525 research outputs found
Determination of the s-wave Scattering Length of Chromium
We have measured the deca-triplet s-wave scattering length of the bosonic
chromium isotopes Cr and Cr. From the time constants for
cross-dimensional thermalization in atomic samples we have determined the
magnitudes and ,
where . By measuring the rethermalization rate of Cr over a
wide temperature range and comparing the temperature dependence with the
effective-range theory and single-channel calculations, we have obtained strong
evidence that the sign of is positive. Rescaling our Cr
model potential to Cr strongly suggests that is positive,
too.Comment: v3: corrected typo in y-axis scaling of Figs. 3 and
Early Seizure Detection Based on Cardiac Autonomic Regulation Dynamics
Epilepsy is a neurological disorder that causes changes in the autonomic nervous system. Heart rate variability (HRV) reflects the regulation of cardiac activity and autonomic nervous system tone. The early detection of epileptic seizures could foster the use of new treatment approaches. This study presents a new methodology for the prediction of epileptic seizures using HRV signals. Eigendecomposition of HRV parameter covariance matrices was used to create an input for a support vector machine (SVM)-based classifier. We analyzed clinical data from 12 patients (9 female; 3 male; age 34.5 ± 7.5 years), involving 34 seizures and a total of 55.2 h of interictal electrocardiogram (ECG) recordings. Data from 123.6 h of ECG recordings from healthy subjects were used to test false positive rate per hour (FP/h) in a completely independent data set. Our methodological approach allowed the detection of impending seizures from 5 min to just before the onset of a clinical/electrical seizure with a sensitivity of 94.1%. The FP rate was 0.49 h−1 in the recordings from patients with epilepsy and 0.19 h−1 in the recordings from healthy subjects. Our results suggest that it is feasible to use the dynamics of HRV parameters for the early detection and, potentially, the prediction of epileptic seizures
Manipulation of Cold Atomic Collisions by Cavity QED Effects
We show how the dynamics of collisions between cold atoms can be manipulated
by a modification of spontaneous emission times. This is achieved by placing
the atomic sample in a resonant optical cavity. Spontaneous emission is
enhanced by a combination of multiparticle entanglement together with a higher
density of modes of the modified vacuum field, in a situation akin to
superradiance. A specific situation is considered and we show that this effect
can be experimentally observed as a large suppression in trap-loss rates.Comment: RevTex, 2 EPS figures; scheduled for Phys. Rev. Lett. 19 Feb 01, with
minor change
Formation of Pairing Fields in Resonantly Coupled Atomic and Molecular Bose-Einstein Condensates
In this paper, we show that pair-correlations may play an important role in
the quantum statistical properties of a Bose-Einstein condensed gas composed of
an atomic field resonantly coupled with a corresponding field of molecular
dimers. Specifically, pair-correlations in this system can dramatically modify
the coherent and incoherent transfer between the atomic and molecular fields.Comment: 4 pages, 4 figure
Stimulated Raman adiabatic passage from an atomic to a molecular Bose-Einstein condensate
The process of stimulated Raman adiabatic passage (STIRAP) provides a
possible route for the generation of a coherent molecular Bose-Einstein
condensate (BEC) from an atomic BEC. We analyze this process in a
three-dimensional mean-field theory, including atom-atom interactions and
non-resonant intermediate levels. We find that the process is feasible, but at
larger Rabi frequencies than anticipated from a crude single-mode lossless
analysis, due to two-photon dephasing caused by the atomic interactions. We
then identify optimal strategies in STIRAP allowing one to maintain high
conversion efficiencies with smaller Rabi frequencies and under experimentally
less demanding conditions.Comment: Final published versio
Formation of Two Component Bose Condensate During the Chemical Potential Curve Crossing
In this article we study the formation of the two modes Bose-Einstein
condensate and the correlation between them. We show that beyond the mean field
approximation the dissociation of a molecular condensate due to the chemical
potential curve crossing leads to the formation of two modes condensate. We
also show that these two modes are correlated in a two mode squeezed state.Comment: 10 page
Autler-Townes splitting in two-color photoassociation of 6Li
We report on high-resolution two-color photoassociation spectroscopy in the
triplet system of magneto-optically trapped 6Li. The absolute transition
frequencies have been measured. Strong optical coupling of the bound molecular
states has been observed as Autler-Townes splitting in the photoassociation
signal. The spontaneous bound-bound transition rate is determined and the
molecule formation rate is estimated. The observed lineshapes are in good
agreement with the theoretical model.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. A (Rapid
Communication
Theoretical model for ultracold molecule formation via adaptive feedback control
We investigate pump-dump photoassociation of ultracold molecules with
amplitude- and phase-modulated femtosecond laser pulses. For this purpose a
perturbative model for the light-matter interaction is developed and combined
with a genetic algorithm for adaptive feedback control of the laser pulse
shapes. The model is applied to the formation of 85Rb2 molecules in a
magneto-optical trap. We find for optimized pulse shapes an improvement for the
formation of ground state molecules by more than a factor of 10 compared to
unshaped pulses at the same pump-dump delay time, and by 40% compared to
unshaped pulses at the respective optimal pump-dump delay time. Since our model
yields directly the spectral amplitudes and phases of the optimized pulses, the
results are directly applicable in pulse shaping experiments
Quantum effects on the dynamics of a two-mode atom-molecule Bose-Einstein condensate
We study the system of coupled atomic and molecular condensates within the
two-mode model and beyond mean-field theory (MFT). Large amplitude
atom-molecule coherent oscillations are shown to be damped by the rapid growth
of fluctuations near the dynamically unstable molecular mode. This result
contradicts earlier predictions about the recovery of atom-molecule
oscillations in the two-mode limit. The frequency of the damped oscillation is
also shown to scale as with the total number of atoms ,
rather than the expected pure scaling. Using a linearized model, we
obtain analytical expressions for the initial depletion of the molecular
condensate in the vicinity of the instability, and show that the important
effect neglected by mean field theory is an initially non-exponential
`spontaneous' dissociation into the atomic vacuum. Starting with a small
population in the atomic mode, the initial dissociation rate is sensitive to
the exact atomic amplitudes, with the fastest (super-exponential) rate observed
for the entangled state, formed by spontaneous dissociation.Comment: LaTeX, 5 pages, 3 PostScript figures, uses REVTeX and epsfig,
submitted to Physical Review A, Rapid Communication
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