27 research outputs found
Electromagnetically Induced Transparency and Light Storage in an Atomic Mott Insulator
We experimentally demonstrate electromagnetically induced transparency and
light storage with ultracold 87Rb atoms in a Mott insulating state in a three
dimensional optical lattice. We have observed light storage times of about 240
ms, to our knowledge the longest ever achieved in ultracold atomic samples.
Using the differential light shift caused by a spatially inhomogeneous far
detuned light field we imprint a "phase gradient" across the atomic sample,
resulting in controlled angular redirection of the retrieved light pulse.Comment: 4 pages, 4 figure
Time-resolved Observation and Control of Superexchange Interactions with Ultracold Atoms in Optical Lattices
Quantum mechanical superexchange interactions form the basis of quantum
magnetism in strongly correlated electronic media. We report on the direct
measurement of superexchange interactions with ultracold atoms in optical
lattices. After preparing a spin-mixture of ultracold atoms in an
antiferromagnetically ordered state, we measure a coherent
superexchange-mediated spin dynamics with coupling energies from 5 Hz up to 1
kHz. By dynamically modifying the potential bias between neighboring lattice
sites, the magnitude and sign of the superexchange interaction can be
controlled, thus allowing the system to be switched between antiferromagnetic
or ferromagnetic spin interactions. We compare our findings to predictions of a
two-site Bose-Hubbard model and find very good agreement, but are also able to
identify corrections which can be explained by the inclusion of direct
nearest-neighbor interactions.Comment: 24 pages, 7 figure
Single Particle Tunneling in Strongly Driven Double Well Potentials
We report on the first direct observation of coherent control of single
particle tunneling in a strongly driven double well potential. In our setup
atoms propagate in a periodic arrangement of double wells allowing the full
control of the driving parameters such as frequency, amplitude and even the
space-time symmetry. Our experimental findings are in quantitative agreement
with the predictions of the corresponding Floquet theory and are also compared
to the predictions of a simple two mode model. Our experiments reveal directly
the critical dependence of coherent destruction of tunneling on the generalized
parity symmetry.Comment: 4 pages, 5 figure
Counting atoms using interaction blockade in an optical superlattice
We report on the observation of an interaction blockade effect for ultracold
atoms in optical lattices, analogous to Coulomb blockade observed in mesoscopic
solid state systems. When the lattice sites are converted into biased double
wells, we detect a discrete set of steps in the well population for increasing
bias potentials. These correspond to tunneling resonances where the atom number
on each side of the barrier changes one by one. This allows us to count and
control the number of atoms within a given well. By evaluating the amplitude of
the different plateaus, we can fully determine the number distribution of the
atoms in the lattice, which we demonstrate for the case of a superfluid and
Mott insulating regime of 87Rb.Comment: 4 pages, 4 figure
The equation of state of ultracold Bose and Fermi gases: a few examples
We describe a powerful method for determining the equation of state of an
ultracold gas from in situ images. The method provides a measurement of the
local pressure of an harmonically trapped gas and we give several applications
to Bose and Fermi gases. We obtain the grand-canonical equation of state of a
spin-balanced Fermi gas with resonant interactions as a function of
temperature. We compare our equation of state with an equation of state
measured by the Tokyo group, that reveals a significant difference in the
high-temperature regime. The normal phase, at low temperature, is well
described by a Landau Fermi liquid model, and we observe a clear thermodynamic
signature of the superfluid transition. In a second part we apply the same
procedure to Bose gases. From a single image of a quasi ideal Bose gas we
determine the equation of state from the classical to the condensed regime.
