823 research outputs found
Dynamic Kosterlitz-Thouless transition in 2D Bose mixtures of ultra-cold atoms
We propose a realistic experiment to demonstrate a dynamic
Kosterlitz-Thouless transition in ultra-cold atomic gases in two dimensions.
With a numerical implementation of the Truncated Wigner Approximation we
simulate the time evolution of several correlation functions, which can be
measured via matter wave interference. We demonstrate that the relaxational
dynamics is well-described by a real-time renormalization group approach, and
argue that these experiments can guide the development of a theoretical
framework for the understanding of critical dynamics.Comment: 5 pages, 6 figure
Unconventional Spin Density Waves in Dipolar Fermi Gases
The conventional spin density wave (SDW) phase (Overhauser, 1962), as found
in antiferromagnetic metal for example (Fawcett 1988), can be described as a
condensate of particle-hole pairs with zero angular momentum, ,
analogous to a condensate of particle-particle pairs in conventional
superconductors. While many unconventional superconductors with Cooper pairs of
finite have been discovered, their counterparts, density waves with
non-zero angular momenta, have only been hypothesized in two-dimensional
electron systems (Nayak, 2000). Using an unbiased functional renormalization
group analysis, we here show that spin-triplet particle-hole condensates with
emerge generically in dipolar Fermi gases of atoms (Lu, Burdick, and
Lev, 2012) or molecules (Ospelkaus et al., 2008; Wu et al.) on optical lattice.
The order parameter of these exotic SDWs is a vector quantity in spin space,
and, moreover, is defined on lattice bonds rather than on lattice sites. We
determine the rich quantum phase diagram of dipolar fermions at half-filling as
a function of the dipolar orientation, and discuss how these SDWs arise amidst
competition with superfluid and charge density wave phases.Comment: 5 pages, 3 figure
Detecting paired and counterflow superfluidity via dipole oscillations
We suggest an experimentally feasible procedure to observe paired and
counterflow superfluidity in ultra-cold atom systems. We study the time
evolution of one-dimensional mixtures of bosonic atoms in an optical lattice
following an abrupt displacement of an additional weak confining potential. We
find that the dynamic responses of the paired superfluid phase for attractive
inter-species interactions and the counterflow superfluid phase for repulsive
interactions are qualitatively distinct and reflect the quasi long-range order
that characterizes these states. These findings suggest a clear experimental
procedure to detect these phases, and give an intuitive insight into their
dynamics.Comment: 4 pages,5 figure
Intrinsic Photoconductivity of Ultracold Fermions in Optical Lattices
We report on the experimental observation of an analog to a persistent
alternating photocurrent in an ultracold gas of fermionic atoms in an optical
lattice. The dynamics is induced and sustained by an external harmonic
confinement. While particles in the excited band exhibit long-lived
oscillations with a momentum dependent frequency a strikingly different
behavior is observed for holes in the lowest band. An initial fast collapse is
followed by subsequent periodic revivals. Both observations are fully explained
by mapping the system onto a nonlinear pendulum.Comment: 5+7 pages, 4+4 figure
Phase fluctuations in anisotropic Bose condensates: from cigars to rings
We study the phase-fluctuating condensate regime of ultra-cold atoms trapped
in a ring-shaped trap geometry, which has been realized in recent experiments.
We first consider a simplified box geometry, in which we identify the
conditions to create a state that is dominated by thermal phase-fluctuations,
and then explore the experimental ring geometry. In both cases we demonstrate
that the requirement for strong phase fluctuations can be expressed in terms of
the total number of atoms and the geometric length scales of the trap only. For
the ring-shaped trap we discuss the zero temperature limit in which a
condensate is realized where the phase is fluctuating due to interactions and
quantum fluctuations. We also address possible ways of detecting the phase
fluctuating regime in ring condensates.Comment: 10 pages, 5 figures, minor edit
Metastable order protected by destructive many-body interference
The phenomenon of metastability can shape dynamical processes on all temporal
and spatial scales. Here, we induce metastable dynamics by pumping ultracold
bosonic atoms from the lowest band of an optical lattice to an excitation band,
via a sudden quench of the unit cell. The subsequent relaxation process to the
lowest band displays a sequence of stages, which include a metastable stage,
during which the atom loss from the excitation band is strongly suppressed.
Using classical-field simulations and analytical arguments, we provide an
explanation for this experimental observation, in which we show that the
transient condensed state of the atoms in the excitation band is a dark state
with regard to collisional decay and tunneling to a low-energy orbital.
Therefore the metastable state is stabilized by destructive interference due to
the chiral phase pattern of the condensed state. Our experimental and
theoretical study provides a detailed understanding of the different stages of
a paradigmatic example of many-body relaxation dynamics
- …