224 research outputs found
Particle correlations in a fermi superfluid
We discuss correlations between particles of different momentum in a
superfluid fermi gas, accessible through noise measurements of absorption
images of the expanded gas. We include two elements missing from the simplest
treatment, based on the BCS wavefunction: the explicit use of a conserving
approximation satisfying particle number conservation, and the inclusion of the
contribution from Cooper pairs at finite momentum. We expect the latter to be a
significant issue in the strongly correlated state emerging in the BCS-BEC
crossover.Comment: Published versio
Resonant control of spin dynamics in ultracold quantum gases by microwave dressing
We study experimentally interaction-driven spin oscillations in optical
lattices in the presence of an off-resonant microwave field. We show that the
energy shift induced by this microwave field can be used to control the spin
oscillations by tuning the system either into resonance to achieve near-unity
contrast or far away from resonance to suppress the oscillations. Finally, we
propose a scheme based on this technique to create a flat sample with either
singly- or doubly-occupied sites, starting from an inhomogeneous Mott
insulator, where singly- and doubly-occupied sites coexist.Comment: 4 pages, 5 figure
Observation of an orbital interaction-induced Feshbach resonance in 173-Yb
We report on the experimental observation of a novel inter-orbital Feshbach
resonance in ultracold 173-Yb atoms, which opens the possibility of tuning the
interactions between the 1S0 and 3P0 metastable state, both possessing
vanishing total electronic angular momentum. The resonance is observed at
experimentally accessible magnetic field strengths and occurs universally for
all hyperfine state combinations. We characterize the resonance in the bulk via
inter-orbital cross-thermalization as well as in a three-dimensional lattice
using high-resolution clock-line spectroscopy.Comment: 5 pages, 4 figure
Precision measurement of spin-dependent interaction strengths for spin-1 and spin-2 87Rb atoms
We report on precision measurements of spin-dependent interaction-strengths
in the 87Rb spin-1 and spin-2 hyperfine ground states. Our method is based on
the recent observation of coherence in the collisionally driven spin-dynamics
of ultracold atom pairs trapped in optical lattices. Analysis of the Rabi-type
oscillations between two spin states of an atom pair allows a direct
determination of the coupling parameters in the interaction hamiltonian. We
deduce differences in scattering lengths from our data that can directly be
compared to theoretical predictions in order to test interatomic potentials.
Our measurements agree with the predictions within 20%. The knowledge of these
coupling parameters allows one to determine the nature of the magnetic ground
state. Our data imply a ferromagnetic ground state for 87Rb in the f=1
manifold, in agreement with earlier experiments performed without the optical
lattice. For 87Rb in the f=2 manifold the data points towards an
antiferromagnetic ground state, however our error bars do not exclude a
possible cyclic phase.Comment: 11 pages, 5 figure
Preparation and detection of d-wave superfluidity in two-dimensional optical superlattices
We propose a controlled method to create and detect d-wave superfluidity with
ultracold fermionic atoms loaded in two-dimensional optical superlattices. Our
scheme consists in preparing an array of nearest-neighbor coupled square
plaquettes or ``superplaquettes'' and using them as building blocks to
construct a d-wave superfluid state. We describe how to use the coherent
dynamical evolution in such a system to experimentally probe the pairing
mechanism. We also derive the zero temperature phase diagram of the fermions in
a checkerboard lattice (many weakly coupled plaquettes) and show that by tuning
the inter-plaquette tunneling spin-dependently or varying the filling factor
one can drive the system into a d-wave superfluid phase or a Cooper pair
density wave phase. We discuss the use of noise correlation measurements to
experimentally probe these phases.Comment: 8 pages, 6 figure
Exploring the Kondo model in and out of equilibrium with alkaline-earth atoms
We propose a scheme to realize the Kondo model with tunable anisotropy using
alkaline-earth atoms in an optical lattice. The new feature of our setup is
Floquet engineering of interactions using time-dependent Zeeman shifts, that
can be realized either using state-dependent optical Stark shifts or magnetic
fields. The properties of the resulting Kondo model strongly depend on the
anisotropy of the ferromagnetic interactions. In particular, easy-plane
couplings give rise to Kondo singlet formation even though microscopic
interactions are all ferromagnetic. We discuss both equilibrium and dynamical
properties of the system that can be measured with ultracold atoms, including
the impurity spin susceptibility, the impurity spin relaxation rate, as well as
the equilibrium and dynamical spin correlations between the impurity and the
ferromagnetic bath atoms. We analyze the non-equilibrium time evolution of the
system using a variational non-Gaussian approach, which allows us to explore
coherent dynamics over both short and long timescales, as set by the bandwidth
and the Kondo singlet formation, respectively. In the quench-type experiments,
when the Kondo interaction is suddenly switched on, we find that real-time
dynamics shows crossovers reminiscent of poor man's renormalization group flow
used to describe equilibrium systems. For bare easy-plane ferromagnetic
couplings, this allows us to follow the formation of the Kondo screening cloud
as the dynamics crosses over from ferromagnetic to antiferromagnetic behavior.
