Spinning a superfluid quantum gas with a state selective optical paddle

In our lab, we cool clouds of rubidium toms to ultra-cold temperatures. At such temperatures, they undergo a phase-transition to a Bose-Einstein condensate (BEC), a macroscopic occupation of a single quantum state, with many fascinating properties, including coherence, and superfluidity (flow without dissipation). We then trap this cloud of atoms in a ring geometry, formed from laser light, making a waveguide for the superfluid quantum gas to flow in. Using radio frequency pulses of magnetic field, we can flip the spin of the atoms, making 2 or more BECs of different spin states, and hence multiple superfluids with differing magnetic properties and interactions.

This project will experimentally and theoretically explore using spin-dependent optical potentials at "tune-out" wavelengths on a BEC of 87Rb confined in a ring shaped trap. At these wavelengths (which for 87Rb is at 790 nm), the scalar light shift contributions from the D1 (795 nm) and D2 line (780 nm) cancel. However, higher order terms (vectorial shifts) depend on the light polarization and the spin-state of the atom. The light field be seen as a repulsive barrier for one spin state, but invisible for the other. We will apply these potentials to BECs prepared in two spin states, and attempt to stir one spin component while not disturbing the other. This will allowing us to explore such effects as superfluid drag between different superfluids, a phenomena which has not yet been observed in nature.

BEC Lab, Centre of Excellence for Engineered Quantum Systems (EQUS).