479 research outputs found
Ultracold Metastable Calcium Ensembles, a Medium for Matter Wave Amplification ?
We propose an experimental implementation of matter wave amplification by
optical pumping (MAO) with metastable calcium atoms. First experimental results
indicate that pumping rates can be significantly higher than in previous
experimental schemes and let it appear promising that the threshold condition
for generation of degeneracy can be reached.Comment: 6 pages, 2 PS figure
Reducing the linewidth of a diode laser below 30 Hz by stabilization to a reference cavity with finesse above 10^5
An extended cavity diode laser operating in the Littrow configuration
emitting near 657 nm is stabilized via its injection current to a reference
cavity with a finesse of more than 10^5 and a corresponding resonance linewidth
of 14 kHz. The laser linewidth is reduced from a few MHz to a value below 30
Hz. The compact and robust setup appears ideal for a portable optical frequency
standard using the Calcium intercombination line.Comment: 8 pages, 4 figures on 3 additional pages, corrected version,
submitted to Optics Letter
High-order optical nonlinearity at low light levels
We observe a nonlinear optical process in a gas of cold atoms that
simultaneously displays the largest reported fifth-order nonlinear
susceptibility \chi^(5) = 1.9x10^{-12} (m/V)^4 and high transparency. The
nonlinearity results from the simultaneous cooling and crystallization of the
gas, and gives rise to efficient Bragg scattering in the form of
six-wave-mixing at low-light-levels. For large atom-photon coupling strengths,
the back-action of the scattered fields influences the light-matter dynamics.
This system may have important applications in many-body physics, quantum
information processing, and multidimensional soliton formation.Comment: 5 pages, 3 figure
Orbital superfluidity in the -band of a bipartite optical square lattice
The successful emulation of the Hubbard model in optical lattices has
stimulated world wide efforts to extend their scope to also capture more
complex, incompletely understood scenarios of many-body physics. Unfortunately,
for bosons, Feynmans fundamental "no-node" theorem under very general
circumstances predicts a positive definite ground state wave function with
limited relevance for many-body systems of interest. A promising way around
Feynmans statement is to consider higher bands in optical lattices with more
than one dimension, where the orbital degree of freedom with its intrinsic
anisotropy due to multiple orbital orientations gives rise to a structural
diversity, highly relevant, for example, in the area of strongly correlated
electronic matter. In homogeneous two-dimensional optical lattices, lifetimes
of excited bands on the order of a hundred milliseconds are possible but the
tunneling dynamics appears not to support cross-dimensional coherence. Here we
report the first observation of a superfluid in the -band of a bipartite
optical square lattice with -orbits and -orbits arranged in a
chequerboard pattern. This permits us to establish full cross-dimensional
coherence with a life-time of several ten milliseconds. Depending on a small
adjustable anisotropy of the lattice, we can realize real-valued striped
superfluid order parameters with different orientations or a
complex-valued order parameter, which breaks time reversal
symmetry and resembles the -flux model proposed in the context of high
temperature superconductors. Our experiment opens up the realms of orbital
superfluids to investigations with optical lattice models.Comment: 5 pages, 5 figure
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