55 research outputs found
Optical detection of a BCS transition of Lithium-6 in harmonic traps
We study the detection of a BCS transition within a sample of Lithium--6
atoms confined in a harmonic trap. Using the local density approximation we
calculate the pair correlation function in the normal and superfluid state at
zero temperature. We show that the softening of the Fermi hole associated with
a BCS transition leads to an observable increase in the intensity of
off--resonant light scattered from the atomic cloud at small angles.Comment: 7 pages, 3 figures, submitted to Europhysics Letter
Cavity cooling of a nanomechanical resonator by light scattering
We present a novel method for opto-mechanical cooling of sub-wavelength sized
nanomechanical resonators. Our scheme uses a high finesse Fabry-Perot cavity of
small mode volume, within which the nanoresonator is acting as a
position-dependant perturbation by scattering. In return, the back-action
induced by the cavity affects the nanoresonator dynamics and can cool its
fluctuations. We investigate such cavity cooling by scattering for a nanorod
structure and predict that ground-state cooling is within reach.Comment: 4 pages, 3 figure
A Carbon Nanofilament-Bead Necklace
Carbon nanofilaments with carbon beads grown on their surfaces were successfully synthesized reproducibly by a floating catalyst CVD method. The nanofilaments hosting the pearl-like structures typically show an average diameter of about 60 nm, which mostly consists of low-ordered graphite layers. The beads with diameter range 150−450 nm are composed of hundreds of crumpled and random graphite layers. The mechanism for the formation of these beaded nanofilaments is ascribed to two nucleation processes of the pyrolytic carbon deposition, arising from a temperature gradient between different parts of the reaction chamber. Furthermore, the Raman scattering properties of the beaded nanofilaments have been measured, as well as their confocal Raman G-line images. The Raman spectra reveal that that the trunks of the nanofilaments have better graphitic properties than the beads, which is consistent with the HRTEM analysis. The beaded nanofilaments are expected to have high potential applications in composites, which should exhibit both particle- and fiber-reinforcing functions for the host matrixes
Laser-induced collective excitations in a two-component Fermi gas
We consider the linear density response of a two-component (superfluid) Fermi
gas of atoms when the perturbation is caused by laser light. We show that
various types of laser excitation schemes can be transformed into linear
density perturbations, however, a Bragg spectroscopy scheme is needed for
transferring energy and momentum into a collective mode. This makes other types
of laser probing schemes insensitive for collective excitations and therefore
well suited for the detection of the superfluid order parameter. We show that
for the special case when laser light is coupled between the two components of
the Fermi gas, density response is always absent in a homogeneous system.Comment: 6 pages, no figure
Lattice-Gas Simulations of Minority-Phase Domain Growth in Binary Immiscible and Ternary Amphiphilic Fluid
We investigate the growth kinetics of binary immiscible fluids and emulsions
in two dimensions using a hydrodynamic lattice-gas model. We perform
off-critical quenches in the binary fluid case and find that the domain size
within the minority phase grows algebraically with time in accordance with
theoretical predictions. In the late time regime we find a growth exponent n =
0.45 over a wide range of concentrations, in good agreement with other
simluations. In the early time regime we find no universal growth exponent but
a strong dependence on the concentration of the minority phase. In the ternary
amphiphilic fluid case the kinetics of self assembly of the droplet phase are
studied for the first time. At low surfactant concentrations, we find that,
after an early algebraic growth, a nucleation regime dominates the late-time
kinetics, which is enhanced by an increasing concentration of surfactant. With
a further increase in the concentration of surfactant, we see a crossover to
logarithmically slow growth, and finally saturation of the oil droplets, which
we fit phenomenologically to a stretched exponential function. Finally, the
transition between the droplet and the sponge phase is studied.Comment: 22 pages, 13 figures, submitted to PR
Signatures of resonance superfluidity in a quantum Fermi gas
In this letter, we predict a direct and observable signature of the
superfluid phase in a quantum Fermi gas, in a temperature regime already
accessible in current experiments. We apply the theory of resonance
superfluidity to a gas confined in a harmonic potential and demonstrate that a
significant increase in density will be observed in the vicinity of the trap
center.Comment: 4 pages, 4 figure
Laser probing of Cooper-paired trapped atoms
We consider a gas of trapped Cooper-paired fermionic atoms which are
manipulated by laser light. The laser induces a transition from an internal
state with large negative scattering length (superfluid) to one with weaker
interactions (normal gas). We show that the process can be used to detect the
presence of the superconducting order parameter. Also, we propose a direct way
of measuring the size of the gap in the trap. The efficiency and feasibility of
this probing method is investigated in detail in different physical situations.Comment: 9 pages, 8 figure
Vortices in superfluid trapped Fermi gases at zero temperature
We discuss various aspects of the vortex state of a dilute superfluid atomic
Fermi gas at T=0. The energy of the vortex in a trapped gas is calculated and
we provide an expression for the thermodynamic critical rotation frequency of
the trap for its formation. Furthermore, we propose a method to detect the
presence of a vortex by calculating the effect of its associated velocity field
on the collective mode spectrum of the gas
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