1,000 research outputs found
Collisional oscillations of trapped boson-fermion mixtures approaching collapse
We study the collective modes of a confined gaseous cloud of bosons and
fermions with mutual attractive interactions at zero temperature. The cloud
consists of a Bose-Einstein condensate and a spin-polarized Fermi gas inside a
spherical harmonic trap and the coupling between the two species is varied by
increasing either the magnitude of the interspecies s-wave scattering length or
the number of bosons. The mode frequencies are obtained in the collisional
regime by solving the equations of generalized hydrodynamics and are compared
with the spectra calculated in the collisionless regime within a random-phase
approximation. We find that, as the mixture is driven towards the collapse
instability, the frequencies of the modes of fermionic origin show a blue shift
which can become very significant for large numbers of bosons. Instead the
modes of bosonic origin show a softening, which becomes most pronounced in the
very proximity of collapse. Explicit illustrations of these trends are given
for the monopolar spectra, but similar trends are found for the dipolar and
quadrupolar spectra except for the surface (n=0) modes which are essentially
unaffected by the interactions.Comment: 9 pages, 5 figures, revtex
From an insulating to a superfluid pair-bond liquid
We study an exchange coupled system of itinerant electrons and localized
fermion pairs resulting in a resonant pairing formation. This system inherently
contains resonating fermion pairs on bonds which lead to a superconducting
phase provided that long range phase coherence between their constituents can
be established. The prerequisite is that the resonating fermion pairs can
become itinerant. This is rendered possible through the emergence of two kinds
of bond-fermions: individual and composite fermions made of one individual
electron attached to a bound pair on a bond. If the strength of the exchange
coupling exceeds a certain value, the superconducting ground state undergoes a
quantum phase transition into an insulating pair-bond liquid state. The gap of
the superfluid phase thereby goes over continuously into a charge gap of the
insulator. The change-over from the superconducting to the insulating phase is
accompanied by a corresponding qualitative modification of the dispersion of
the two kinds of fermionic excitations. Using a bond operator formalism, we
derive the phase diagram of such a scenario together with the elementary
excitations characterizing the various phases as a function of the exchange
coupling and the temperature.Comment: 10 pages, 5 figure
Proton-tetraneutron elastic scattering
We analyze the elastic scattering of protons on a 4n system. This was used as
part of the detection technique of a recent experiment [1] to search for the 4n
(tetraneutron) as a bound particle. We show that it is unlikely that this
process alone could yield the events reported in ref. [1], unless the 4n has an
anomalously large backward elastic scattering amplitude.Comment: 6 pages, 2 figures, accepted for publication in Phys. Rev.
Measurement of interaction energy near a Feshbach resonance in a 6Li Fermi gas
We investigate the strongly interacting regime in an optically trapped Li
Fermi mixture near a Feshbach resonance. The resonance is found at G
in good agreement with theory. Anisotropic expansion of the gas is interpreted
by collisional hydrodynamics. We observe an unexpected and large shift (G)
between the resonance peak and both the maximum of atom loss and the change of
sign of the interaction energy.Comment: 4 pages, 4 figure
Solvable relativistic quantum dots with vibrational spectra
For Klein-Gordon equation a consistent physical interpretation of wave
functions is reviewed as based on a proper modification of the scalar product
in Hilbert space. Bound states are then studied in a deep-square-well model
where spectrum is roughly equidistant and where a fine-tuning of the levels is
mediated by PT-symmetric interactions composed of imaginary delta functions
which mimic creation/annihilation processes.Comment: Int. Worskhop "Pseudo-Hermitian Hamiltonians in Quantum Physics III"
(June 20 - 22, 2005, Koc Unversity,
Istanbul(http://home.ku.edu.tr/~amostafazadeh/workshop/workshop.htm) a part
of talk (9 pages
Adiabatic Fidelity for Atom-Molecule Conversion in a Nonlinear Three-Level \Lambda-system
We investigate the dynamics of the population transfer for atom-molecule
three-level -system on stimulated Raman adiabatic passage(STIRAP). We
find that the adiabatic fidelity for the coherent population trapping(CPT)
state or dark state, as the function of the adiabatic parameter, approaches to
unit in a power law. The power exponent however is much less than the
prediction of linear adiabatic theorem. We further discuss how to achieve
higher adiabatic fidelity for the dark state through optimizing the external
parameters of STIRAP. Our discussions are helpful to gain higher atom-molecule
conversion yield in practical experiments.Comment: 4 pages, 5 figure
New method for extracting quasi-bound states from the continuum
A new parameter-free method is proposed for treatment of single-particle
resonances in the real-energy continuum shell model. This method yields
quasi-bound states embedded in the continuum which provide a natural
generalization of weakly bound single-particle states.Comment: 22 pages, 10 figure
Control of Ultra-cold Inelastic Collisions by Feshbash Resonances and Quasi-One-Dimensional Confinement
Cold inelastic collisions of atoms or molecules are analyzed using very
general arguments. In free space, the deactivation rate can be enhanced or
suppressed together with the scattering length of the corresponding elastic
collision via a Feshbach resonance, and by interference of deactivation of the
closed and open channels. In reduced dimensional geometries, the deactivation
rate decreases with decreasing collision energy and does not increase with
resonant elastic scattering length. This has broad implications; e.g.,
stabilization of molecules in a strongly confining two-dimensional optical
lattice, since collisional decay of the highly vibrationally excited states due
to inelastic collisions is suppressed. The relation of our results with those
based on the Lieb-Liniger model are addressed.Comment: 5 pages, 1 figur
Irreversible quantum graphs
Irreversibility is introduced to quantum graphs by coupling the graphs to a
bath of harmonic oscillators. The interaction which is linear in the harmonic
oscillator amplitudes is localized at the vertices. It is shown that for
sufficiently strong coupling, the spectrum of the system admits a new continuum
mode which exists even if the graph is compact, and a {\it single} harmonic
oscillator is coupled to it. This mechanism is shown to imply that the quantum
dynamics is irreversible. Moreover, it demonstrates the surprising result that
irreversibility can be introduced by a "bath" which consists of a {\it single}
harmonic oscillator
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