195 research outputs found
Magnetically tuned spin dynamics resonance
We present the experimental observation of a magnetically tuned resonance
phenomenon resulting from spin mixing dynamics of ultracold atomic gases. In
particular we study the magnetic field dependence of spin conversion in F=2
87Rb spinor condensates in the crossover from interaction dominated to
quadratic Zeeman dominated dynamics. We discuss the observed phenomenon in the
framework of spin dynamics as well as matter wave four wave mixing. Furthermore
we show that the validity range of the single mode approximation for spin
dynamics is significantly extended in the regime of high magnetic field
Ultracold quantum gases in triangular optical lattices
Over the last years the exciting developments in the field of ultracold atoms
confined in optical lattices have led to numerous theoretical proposals devoted
to the quantum simulation of problems e.g. known from condensed matter physics.
Many of those ideas demand for experimental environments with non-cubic lattice
geometries. In this paper we report on the implementation of a versatile
three-beam lattice allowing for the generation of triangular as well as
hexagonal optical lattices. As an important step the superfluid-Mott insulator
(SF-MI) quantum phase transition has been observed and investigated in detail
in this lattice geometry for the first time. In addition to this we study the
physics of spinor Bose-Einstein condensates (BEC) in the presence of the
triangular optical lattice potential, especially spin changing dynamics across
the SF-MI transition. Our results suggest that below the SF-MI phase
transition, a well-established mean-field model describes the observed data
when renormalizing the spin-dependent interaction. Interestingly this opens new
perspectives for a lattice driven tuning of a spin dynamics resonance occurring
through the interplay of quadratic Zeeman effect and spin-dependent
interaction. We finally discuss further lattice configurations which can be
realized with our setup.Comment: 19 pages, 7 figure
Optical frequency generation using fiber Bragg grating filters for applications in portable quantum sensing
A method for the agile generation of the optical frequencies required for
laser cooling and atom interferometry of rubidium is demonstrated. It relies on
fiber Bragg grating technology to filter the output of an electro-optic
modulator and was demonstrated in a robust, alignment-free, single-seed,
frequency-doubled, telecom fiber laser system. The system was capable of 50 ns
frequency switching over a ~40 GHz range, ~0.5 W output power and amplitude
modulation with a ~15 ns rise/fall time and an extinction ratio of 120 2
dB. The technology is ideal for enabling high-bandwidth, mobile industrial and
space applications of quantum technologies
Localization of bosonic atoms by fermionic impurities in a 3d optical lattice
We observe a localized phase of ultracold bosonic quantum gases in a
3-dimensional optical lattice induced by a small contribution of fermionic
atoms acting as impurities in a Fermi-Bose quantum gas mixture. In particular
we study the dependence of this transition on the fermionic 40K impurity
concentration by a comparison to the corresponding superfluid to Mott insulator
transition in a pure bosonic 87Rb gas and find a significant shift in the
transition parameter. The observed shift is larger than expected based on a
mean-field argument, which is a strong indication that disorder-related effects
play a significant role.Comment: 4 pages, 4 figure
Do mixtures of bosonic and fermionic atoms adiabatically heat up in optical lattices?
Mixtures of bosonic and fermionic atoms in optical lattices provide a
promising arena to study strongly correlated systems. In experiments realizing
such mixtures in the quantum degenerate regime the temperature is a key
parameter. In this work, we investigate the intrinsic heating and cooling
effects due to an entropy-preserving raising of the optical lattice potential.
We analyze this process, identify the generic behavior valid for a wide range
of parameters, and discuss it quantitatively for the recent experiments with
87Rb and 40K atoms. In the absence of a lattice, we treat the bosons in the
Hartree-Fock-Bogoliubov-Popov-approximation, including the fermions in a
self-consistent mean field interaction. In the presence of the full
three-dimensional lattice, we use a strong coupling expansion. As a result of
the presence of the fermions, the temperature of the mixture after the lattice
ramp-up is always higher than for the pure bosonic case. This sheds light onto
a key point in the analysis of recent experiments.Comment: 5 pages, 3 figure
Ultracold heteronuclear molecules in a 3D optical lattice
We report on the creation of ultracold heteronuclear molecules assembled from
fermionic 40K and bosonic 87Rb atoms in a 3D optical lattice. Molecules are
produced at a heteronuclear Feshbach resonance both on the attractive and the
repulsive side of the resonance. We precisely determine the binding energy of
the heteronuclear molecules from rf spectroscopy across the Feshbach resonance.
We characterize the lifetime of the molecular sample as a function of magnetic
field and measure between 20 and 120ms. The efficiency of molecule creation via
rf association is measured and is found to decrease as expected for more deeply
bound molecules.Comment: 4 pages, 4 figure
Comfort-oriented control strategies for decentralized ventilation using co-simulation
Mechanical ventilation systems have acquired relevance in the past years in order to guarantee the hygrothermal comfort and indoor air quality (IAQ) in highly retrofitted residential buildings. The optimization of control strategies could provide a solution to this existing trade-off between energy efficiency, hygrothermal comfort and IAQ. In this publication, we propose a co-simulation approach (using EnergyPlus and Modelica) and a mathematical approximation of the discomfort of the occupant (namely, quadratic for relative humidity and exponential for CO2), and apply them to a demand controlled ventilation (DCV) scheme. Results show that this approach provides around 10% energy savings, while improving the thermal comfort, without compromising the humidity comfort or the IAQ. Finally, the developed functions could allow the control schemes to adapt to different occupant preferences, showing potential for future work
Evolution of a spinor condensate: coherent dynamics, dephasing and revivals
We present measurements and a theoretical model for the interplay of spin
dependent interactions and external magnetic fields in atomic spinor
condensates. We highlight general features like quadratic Zeeman dephasing and
its influence on coherent spin mixing processes by focusing on a specific
coherent superposition state in a F=1 Rb Bose-Einstein condensate. In
particular, we observe the transition from coherent spinor oscillations to
thermal equilibration
Long-Term Stability of an Area-Reversible Atom-Interferometer Sagnac Gyroscope
We report on a study of the long-term stability and absolute accuracy of an
atom interferometer gyroscope. This study included the implementation of an
electro-optical technique to reverse the vector area of the interferometer for
reduced systematics and a careful study of systematic phase shifts. Our data
strongly suggests that drifts less than 96 deg/hr are possible after
empirically removing shifts due to measured changes in temperature, laser
intensity, and several other experimental parameters.Comment: 4 pages, 4 figures, submitted to PR
Phase-fluctuating 3D condensates in elongated traps
We find that in very elongated 3D trapped Bose gases, even at temperatures
far below the BEC transition temperature Tc, the equilibrium state will be a 3D
condensate with fluctuating phase (quasicondensate). At sufficiently low
temperatures the phase fluctuations are suppressed and the quasicondensate
turns into a true condensate. The presence of the phase fluctuations allows for
extending thermometry of Bose-condensed gases well below those established in
current experiments.Comment: 5 pages REVTeX, 3 figures, misprints correcte
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