long-lived atomic superposition states may become useful
as an off-line resource for quantum computing with otherwise linear operations.Comment: 5 pages, 2 figures, accepted in Phys. Rev. Let
Characterization of high finesse mirrors: loss, phase shifts and mode structure in an optical cavity
An extensive characterization of high finesse optical cavities used in cavity
QED experiments is described. Different techniques in the measurement of the
loss and phase shifts associated with the mirror coatings are discussed and
their agreement shown. Issues of cavity field mode structure supported by the
dielectric coatings are related to our effort to achieve the strongest possible
coupling between an atom and the cavity.Comment: 8 pages, 4 figure
Quasi-spin wave quantum memories with dynamic symmetry
For the two-mode exciton system formed by the quasi-spin wave collective
excitation of many atoms fixed at the lattice sites of a crystal, we
discover a dynamic symmetry depicted by the semi-direct product algebra
in the large limit with low excitations. With the
help of the spectral generating algebra method, we obtain a larger class of
exact zero-eigenvalue states adiabatically interpolating between the initial
state of photon-type and the final state of quasi-spin wave exciton-type. The
conditions for the adiabatic passage of dark states are shown to be valid, even
with the presence of the level degeneracy. These theoretical results can lead
to propose new protocol of implementing quantum memory robust against quantum
decoherence.Comment: 6 pages, 2 figures,with some reservations. Accepted for publication
in Phys. Rev .Let
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
Simulations of atomic trajectories near a dielectric surface
We present a semiclassical model of an atom moving in the evanescent field of
a microtoroidal resonator. Atoms falling through whispering-gallery modes can
achieve strong, coherent coupling with the cavity at distances of approximately
100 nanometers from the surface; in this regime, surface-induced Casmir-Polder
level shifts become significant for atomic motion and detection. Atomic transit
events detected in recent experiments are analyzed with our simulation, which
is extended to consider atom trapping in the evanescent field of a microtoroid.Comment: 29 pages, 10 figure
Conditional large Fock state preparation and field state reconstruction in Cavity QED
We propose a scheme for producing large Fock states in Cavity QED via the
implementation of a highly selective atom-field interaction. It is based on
Raman excitation of a three-level atom by a classical field and a quantized
field mode. Selectivity appears when one tunes to resonance a specific
transition inside a chosen atom-field subspace, while other transitions remain
dispersive, as a consequence of the field dependent electronic energy shifts.
We show that this scheme can be also employed for reconstructing, in a new and
efficient way, the Wigner function of the cavity field state.Comment: 4 Revtex pages with 3 postscript figures. Submitted for publicatio
Are Coronal Loops Isothermal or Multithermal? Yes!
Surprisingly few solar coronal loops have been observed simultaneously with
TRACE and SOHO/CDS, and even fewer analyses of these loops have been conducted
and published. The SOHO Joint Observing Program 146 was designed in part to
provide the simultaneous observations required for in-depth temperature
analysis of active region loops and determine whether these loops are
isothermal or multithermal. The data analyzed in this paper were taken on 2003
January 17 of AR 10250. We used TRACE filter ratios, emission measure loci, and
two methods of differential emission measure analysis to examine the
temperature structure of three different loops. TRACE and CDS observations
agree that Loop 1 is isothermal with Log T 5.85, both along the line of
sight as well as along the length of the loop leg that is visible in the CDS
field of view. Loop 2 is hotter than Loop 1. It is multithermal along the line
of sight, with significant emission between 6.2 Log T 6.4, but the loop
apex region is out of the CDS field of view so it is not possible to determine
the temperature distribution as a function of loop height. Loop 3 also appears
to be multithermal, but a blended loop that is just barely resolved with CDS
may be adding cool emission to the Loop 3 intensities and complicating our
results. So, are coronal loops isothermal or multithermal? The answer appears
to be yes
Evolving geometric phase and its dynamical manifestation as a frequency shift: An optical experiment
We show that an evolving geometric phase induces a frequency shift. We report an optical experiment where we employ this effect to offset the frequency of a laser beam
Simon et al. Reply
In our letter [1] the electric fields of both the incident beam and the beam reflected from the mirror m1 are described in the same transverse coordinate system (x,y), by the pair of complex electric field components Ex,Ey arranged as a column. ... Bhandari's difficulty [2] originates partly from a possible lack of clarity in the specification of the polarization states in our Letter and partly from a misconception that the return beam going through L will necessarily imply retracing of the circuit yielding a net zero geometric phase
On the suppression of the diffusion and the quantum nature of a cavity mode. Optical bistability; forces and friction in driven cavities
A new analytical method is presented here, offering a physical view of driven
cavities where the external field cannot be neglected. We introduce a new
dimensionless complex parameter, intrinsically linked to the cooperativity
parameter of optical bistability, and analogous to the scaled Rabbi frequency
for driven systems where the field is classical. Classes of steady states are
iteratively constructed and expressions for the diffusion and friction
coefficients at lowest order also derived. They have in most cases the same
mathematical form as their free-space analog. The method offers a semiclassical
explanation for two recent experiments of one atom trapping in a high Q cavity
where the excited state is significantly saturated. Our results refute both
claims of atom trapping by a quantized cavity mode, single or not. Finally, it
is argued that the parameter newly constructed, as well as the groundwork of
this method, are at least companions of the cooperativity parameter and its
mother theory. In particular, we lay the stress on the apparently more
fundamental role of our structure parameter.Comment: 24 pages, 7 figures. Submitted to J. Phys. B: At. Mol. Opt. Phy
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