31 research outputs found
A lattice of double wells for manipulating pairs of cold atoms
We describe the design and implementation of a 2D optical lattice of double
wells suitable for isolating and manipulating an array of individual pairs of
atoms in an optical lattice. Atoms in the square lattice can be placed in a
double well with any of their four nearest neighbors. The properties of the
double well (the barrier height and relative energy offset of the paired sites)
can be dynamically controlled. The topology of the lattice is phase stable
against phase noise imparted by vibrational noise on mirrors. We demonstrate
the dynamic control of the lattice by showing the coherent splitting of atoms
from single wells into double wells and observing the resulting double-slit
atom diffraction pattern. This lattice can be used to test controlled neutral
atom motion among lattice sites and should allow for testing controlled
two-qubit gates.Comment: 9 pages, 11 figures Accepted for publication in Physical Review
Preparing and probing atomic number states with an atom interferometer
We describe the controlled loading and measurement of number-squeezed states
and Poisson states of atoms in individual sites of a double well optical
lattice. These states are input to an atom interferometer that is realized by
symmetrically splitting individual lattice sites into double wells, allowing
atoms in individual sites to evolve independently. The two paths then
interfere, creating a matter-wave double-slit diffraction pattern. The time
evolution of the double-slit diffraction pattern is used to measure the number
statistics of the input state. The flexibility of our double well lattice
provides a means to detect the presence of empty lattice sites, an important
and so far unmeasured factor in determining the purity of a Mott state
Sublattice addressing and spin-dependent motion of atoms in a double-well lattice
We load atoms into every site of an optical lattice and selectively spin flip
atoms in a sublattice consisting of every other site. These selected atoms are
separated from their unselected neighbors by less than an optical wavelength.
We also show spin-dependent transport, where atomic wave packets are coherently
separated into adjacent sites according to their internal state. These tools
should be useful for quantum information processing and quantum simulation of
lattice models with neutral atoms
Probing the relaxation towards equilibrium in an isolated strongly correlated 1D Bose gas
The problem of how complex quantum systems eventually come to rest lies at
the heart of statistical mechanics. The maximum entropy principle put forward
in 1957 by E. T. Jaynes suggests what quantum states one should expect in
equilibrium but does not hint as to how closed quantum many-body systems
dynamically equilibrate. A number of theoretical and numerical studies
accumulate evidence that under specific conditions quantum many-body models can
relax to a situation that locally or with respect to certain observables
appears as if the entire system had relaxed to a maximum entropy state. In this
work, we report the experimental observation of the non-equilibrium dynamics of
a density wave of ultracold bosonic atoms in an optical lattice in the regime
of strong correlations. Using an optical superlattice, we are able to prepare
the system in a well-known initial state with high fidelity. We then follow the
dynamical evolution of the system in terms of quasi-local densities, currents,
and coherences. Numerical studies based on the time-dependent density-matrix
renormalization group method are in an excellent quantitative agreement with
the experimental data. For very long times, all three local observables show a
fast relaxation to equilibrium values compatible with those expected for a
global maximum entropy state. We find this relaxation of the quasi-local
densities and currents to initially follow a power-law with an exponent being
significantly larger than for free or hardcore bosons. For intermediate times
the system fulfills the promise of being a dynamical quantum simulator, in that
the controlled dynamics runs for longer times than present classical algorithms
based on matrix product states can efficiently keep track of.Comment: 8 pages, 6 figure
Double-Well Optical Lattices with Atomic Vibrations and Mesoscopic Disorder
Double-well optical lattice in an insulating state is considered. The
influence of atomic vibrations and mesoscopic disorder on the properties of the
lattice are studied. Vibrations lead to the renormalization of atomic
interactions. The occurrence of mesoscopic disorder results in the appearance
of first-order phase transitions between the states with different levels of
atomic imbalance. The existence of a nonuniform external potential, such as
trapping potential, essentially changes the lattice properties, suppressing the
disorder fraction and rising the transition temperature.Comment: Latex file, 21 pages, 2 figure
Single atom quantum walk with 1D optical superlattices
A proposal for the implementation of quantum walks using cold atom technology
is presented. It consists of one atom trapped in time varying optical
superlattices. The required elements are presented in detail including the
preparation procedure, the manipulation required for the quantum walk evolution
and the final measurement. These procedures can be, in principle, implemented
with present technology.Comment: 6 pages, 7 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
Artificial gauge fields for the Bose-Hubbard model on a checkerboard superlattice and extended Bose-Hubbard model
We study the effects of an artificial gauge field on the ground-state phases
of the Bose-Hubbard model on a checkerboard superlattice in two dimensions,
including the superfluid phase and the Mott and alternating Mott insulators.
First, we discuss the single-particle Hofstadter problem, and show that the
presence of a checkerboard superlattice gives rise to a magnetic
flux-independent energy gap in the excitation spectrum. Then, we consider the
many-particle problem, and derive an analytical mean-field expression for the
superfluid-Mott and superfluid--alternating-Mott insulator phase transition
boundaries. Finally, since the phase diagram of the Bose-Hubbard model on a
checkerboard superlattice is in many ways similar to that of the extended
Bose-Hubbard model, we comment on the effects of magnetic field on the latter
model, and derive an analytical mean-field expression for the
superfluid-insulator phase transition boundaries as well.Comment: 8 pages, 5 figures and 1 table; to appear in EPJ
Interferometry with independent Bose-Einstein ondensates: parity as an EPR/Bell quantum variable
When independent Bose-Einstein condensates (BEC), described quantum
mechanically by Fock (number) states, are sent into interferometers, the
measurement of the output port at which the particles are detected provides a
binary measurement, with two possible results . With two interferometers
and two BEC's, the parity (product of all results obtained at each
interferometer) has all the features of an Einstein-Podolsky-Rosen quantity,
with perfect correlations predicted by quantum mechanics when the settings
(phase shifts of the interferometers) are the same. When they are different,
significant violations of Bell inequalities are obtained. These violations do
not tend to zero when the number of particles increases, and can therefore
be obtained with arbitrarily large systems, but a condition is that all
particles should be detected. We discuss the general experimental requirements
for observing such effects, the necessary detection of all particles in
correlation, the role of the pixels of the CCD detectors, and that of the
alignments of the interferometers in terms of matching of the wave fronts of
the sources in the detection regions. Another scheme involving three
interferometers and three BEC's is discussed; it leads to Greenberger Horne
Zeilinger (GHZ) sign contradictions, as in the usual GHZ case with three
particles, but for an arbitrarily large number of them. Finally,
generalizations of the Hardy impossibilities to an arbitrarily large number of
particles are introduced. BEC's provide a large versality for observing
violations of local realism in a variety of experimental arrangements.Comment: appendix adde