81 research outputs found
Bose-Einstein condensates in 1D optical lattices: nonlinearity and Wannier-Stark spectra
We present our experimental investigations on the subject of
nonlinearity-modified Bloch-oscillations and of nonlinear Landau-Zener
tunneling between two energy bands in a rubidium Bose Einstein condensate in an
accelerated periodic potential. Nonlinearity introduces an asymmetry in
Landau-Zener tunneling. We also present measurements of resonantly enhanced
tunneling between the Wannier-Stark energy levels for Bose-Einstein condensates
loaded into an optical lattice.Comment: Chapter of "Nonlinearities of Periodic Structures and Metamaterials"
(edited by C. Denz, S. Flach, and Yu. Kivshar) to be published by Springe
Four-level N-scheme crossover resonances in Rb saturation spectroscopy in magnetic fields
We perform saturated absorption spectroscopy on the D line for room
temperature rubidium atoms immersed in magnetic fields within the 0.05-0.13 T
range. At those medium-high field values the hyperfine structure in the excited
state is broken by the Zeeman effect, while in the ground state hyperfine
structure and Zeeman shifts are comparable. The observed spectra are composed
by a large number of absorption lines. We identify them as saturated
absorptions on two-level systems, on three-level systems in a V configuration
and on four-level systems in a N or double-N configuration where two optical
transitions not sharing a common level are coupled by spontaneous emission
decays. We analyze the intensity of all those transitions within a unified
simple theoretical model. We concentrate our attention on the double-N
crossovers signals whose intensity is very large because of the symmetry in the
branching ratios of the four levels. We point out that these structures,
present in all alkali atoms at medium-high magnetic fields, have interesting
properties for electromagnetically induced transparency and slow light
applications.Comment: Submitted to Physical Review
Ultracold Rubidium atoms excited to Rydberg levels
Ultracold atomic gases excited to strongly interacting Rydberg states are a promising system for quantum simulations of many-body systems. The dipole blockade of Rydberg excitations is a hallmark of the strong interactions between atoms in these high-lying quantum states. We have measured the Rydberg excitation for rubidium ultracold atoms in magneto-optical traps and for Bose-Einstein condensates loaded into quasi one-dimensional traps. One of the consequences of the dipole blockade is the suppression of fluctuations in the counting statistics of Rydberg excitations. We have obtained experimental results on the dynamics and the counting statistics of Rydberg excitations of ultra-cold Rubidium atoms both on and off resonance, which exhibit sub- and super-Poissonian counting statistics, respectively. We have found strongly bimodal counting distributions in the offresonant regime
Unearthing wave-function renormalization effects in the time evolution of a Bose-Einstein condensate
We study the time evolution of a Bose-Einstein condensate in an accelerated
optical lattice. When the condensate has a narrow quasimomentum distribution
and the optical lattice is shallow, the survival probability in the ground band
exhibits a steplike structure. In this regime we establish a connection between
the wave-function renormalization parameter and the phenomenon of
resonantly enhanced tunneling.Comment: 12 pages, 3 figures. arXiv admin note: substantial text overlap with
arXiv:1201.628
Exploring dynamic localization with a Bose-Einstein condensate
We report on the experimental observation of dynamic localization of a
Bose-Einstein condensate in a shaken optical lattice, both for sinusoidal and
square-wave forcing. The formulation of this effect in terms of a quasienergy
band collapse, backed by the excellent agreement of the observed collapse
points with the theoretical predictions, suggests the feasibility of systematic
quasienergy band engineering.Comment: 7 pages, 4 figure
Analysis of ring laser gyroscopes including laser dynamics
Inertial sensors stimulate very large interest, not only for their
application but also for fundamental physics tests. Ring laser gyros, which
measure angular rotation rate, are certainly among the most sensitive inertial
sensors, with excellent dynamic range and bandwidth. Large area ring laser
gyros are routinely able to measure fractions of prad/s, with high duty cycle
and bandwidth, providing fast, direct and local measurement of relevant
geodetic and geophysical signals. Improvements of a factor would open
the windows for general relativity tests, as the GINGER project, an Earth based
experiment aiming at the Lense-Thirring test at level. However, it is
well known that the dynamics of the laser induces non-linearities, and those
effects are more evident in small scale instruments. Sensitivity and accuracy
