15 research outputs found
A Molecular Matter-Wave Amplifier
We describe a matter-wave amplifier for vibrational ground state molecules,
which uses a Feshbach resonance to first form quasi-bound molecules starting
from an atomic Bose-Einstein condensate. The quasi-bound molecules are then
driven into their stable vibrational ground state via a two-photon Raman
transition inside an optical cavity. The transition from the quasi-bound state
to the electronically excited state is driven by a classical field.
Amplification of ground state molecules is then achieved by using a strongly
damped cavity mode for the transition from the electronically excited molecules
to the molecular ground state
Optimal conversion of Bose condensed atoms into molecules via a Feshbach resonance
In many experiments involving conversion of quantum degenerate atomic gases
into molecular dimers via a Feshbach resonance, an external magnetic field is
linearly swept from above the resonance to below resonance. In the adiabatic
limit, the fraction of atoms converted into molecules is independent of the
functional form of the sweep and is predicted to be 100%. However, for
non-adiabatic sweeps through resonance, Landau-Zener theory predicts that a
linear sweep will result in a negligible production of molecules. Here we
employ a genetic algorithm to determine the functional time dependence of the
magnetic field that produces the maximum number of molecules for sweep times
that are comparable to the period of resonant atom-molecule oscillations,
. The optimal sweep through resonance indicates that
more than 95% of the atoms can be converted into molecules for sweep times as
short as while the linear sweep results in a
conversion of only a few percent. We also find that the qualitative form of the
optimal sweep is independent of the strength of the two-body interactions
between atoms and molecules and the width of the resonance
A Molecular Micromaser
We show that photoassociation of fermionic atoms into bosonic molecules
inside an optical lattice can be described using a Jaynes-Cummings Hamiltonian
with a nonlinear detuning. Using this equivalence to the Jaynes-Cummings
dynamics, we show how one can construct a micromaser for the molecular field in
each lattice site
Phase Conjugation of a Quantum-Degenerate Atomic Fermi Beam
We discuss the possibility of phase-conjugation of an atomic Fermi field via
nonlinear wave mixing in an ultracold gas. It is shown that for a beam of
fermions incident on an atomic phase-conjugate mirror, a time reversed backward
propagating fermionic beam is generated similar to the case in nonlinear
optics. By adopting an operational definition of the phase, we show that it is
possible to infer the presence of the phase-conjugate field by the loss of the
interference pattern in an atomic interferometer
Spin current and shot noise from a quantum dot coupled to a quantized cavity field
We examine the spin current and the associated shot noise generated in a
quantum dot connected to normal leads with zero bias voltage across the dot.
The spin current is generated by spin flip transitions induced by a quantized
electromagnetic field inside a cavity with one of the Zeeman states lying below
the Fermi level of the leads and the other above. In the limit of strong
Coulomb blockade, this model is analogous to the Jaynes-Cummings model in
quantum optics. We also calculate the photon current and photon current shot
noise resulting from photons leaking out of the cavity. We show that the photon
current is equal to the spin current and that the spin current can be
significantly larger than for the case of a classical driving field as a result
of cavity losses. In addition to this, the frequency dependent spin (photon)
current shot noise show dips (peaks) that are a result of the discrete nature
of photons
Quantum bistability and spin current shot noise of a single quantum dot coupled to an optical microcavity
Here we explore spin dependent quantum transport through a single quantum dot
coupled to an optical microcavity. The spin current is generated by electron
tunneling between a single doped reservoir and the dot combined with intradot
spin flip transitions induced by a quantized cavity mode. In the limit of
strong Coulomb blockade, this model is analogous to the Jaynes-Cummings model
in quantum optics and generates a pure spin current in the absence of any
charge current. Earlier research has shown that in the classical limit where a
large number of such dots interact with the cavity field, the spin current
exhibits bistability as a function of the laser amplitude that drives the
cavity. We show that in the limit of a single quantum dot this bistability
continues to be present in the intracavity photon statistics. Signatures of the
bistable photon statistics manifest themselves in the frequency dependent shot
noise of the spin current despite the fact that the quantum mechanical average
spin current no longer exhibits bistability. Besides having significance for
future quantum dot based optoelectronic devices, our results shed light on the
relation between bistability, which is traditionally viewed as a classical
effect, and quantum mechanics
Feshbach-resonance-induced atomic filamentation and quantum pair correlation in atom-laser-beam propagation
We study the propagation of an atom laser beam through a spatial region with
a magnetic field tuned to a Feshbach resonance. Tuning the magnetic field below
the resonance produces an effective focusing Kerr medium that causes a
modulational instability of the atomic beam. Under appropriate circumstances,
this results in beam breakup and filamentation seeded by quasi-particle
fluctuations, and in the generation of correlated atomic pairs
Noise limits in matter-wave interferometry using degenerate quantum gases
We analyze the phase resolution limit of a Mach-Zehnder atom interferometer
whose input consists of degenerate quantum gases of either bosons or fermions.
For degenerate gases, the number of atoms within one de Broglie wavelength is
larger than unity, so that atom-atom interactions and quantum statistics are no
longer negligible. We show that for equal atom numbers, the phase resolution
achievable with fermions is noticeably better than for interacting bosons.Comment: 4 pages, 5 figure
Two-fermion bound state in a Bose-Einstein condensate
A nonlinear Schr\"odinger equation is derived for the dynamics of a beam of
ultracold fermionic atoms traversing a Bose-Einstein condensate. The condensate
phonon modes are shown to provide a nonlinear medium for the fermionic atoms. A
two-fermion bound state is predicted to arise, and the signature of the bound
state in a nonlinear atom optics experiment is discussed.Comment: 4 pages, 1 figure