37 research outputs found
Feshbach Resonance Induced Fano Interference in Photoassociation
We consider photoassociation from a state of two free atoms when the
continuum state is close to a magnetic field induced Feshbach resonance and
analyze Fano interference in photoassociation. We show that the minimum in
photoassociation profiles characterized by the Fano asymmetry parameter is
independent of laser intensity, while the maximum explicitly depends on laser
intensity. We further discuss the possibility of nonlinear Fano effect in
photoassociation near a Feshbach resonance.Comment: 6 pages 4 figures, substantial change with new results in version
Finite temperature effects in light scattering off Cooper-paired Fermi atoms
We study stimulated light scattering off a superfluid Fermi gas of atoms at
finite temperature. We derive response function that takes into account vertex
correction due to final state interactions; and analyze finite temperature
effects on collective and quasiparticle excitations of a uniform superfluid
Fermi gas. Light polarization is shown to play an important role in
excitations. Our results suggest that it is possible to excite
Bogoliubov-Anderson phonon at a large scattering length by light scattering.Comment: 18 pages, 4 figures, Accepted in J. Phys. B: At. Mol. & Opt. Phy
Magneto-optical Feshbach resonance: Controlling cold collision with quantum interference
We propose a method of controlling two-atom interaction using both magnetic
and laser fields. We analyse the role of quantum interference between magnetic
and optical Feshbach resonances in controlling cold collision. In particular,
we demonstrate that this method allows us to suppress inelastic and enhance
elastic scattering cross sections. Quantum interference is shown to modify
significantly the threshold behaviour and resonant interaction of ultracold
atoms. Furthermore, we show that it is possible to manipulate not only the
spherically symmetric s-wave interaction but also the anisotropic higher
partial-wave interactions which are particularly important for high temperature
superfluid or superconducting phases of matter.Comment: 7 pages 3 figures, some minor errors are corrected, Accepted in J.
Phys.
Resonant enhancement of ultracold photoassociation rate by electric field induced anisotropic interaction
We study the effects of a static electric field on the photoassociation of a
heteronuclear atom-pair into a polar molecule. The interaction of permanent
dipole moment with a static electric field largely affects the ground state
continuum wave function of the atom-pair at short separations where
photoassociation transitions occur according to Franck-Condon principle.
Electric field induced anisotropic interaction between two heteronuclear ground
state atoms leads to scattering resonances at some specific electric fields.
Near such resonances the amplitude of scattering wave function at short
separation increases by several orders of magnitude. As a result,
photoaasociation rate is enhanced by several orders of magnitude near the
resonances. We discuss in detail electric field modified atom-atom scattering
properties and resonances. We calculate photoassociation rate that shows giant
enhancement due to electric field tunable anisotropic resonances. We present
selected results among which particularly important are the excitations of
higher rotational levels in ultracold photoassociation due to electric field
tunable resonances.Comment: 14 pages,9 figure
Utility of Ottawa ankle rules in excluding ankle fractures in Indian scenario
Background: Patients with acute ankle injuries form a major bulk in outdoor and emergency room, and many of them get radiographs done to rule out fractures. Ottawa ankle rules (OAR) may reduce the need for unnecessary radiographs by detecting fractures only with help of simple clinical findings. We conducted this study to see the extent of usefulness of these rules in our day-to-day practice.Methods: Our study is observational in nature. A total of 107 patients who visited the clinic of the chief investigator between the time period from 1st January 2019 to 31st December 2020, fulfilling inclusion criteria and willing to participate, were enrolled. The patients were examined clinically, and the assessor recorded the findings on a previously prepared assessment form. Data analysis was done from the master chart.Results: Among the 107 patients, 46 patients were ‘suspicion positive’ by OAR. After the radiographic assessment, we found 11 fractures, all of which belonged to the ‘suspicion positive’ group. Statistical analysis showed that OAR had a sensitivity of 100% for ankle fractures, whereas specificity for the same was 63.54%. We found the positive predictive value to be 23.91% and negative predictive value to be 100%, positive likelihood ratio of 2.74, and negative likelihood ratio of 0.Conclusions: OAR is an easy and reliable tool to screen ankle fractures. In a country with as massive a health care burden as ours, it can reduce the number of unnecessary radiographs and thus reduce exposure, cost, and time of medical professionals
Suppression of power-broadening in strong-coupling photoassociation in the presence of a Feshbach resonance
Photoassociation (PA) spectrum in the presence of a magnetic Feshbach
resonance is analyzed. Nonperturbative solution of the problem yields
analytical expressions for PA linewidth and shift which are applicable for
arbitrary PA laser intensity and magnetic field tuning of Feshbach Resonance.
We show that by tuning magnetic field close to Fano minimum, it is possible to
suppress power broadening at increased laser intensities. This occurs due to
quantum interference of PA transitions from unperturbed and perturbed
continuum. Line narrowing at high laser intensities is accompanied by large
spectral shifts. We briefly discuss important consequences of line narrowing in
cold collisions.Comment: 12 pages, 5 figure
Quantum theory of dissipation of a harmonic oscillator coupled to a nonequilibrium bath; Wigner-Weisskopf decay and physical spectra
We extend the quantum theory of dissipation in the context of
system-reservoir model, where the reservoir in question is kept in a
nonequilibrium condition. Based on a systematic separation of time scales
involved in the dynamics, appropriate generalizations of the
fluctuation-dissipation and Einstein's relations have been pointed out. We show
that the Wigner-Weisskopf decay of the system mode results in a rate constant
which depending on the relaxation of nonequilibrium bath is dynamically
modified. We also calculate the time-dependent spectra of a cavity mode with a
suitable gain when the cavity is kept in contact with a nonequilibrium bath.Comment: Plain Latex, 28 pages, 2 PS figure
Light scattering in Cooper-paired Fermi atoms
We present a detailed theoretical study of light scattering off superfluid
trapped Fermi gas of atoms at zero temperature. We apply Nambu-Gorkov formalism
of superconductivity to calculate the response function of superfluid gas due
to stimulated light scattering taking into account the final state
interactions. The polarization of light has been shown to play a significant
role in response of Cooper-pairs in the presence of a magnetic field.
Particularly important is a scheme of polarization-selective light scattering
by either spin-component of the Cooper-pairs leading to the single-particle
excitations of one spin-component only. These excitations have a threshold of
where is the superfluid gap energy. Furthermore,
polarization-selective light scattering allows for unequal energy and momentum
transfer to the two partner atoms of a Cooper-pair. In the regime of low energy
() and low momentum (, being the Fermi
velocity) transfer, a small difference in momentum transfers to the two
spin-components may be useful in exciting Bogoliubov-Anderson phonon mode. We
present detailed results on the dynamic structure factor (DSF) deduced from the
response function making use of generalized fluctuation-dissipation theorem.
Model calculations using local density approximation for trapped superfluid
Fermi gas shows that when the energy transfer is less than , where
refers to the gap at the trap center, DSF as a function of energy
transfer has reduced gradient compared to that of normal Fermi gas.Comment: single column, 26 pages, 10 figures; Title changed, discussion on
experimental implication added in concluding section. Accepted for
publication in J. Phys.