Research
SEED Project
Ultracold Trapped Atoms
Faculty: C. Chin, K. Levin,
This Seed is based on the premise that the study and control of ultracold fermionic atoms represents a new and important direction in the evolution of materials physics. These new ''materials'' have much in common with nano-scale or quantum dots. Both will allow condensed matter physicists to study basic problems in correlated fermionic systems. The atomic traps like the dots contain of the order of 105 atoms. What is unique about trapped atoms is the capability to tune (via application of magnetic fields) the strength of the particle interaction from weakly to strongly interacting. With the introduction of optical lattices, formed by the interference pattern of laser beams, it will be possible to further simulate solid state lattice systems, and address important, unsolved questions on, for example, Hubbard-type model Hamiltonians.
Our previous work in this exciting field has been involved with the gas
phase where we have studied experimentally as well as theoretically the
crossover from BCS to Bose Einstein condensation (BEC) [Phys. Rev. Lett.
92, 120401 (2004), and Physics Reports, 412,
1, 2005] the character of the pairing gap [Science 305,
1128 (2004), and PRA 72, 011602(R) (2005) via
RF spectroscopy] as well as the thermodynamical properties of these trapped
gases [Science, 305, 1128 (2004)]. The focus of
our effort during the last year has been on polarized gases [Phys. Rev.
Lett. 97, 090402 (2006), for example].
Our work will next move on to theoretical and experimental studies of optical
lattices. Theoretically, we will be focusing on fermionic atomic systems
in which the on-site attraction and the inter-site hopping can be associated
with an attractive (3d) Hubbard Hamiltonian. We plan to investigate superconductor-insulator(SI)
transitions in this system. We find these transitions appear at sufficiently
large filling fraction and for sufficiently large on-site attraction |U|.
This transition may be related to the SI transition (which appears in the
underdoped regime) in the high temperature superconductors. We will determine
the nature of the insulating state and its associated ordering (charge density
wave, Wigner crystal of pairs, pair density wave, etc.). In a parallel manner
our experiments are working towards constructing optical lattices of (bosonic)
Cs atoms in order to study the (bosonic) Mott insulator-superconductor transition.
Additionally, we plan to explore both theoretically and experimentally quantum
gases of fermions with large dipolar interactions. We will synthesize dipolar
molecules with a large dipole moment by pairing one bosonic cesium atom
and one fermionic lithium atom in an optical lattice. Both atom species
will be spin-polarized to the lowest internal state to guarantee the stability
of the molecules. The molecules thus prepared are fermionic and are expected
to form a stable, degenerate Fermi gas at low temperatures. Based on this
system we will have access to an entirely new form of matter, a superfluid
with long range dipolar interaction
From annual report to the NSF, March 2007