998 research outputs found
Direct Measurement of intermediate-range Casimir-Polder potentials
We present the first direct measurements of Casimir-Polder forces between
solid surfaces and atomic gases in the transition regime between the
electrostatic short-distance and the retarded long-distance limit. The
experimental method is based on ultracold ground-state Rb atoms that are
reflected from evanescent wave barriers at the surface of a dielectric glass
prism. Our novel approach does not require assumptions about the potential
shape. The experimental data confirm the theoretical prediction in the
transition regime.Comment: 4 pages, 3 figure
Self-synchronization and dissipation-induced threshold in collective atomic recoil lasing
Networks of globally coupled oscillators exhibit phase transitions from incoherent to coherent states. Atoms interacting with the counterpropagating modes of a unidirectionally pumped high-finesse ring cavity form such a globally coupled network. The coupling mechanism is provided by collective atomic recoil lasing, i.e., cooperative Bragg scattering of laser light at an atomic density grating, which is self-induced by the laser light. Under the rule of an additional friction force, the atomic ensemble is expected to undergo a phase transition to a state of synchronized atomic motion. We present the experimental investigation of this phase transition by studying the threshold behavior of this lasing process
Ultra-cold atoms in an optical cavity: two-mode laser locking to the cavity avoiding radiation pressure
The combination of ultra-cold atomic clouds with the light fields of optical
cavities provides a powerful model system for the development of new types of
laser cooling and for studying cooperative phenomena. These experiments
critically depend on the precise tuning of an incident pump laser with respect
to a cavity resonance. Here, we present a simple and reliable experimental
tuning scheme based on a two-mode laser spectrometer. The scheme uses a first
laser for probing higher-order transversal modes of the cavity having an
intensity minimum near the cavity's optical axis, where the atoms are confined
by a magnetic trap. In this way the cavity resonance is observed without
exposing the atoms to unwanted radiation pressure. A second laser, which is
phase-locked to the first one and tuned close to a fundamental cavity mode
drives the coherent atom-field dynamics.Comment: 7 pages, 7 figure
Cavity-enhanced superradiant Rayleigh scattering with ultra-cold and Bose-Einstein condensed atoms
We report on the observation of collective atomic recoil lasing and
superradiant Rayleigh scattering with ultracold and Bose-Einstein condensed
atoms in an optical ring cavity. Both phenomena are based on instabilities
evoked by the collective interaction of light with cold atomic gases. This
publication clarifies the link between the two effects. The observation of
superradiant behavior with thermal clouds as hot as several tens of
proves that the phenomena are driven by the cooperative
dynamics of the atoms, which is strongly enhanced by the presence of the ring
cavity.Comment: 10 pages, 10 figure
Pinning Transition of Bose-Einstein Condensates in Optical Ring Resonators
We experimentally investigate the dynamic instability of Bose-Einstein
condensates in an optical ring resonator that is asymmetrically pumped in both
directions. We find that, beyond a critical resonator-pump detuning, the system
becomes stable regardless of the pump strength. Phase diagrams and quenching
curves are presented and described by numerical simulations. We discuss a
physical explanation based on a geometric interpretation of the underlying
nonlinear equations of motion.Comment: 4 pages, 4 figure
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