56 research outputs found
Mechanisms of superconductivity investigated by nuclear radiation
Investigation focused on the behavior of superconducting magnet and its constituent materials during and after exposure to nuclear radiation. The results will indicate the feasibility of their use in diverse applications and various environments
Bichromatic Driving of a Solid State Cavity QED System
The bichromatic driving of a solid state cavity quantum electrodynamics
system is used to probe cavity dressed state transitions and observe coherent
interaction between the system and the light field. We theoretically
demonstrate the higher order cavity-dressed states, supersplitting, and AC
stark shift in a solid state system comprised of a quantum dot strongly coupled
to a photonic crystal cavity for on- and far off-resonant cases. For the
off-resonant case, phonons mediate off-resonant coupling between the quantum
dot and the photonic resonator, a phenomenon unique to solid state cavity
quantum electrodynamics.Comment: 8 pages 6 figure
Strong Coupling Theory of Two Level Atoms in Periodic Fields
We present a new convergent strong coupling expansion for two-level atoms in
external periodic fields, free of secular terms. As a first application, we
show that the coherent destruction of tunnelling is a third-order effect. We
also present an exact treatment of the high-frequency region, and compare it
with the theory of averaging. The qualitative frequency spectrum of the
transition probability amplitude contains an effective Rabi frequency.Comment: 4 pages with 3 figure
Microwave Spectroscopy of Cold Rubidium Atoms
The effect of microwave radiation on the resonance fluorescence of a cloud of
cold atoms in a magnetooptical trap is studied. The radiation
frequency was tuned near the hyperfine splitting frequency of rubidium atoms in
the 5S ground state. The microwave field induced magnetic dipole transitions
between the magnetic sublevels of the 5S(F=2) and 5S(F=3) states, resulting in
a change in the fluorescence signal. The resonance fluorescence spectra were
recorded by tuning the microwave radiation frequency. The observed spectra were
found to be substantially dependent on the transition under study and the
frequency of a repump laser used in the cooling scheme.Comment: 6 pages, 4 figure
Band Gaps for Atoms in Light based Waveguides
The energy spectrum for a system of atoms in a periodic potential can exhibit
a gap in the band structure. We describe a system in which a laser is used to
produce a mechanical potential for the atoms, and a standing wave light field
is used to shift the atomic levels using the Autler-Townes effect, which
produces a periodic potential. The band structure for atoms guided by a hollow
optical fiber waveguide is calculated in three dimensions with quantised
external motion. The size of the band gap is controlled by the light guided by
the fiber. This variable band structure may allow the construction of devices
which can cool atoms. The major limitation on this device would be the
spontaneous emission losses.Comment: 7 pages, four postscript figures, uses revtex.sty, available through
http://online.anu.edu.au/Physics/papers/atom.htm
Quasienergy Spectroscopy of Excitons
We theoretically study nonlinear optics of excitons under intense THz
irradiation. In particular, the linear near infrared absorption and resonantly
enhanced nonlinear sideband generation are described. We predict a rich
structure in the spectra which can be interpreted in terms of the quasienergy
spectrum of the exciton, via a remarkably transparent expression for the
susceptibility, and show that the effects of strongly avoided quasienergy
crossings manifest themselves directly, both in the absorption and transmitted
sidebands.Comment: 4 pages RevTex, 3 eps figs included, as publishe
Anomalous Sliding Friction and Peak Effect near the Flux Lattice Melting Transition
Recent experiments have revealed a giant "peak effect" in ultrapure high
superconductors. Moreover, the new data show that the peak effect
coincides exactly with the melting transition of the underlying flux lattice.
In this work, we show using dynamical scaling arguments that the friction due
to the pinning centers acting on the flux lattice develops a singularity near a
continuous phase transition and can diverge for many systems. The magnitude of
the nonlinear sliding friction of the flux lattice scales with this atomistic
friction. Thus, the nonlinear conductance should diverge for a true continuous
transition in the flux lattice or peak at a weakly first order transition or
for systems of finite size.Comment: 4 pages, to appear in Phys. Rev.
Magnetic Pinning of Vortices in a Superconducting Film: The (anti)vortex-magnetic dipole interaction energy in the London approximation
The interaction between a superconducting vortex or antivortex in a
superconducting film and a magnetic dipole with in- or out-of-plane
magnetization is investigated within the London approximation. The dependence
of the interaction energy on the dipole-vortex distance and the film thickness
is studied and analytical results are obtained in limiting cases. We show how
the short range interaction with the magnetic dipole makes the co-existence of
vortices and antivortices possible. Different configurations with vortices and
antivortices are investigated.Comment: 12 pages, 12 figures. Submitted to Phys. Rev.
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