46 research outputs found
Quantum Noise Correlation Experiments with Ultracold Atoms
Noise correlation analysis is a detection tool for spatial structures and
spatial correlations in the in-trap density distribution of ultracold atoms. In
this book chapter, we discuss the implementation, properties and limitations of
the method applied to ensembles of ultracold atoms in optical lattices, and
describe some instances where it has been applied.Comment: 26 pages, 14 figures - To appear as Chapter 8 in "Quantum gas
experiments - exploring many-body states," P. T\"orm\"a, K. Sengstock, eds.
(Imperial College Press, to be published 2014
Localized magnetic moments with tunable spin exchange in a gas of ultracold fermions
We report on the experimental realization of a state-dependent lattice for a
two-orbital fermionic quantum gas with strong interorbital spin exchange. In
our state-dependent lattice, the ground and metastable excited electronic
states of Yb take the roles of itinerant and localized magnetic
moments, respectively. Repulsive on-site interactions in conjunction with the
tunnel mobility lead to spin exchange between mobile and localized particles,
modeling the coupling term in the well-known Kondo Hamiltonian. In addition, we
find that this exchange process can be tuned resonantly by varying the on-site
confinement. We attribute this to a resonant coupling to center-of-mass excited
bound states of one interorbital scattering channel
Phase coherence of an atomic Mott insulator
We investigate the phase coherence properties of ultracold Bose gases in
optical lattices, with special emphasis on the Mott insulating phase. We show
that phase coherence on short length scales persists even deep in the
insulating phase, preserving a finite visibility of the interference pattern
observed after free expansion. This behavior can be attributed to a coherent
admixture of particle/hole pairs to the perfect Mott state for small but finite
tunneling. In addition, small but reproducible ``kinks'' are seen in the
visibility, in a broad range of atom numbers. We interpret them as signatures
for density redistribution in the shell structure of the trapped Mott
insulator
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
Direct probing of the Mott crossover in the SU() Fermi-Hubbard model
The Fermi-Hubbard model (FHM) is a cornerstone of modern condensed matter
theory. Developed for interacting electrons in solids, which typically exhibit
SU() symmetry, it describes a wide range of phenomena, such as metal to
insulator transitions and magnetic order. Its generalized SU()-symmetric
form, originally applied to multi-orbital materials such as transition-metal
oxides, has recently attracted much interest owing to the availability of
ultracold SU()-symmetric atomic gases. Here we report on a detailed
experimental investigation of the SU()-symmetric FHM using local probing of
an atomic gas of ytterbium in an optical lattice to determine the equation of
state through different interaction regimes. We prepare a low-temperature
SU()-symmetric Mott insulator and characterize the Mott crossover,
representing important steps towards probing predicted novel SU()-magnetic
phases
Quantum Spin Dynamics of Mode-Squeezed Luttinger Liquids in Two-Component Atomic Gases
We report on the observation of the phase dynamics of interacting
one-dimensional ultracold bosonic gases with two internal degrees of freedom.
By controlling the non-linear atomic interactions close to a Feshbach resonance
we are able to induce a phase diffusive many-body spin dynamics. We monitor
this dynamical evolution by Ramsey interferometry, supplemented by a novel,
many-body echo technique. We find that the time evolution of the system is well
described by a Luttinger liquid initially prepared in a multimode squeezed
state. Our approach allows us to probe the non-equilibrium evolution of
one-dimensional many-body quantum systems.Comment: 4 pages, 3 figures Updated version, minor change
Coherent collisional spin dynamics in optical lattices
We report on the observation of coherent, purely collisionally driven spin
dynamics of neutral atoms in an optical lattice. For high lattice depths, atom
pairs confined to the same lattice site show weakly damped Rabi-type
oscillations between two-particle Zeeman states of equal magnetization, induced
by spin changing collisions. This paves the way towards the efficient creation
of robust entangled atom pairs in an optical lattice. Moreover, measurement of
the oscillation frequency allows for precise determination of the spin-changing
collisional coupling strengths, which are directly related to fundamental
scattering lengths describing interatomic collisions at ultracold temperatures.Comment: revised version; 4 pages, 5 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
Recommended from our members
A Quantum Gas Microscope for Detecting Single Atoms in a Hubbard-Regime Optical Lattice
Recent years have seen tremendous progress in creating complex atomic many-body quantum systems. One approach is to use macroscopic, effectively thermodynamic ensembles of ultracold atoms to create quantum gases and strongly correlated states of matter, and to analyze the bulk properties of the ensemble. For example, bosonic and fermionic atoms in a Hubbard regime optical lattice 1, 2, 3, 4, 5 allow experimenters to carry out quantum simulations of solid state models 6, thereby addressing fundamental questions of condensed matter physics. The opposite approach is to build up microscopic quantum systems atom by atom – with complete control over all degrees of freedom 7, 8, 9. The atoms or ions act as qubits and allow experimenters to realize quantum gates with the goal of creating highly controllable quantum information systems. Until now, the macroscopic and microscopic strategies have been fairly disconnected. Here, we present a “quantum gas microscope” that bridges the two approaches, realizing a system where atoms of a macroscopic ensemble are detected individually and a complete set of degrees of freedom of each of them is determined through preparation and measurement. By implementing a high-resolution optical imaging system, single atoms are detected with near-unity fidelity on individual sites of a Hubbard regime optical lattice. The lattice itself is generated by projecting a holographic mask through the imaging system. It has an arbitrary geometry, chosen to support both strong tunnel coupling between lattice sites and strong on-site
confinement. On one hand, this new approach can be used to directly detect strongly correlated states of matter. In the context of condensed matter simulation, this corresponds to the detection of individual electrons in the simulated crystal with atomic resolution. On
the other hand, the quantum gas microscope opens the door for the addressing and readout of large-scale quantum information systems with ultracold atoms.Physic