On the other side of the phase diagram, our scheme makes it possible to measure
quantum corrections to the well-known Korringa law describing the temperature
dependence of the impurity spin relaxation rate. Theoretical results discussed
in our paper can be measured using currently available experimental techniques.Comment: 22 pages, 12 figure
Hybrid 2D surface trap for quantum simulation
We demonstrate a novel optical trapping scheme for ultracold atoms. Using a
combination of evanescent wave, standing wave, and magnetic potentials we
create a deeply 2D Bose-Einstein condensate (BEC) at a few microns from a glass
surface. Using techniques such as broadband "white" light to create evanescent
and standing waves, we realize a smooth potential with a trap frequency aspect
ratio of 300:1:1 and long lifetimes. This makes the setup suitable for
many-body quantum simulations and applications such as high precision
measurements close to surfaces.Comment: 5 pages, 4 figure
Cooling toolbox for atoms in optical lattices
We propose and analyze several schemes for cooling bosonic and fermionic
atoms in an optical lattice potential close to the ground state of the
no-tunnelling regime. Some of the protocols rely on the concept of algorithmic
cooling, which combines occupation number filtering with ideas from ensemble
quantum computation. We also design algorithms that create an ensemble of
defect-free quantum registers. We study the efficiency of our protocols for
realistic temperatures and in the presence of a harmonic confinement. We also
propose an incoherent physical implementation of filtering which can be
operated in a continuous way.Comment: 14 pages, 13 figure
Realization of a single Josephson junction for Bose-Einstein condensates
We report on the realization of a double-well potential for Rubidium-87
Bose-Einstein condensates. The experimental setup allows the investigation of
two different dynamical phenomena known for this system - Josephson
oscillations and self-trapping. We give a detailed discussion of the
experimental setup and the methods used for calibrating the relevant
parameters. We compare our experimental findings with the predictions of an
extended two-mode model and find quantitative agreement
Probing quantum phases of ultracold atoms in optical lattices by transmission spectra in cavity QED
Studies of ultracold atoms in optical lattices link various disciplines,
providing a playground where fundamental quantum many-body concepts, formulated
in condensed-matter physics, can be tested in much better controllable atomic
systems, e.g., strongly correlated phases, quantum information processing.
Standard methods to measure quantum properties of Bose-Einstein condensates
(BECs) are based on matter-wave interference between atoms released from traps
which destroys the system. Here we propose a nondestructive method based on
optical measurements, and prove that atomic statistics can be mapped on
transmission spectra of a high-Q cavity. This can be extremely useful for
studying phase transitions between Mott insulator and superfluid states, since
various phases show qualitatively distinct light scattering. Joining the
paradigms of cavity quantum electrodynamics (QED) and ultracold gases will
enable conceptually new investigations of both light and matter at ultimate
quantum levels, which only recently became experimentally possible. Here we
predict effects accessible in such novel setups.Comment: 6 pages, 3 figure
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