9 research outputs found
Collisional Aspects of Bosonic and Fermionic Dipoles in Quasi-Two-Dimensional Confining Geometries
Fundamental aspects of ultracold collisions between identical bosonic or
fermionic dipoles are studied under quasi-two-dimensional (Q2D) confinement. In
the strongly dipolar regime, bosonic and fermion species are found to share
important collisional properties as a result of the confining geometry, which
suppresses the inelastic rates irrespective of the quantum statistics obeyed. A
potential negative is that the confinement causes dipole-dipole resonances to
be extremely narrow, which could make it difficult to explore Q2D dipolar gases
with tunable interactions. Such properties are shown to be universal, and a
simple WKB model reproduces most of our numerical results. In order to shed
light on the many-body behavior of dipolar gases in Q2D we have analyzed the
scattering amplitude and developed an energy-analytic form of the
pseudopotentials for dipoles. For specific values of the dipolar interaction,
the pseudopotential coefficient can be tuned to arbitrarily large values,
indicating the possibility of realizing Q2D dipolar gases with tunable
interactions.Comment: 4.1 pages, 3 figure
Dynamics of three-body correlations in quenched unitary Bose gases
We investigate dynamical three-body correlations in the Bose gas during the
earliest stages of evolution after a quench to the unitary regime. The
development of few-body correlations is theoretically observed by determining
the two- and three-body contacts. We find that the growth of three-body
correlations is gradual compared to two-body correlations. The three-body
contact oscillates coherently, and we identify this as a signature of Efimov
trimers. We show that the growth of three-body correlations depends
non-trivially on parameters derived from both the density and Efimov physics.
These results demonstrate the violation of scaling invariance of unitary
bosonic systems via the appearance of log-periodic modulation of three-body
correlations
Ultracold molecular collisions in magnetic fields: Efficient incorporation of hyperfine structure in the total rotational angular momentum representation
The effects of hyperfine structure on ultracold molecular collisions in
external fields are largely unexplored due to major computational challenges
associated with rapidly proliferating hyperfine and rotational channels coupled
by highly anisotropic intermolecular interactions. We explore a new basis set
for incorporating the effects of hyperfine structure and external magnetic
fields in quantum scattering calculations on ultracold molecular collisions.
The basis is composed of direct products of the eigenfunctions of the total
{\it rotational} angular momentum (TRAM) of the collision complex and the
electron/nuclear spin basis functions of the collision partners. The separation
of the rotational and spin degrees of freedom ensures rigorous conservation of
even in the presence of external magnetic fields and isotropic hyperfine
interactions. The resulting block-diagonal structure of the scattering
Hamiltonian enables coupled-channel calculations on highly anisotropic
atom-molecule and molecule-molecule collisions to be performed independently
for each value of , with an added advantage of eliminating the unphysical
states present in the total angular momentum representation. We illustrate the
efficiency of the TRAM basis by calculating state-to-state cross sections for
ultracold He + YbF collisions in a magnetic field. The size of the TRAM basis
required to reach numerical convergence is 8 times smaller than that of the
uncoupled basis used previously, providing a computational gain of three orders
of magnitude. The TRAM basis is therefore well suited for rigorous quantum
scattering calculations on ultracold molecular collisions in the presence of
hyperfine interactions and external magnetic fields
Observation of unitary p-wave interactions between fermions in an optical lattice
Exchange-antisymmetric pair wavefunctions in fermionic systems can give rise to unconventional superconductors and superfluids with non-trivial transport properties. The realisation of these states in controllable quantum systems, such as ultracold gases, could enable new types of quantum simulations, topological quantum gates, and exotic few-body states. However, p-wave and other antisymmetric interactions are weak in naturally occurring systems, and their enhancement via Feshbach resonances in ultracold systems has been limited by three-body loss. In this work, we create isolated pairs of spin-polarised fermionic atoms in a multi-orbital three-dimensional optical lattice. We spectroscopically measure elastic p-wave inter- action energies of strongly interacting pairs of atoms near a magnetic Feshbach resonance, and find pair lifetimes to be up to fifty times larger than in free space. We demonstrate that on-site inter- action strengths can be widely tuned by the magnetic field and confinement strength, but collapse onto a universal single-parameter curve when rescaled by the harmonic energy and length scales of a single lattice site. Since three-body processes are absent within our approach, we are able to observe elastic unitary p-wave interactions for the first time. We take the first steps towards coherent temporal control via Rabi oscillations between free-atom and interacting-pair states. All experimental observations are compared both to an exact solution for two harmonically confined atoms interacting via a p-wave pseudopotential, and to numerical solutions using an ab-initio interaction potential. The understanding and control of on-site p-wave interactions provides a necessary component for the assembly of multi-orbital lattice models, and a starting point for investigations of how to protect such a system from three-body recombination even in the presence of weak tunnelling, for instance using Pauli blocking and lattice engineering. This combination will open a path for the exploration of new states of matter and many-body phenomena enabled by elastic p-wave interactions.Physic