improvements are always worthwhile, and in general there is demand for high
sensitivity environmental study and development of inertial platforms, where
small scale transportable instruments should be used. We discuss a novel
technique to analyse the data, aiming at studying and removing those
non-linearity. The analysis is applied to the two ring laser prototypes GP2 and
GINGERINO, and angular rotation rate evaluated with the new and standard
methods are compared. The improvement is evident, it shows that the
back-scatter problem of the ring laser gyros is negligible with a proper
analysis of the data, improving the performances of large scale ring laser
gyros, but also indicating that small scale instruments with sensitivity of
nrad/s are feasible.Comment: 9 pages and 7 figure
Seeded excitation avalanches in off-resonantly driven Rydberg gases
We report an experimental investigation of the facilitated excitation
dynamics in off-resonantly driven Rydberg gases by separating the initial
off-resonant excitation phase from the facilitation phase, in which successive
facilitation events lead to excitation avalanches. We achieve this by creating
a controlled number of initial seed excitations. Greater insight into the
avalanche mechanism is obtained from an analysis of the full counting
distributions. We also present simple mathematical models and numerical
simulations of the excitation avalanches that agree well with our experimental
results.Comment: 13 pages, 6 figure
Pulsed high magnetic field measurement via a Rubidium vapor sensor
We present a new technique to measure pulsed magnetic fields based on the use
of Rubidium in gas phase as a metrological standard. We have therefore
developed an instrument based on laser inducing transitions at about 780~nm (D2
line) in a Rubidium gas contained in a mini-cell of 3~mm~x~3~mm cross section.
To be able to insert such a cell in a standard high field pulsed magnet we have
realized a fibred probe kept at a fixed temperature. Transition frequencies for
both the (light polarization parallel to the magnetic field) and
(light polarization perpendicular to the magnetic field) configurations are
measured by a commercial wavemeter. One innovation of our sensor is that in
addition of monitoring the light transmitted by the Rb cell, which is usual, we
also monitor the fluorescence emission of the gas sample from a very small
volume with the advantage of reducing the impact of the field inhomogeneity on
the field measurement. Our sensor has been tested up to about 58~T.Comment: Submitted to Review Scientific Instrument
Model and phase-diagram analysis of photothermal instabilities in an optomechanical resonator
A study of the phototermal instabilities in a Fabry-Perot cavity is reported, where one mirror consists of a silicon-nitride membrane coated by the molecular organic semiconductor tris(8-hydroxyquinoline) aluminum and silver layers. We propose a theoretical model to describe the back-action associated with the delayed response of the cavity field to the radiation pressure force and the photothermal force. For the case under investigation, the photothermal force response occurs on a timescale that is comparable to that of mirror oscillations and dominates over the radiation pressure force. A phase diagram analysis has been performed to map the stability of the static solution as a function of the control parameters. The model equations are integrated numerically and the time history is compared to experimental measurements of the transmitted field and displacement of the membrane. In both experimental and theoretical data we observe large amplitude oscillations when the cavity length is scanned at a low speed compared to the growth rate of the instability. The perturbation is found to evolve through three regimes: sinusoidal oscillations, double peaks and single peaks followed by a lethargic regime. When the cavity length is scanned in opposite directions, dynamical hysteresis is observed, whose extension has a power law dependence on the scanning rate
Alq3 coated silicon nanomembranes for cavity optomechanics
The optomechanical properties of a silicon-nitride membrane mirror covered by Alq3 and Silver layers are investigated. Excitation at two laser wavelengths, 780 and 405 nm, corresponding to different absorptions of the multilayer, is examined. Such dual driving will lead to a more flexible optomechanical operation. Topographic reconstruction of the whole static membrane deformation and cooling of the membrane oscillations are reported. The cooling, observed for blue laser detuning and produced by bolometric forces, is deduced from the optomechanical damping of the membrane eigenfrequency. We determine the presence of different contributions to the photothermal response of the membrane
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