47 research outputs found
Dynamical vanishing of the order parameter in a fermionic condensate
We analyze the dynamics of a condensate of ultra-cold atomic fermions
following an abrupt change of the pairing strength. At long times, the system
goes to a non-stationary steady state, which we determine exactly. The
superfluid order parameter asymptotes to a constant value. We show that the
order parameter vanishes when the pairing strength is decreased below a certain
critical value. In this case, the steady state of the system combines
properties of normal and superfluid states - the gap and the condensate
fraction vanish, while the superfluid density is nonzero.Comment: 4 pages, 3 figures, journal versio
Atom-molecule coexistence and collective dynamics near a Feshbach resonance of cold fermions
Degenerate Fermi gas interacting with molecules near Feshbach resonance is
unstable with respect to formation of a mixed state in which atoms and
molecules coexist as a coherent superposition. Theory of this state is
developed using a mapping to the Dicke model, treating molecular field in the
single mode approximation. The results are accurate in the strong coupling
regime relevant for current experimental efforts. The exact solution of the
Dicke model is exploited to study stability, phase diagram, and nonadiabatic
dynamics of molecular field in the mixed state.Comment: 5 pages, 2 figure
Coexistence of superfluid and Mott phases of lattice bosons
Recent experiments on strongly-interacting bosons in optical lattices have
revealed the co-existence of spatially-separated Mott-insulating and
number-fluctuating phases. The description of this inhomogeneous situation is
the topic of this Letter. We establish that the number-fluctuating phase forms
a superfluid trapped between the Mott-insulating regions and derive the
associated collective mode structure. We discuss the interlayer's crossover
between two- and three-dimensional behavior as a function of the lattice
parameters and estimate the critical temperatures for the transition of the
superfluid phase to a normal phase
Synchronization in the BCS Pairing Dynamics as a Critical Phenomenon
Fermi gas with time-dependent pairing interaction hosts several different
dynamical states. Coupling between the collective BCS pairing mode and
individual Cooper pair states can make the latter either synchronize or
dephase. We describe transition from phase-locked undamped oscillations to
Landau-damped dephased oscillations in the collisionless, dissipationless
regime as a function of coupling strength. In the dephased regime, we find a
second transition at which the long-time asymptotic pairing amplitude vanishes.
Using a combination of numerical and analytical methods we establish a
continuous (type II) character of both transitions
Resonant Bend Loss in Leakage Channel Fibers
Leakage channel fibers, designed to suppress higher-order modes, demonstrate
resonant power loss at certain critical radii of curvature. Outside the
resonance, the power recovers to the levels offset by the usual mechanism of
bend-induced loss. Using C-imaging, we experimentally characterize this
anomaly and identify the corresponding physical mechanism as the radiative
decay of the fundamental mode mediated by the resonant coupling to a cladding
mode.Comment: 3 pages, 4 figures, submitted to Optics Letter