Finally the method is applied to a Bose gas in a 3D optical lattice in the Mott
insulator regime. Our equation of state directly reveals the Mott insulator
behavior and is suited to investigate finite-temperature effects.Comment: 14 pages, 6 figure
Expansion of a quantum gas released from an optical lattice
We analyze the interference pattern produced by ultracold atoms released from
an optical lattice. Such interference patterns are commonly interpreted as the
momentum distributions of the trapped quantum gas. We show that for finite
time-of-flights the resulting density distribution can, however, be
significantly altered, similar to a near-field diffraction regime in optics. We
illustrate our findings with a simple model and realistic quantum Monte Carlo
simulations for bosonic atoms, and compare the latter to experiments.Comment: 5 pages, 3 figure
Topological phase transitions in the non-Abelian honeycomb lattice
Ultracold Fermi gases trapped in honeycomb optical lattices provide an
intriguing scenario, where relativistic quantum electrodynamics can be tested.
Here, we generalize this system to non-Abelian quantum electrodynamics, where
massless Dirac fermions interact with effective non-Abelian gauge fields. We
show how in this setup a variety of topological phase transitions occur, which
arise due to massless fermion pair production events, as well as pair
annihilation events of two kinds: spontaneous and strongly-interacting induced.
Moreover, such phase transitions can be controlled and characterized in optical
lattice experiments.Comment: RevTex4 file, color figure
Towards high-speed optical quantum memories
Quantum memories, capable of controllably storing and releasing a photon, are
a crucial component for quantum computers and quantum communications. So far,
quantum memories have operated with bandwidths that limit data rates to MHz.
Here we report the coherent storage and retrieval of sub-nanosecond low
intensity light pulses with spectral bandwidths exceeding 1 GHz in cesium
vapor. The novel memory interaction takes place via a far off-resonant
two-photon transition in which the memory bandwidth is dynamically generated by
a strong control field. This allows for an increase in data rates by a factor
of almost 1000 compared to existing quantum memories. The memory works with a
total efficiency of 15% and its coherence is demonstrated by directly
interfering the stored and retrieved pulses. Coherence times in hot atomic
vapors are on the order of microsecond - the expected storage time limit for
this memory.Comment: 13 pages, 5 figure
Thermometry with spin-dependent lattices
We propose a method for measuring the temperature of strongly correlated
phases of ultracold atom gases confined in spin-dependent optical lattices. In
this technique, a small number of "impurity" atoms--trapped in a state that
does not experience the lattice potential--are in thermal contact with atoms
bound to the lattice. The impurity serves as a thermometer for the system
because its temperature can be straightforwardly measured using time-of-flight
expansion velocity. This technique may be useful for resolving many open
questions regarding thermalization in these isolated systems. We discuss the
theory behind this method and demonstrate proof-of-principle experiments,
including the first realization of a 3D spin-dependent lattice in the strongly
correlated regime.Comment: 22 pages, 8 figures v2: Several references added; Section on heating
rates updated to include dipole fluctuation terms; Section added on the
limitations of the proposed method. To appear in New Journal of Physic
Entanglement of spin waves among four quantum memories
Quantum networks are composed of quantum nodes that interact coherently by
way of quantum channels and open a broad frontier of scientific opportunities.
For example, a quantum network can serve as a `web' for connecting quantum
processors for computation and communication, as well as a `simulator' for
enabling investigations of quantum critical phenomena arising from interactions
among the nodes mediated by the channels. The physical realization of quantum
networks generically requires dynamical systems capable of generating and
storing entangled states among multiple quantum memories, and of efficiently
transferring stored entanglement into quantum channels for distribution across
the network. While such capabilities have been demonstrated for diverse
bipartite systems (i.e., N=2 quantum systems), entangled states with N > 2 have
heretofore not been achieved for quantum interconnects that coherently `clock'
multipartite entanglement stored in quantum memories to quantum channels. Here,
we demonstrate high-fidelity measurement-induced entanglement stored in four
atomic memories; user-controlled, coherent transfer of atomic entanglement to
four photonic quantum channels; and the characterization of the full
quadripartite entanglement by way of quantum uncertainty relations. Our work
thereby provides an important tool for the distribution of multipartite
entanglement across quantum networks.Comment: 4 figure