Interacting fermions under spin-orbit coupling
JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309-0440, USA
Engineered spin–orbit coupling (SOC) in cold atom systems can shed light to synthetic materials and complex condensed matter phenomena. We demonstrate that SOC between fermions can be engineered to occur naturally in an optical lattice clock. SOC is both generated and probed using a direct ultra-narrow optical clock transition between two electronic orbital states in 87Sr atoms. We use clock spectroscopy to prepare lattice band populations, internal electronic states and quasi-momenta, and to produce spin–orbit-coupled dynamics. The exceptionally long lifetime of the excited clock state eliminates decoherence and atom loss from spontaneous emission at all relevant experimental timescales, allowing subsequent momentum- and spin-resolved in-situ probing of the SOC band structure and eigenstates. We use these capabilities to study Bloch oscillations, spin–momentum locking and Van Hove singularities in the transition density of states. Furthermore, many-body correlations arising from the interplay of interactions and SOC have been observed recently.