Momentum Space Realization of the d.c. Josephson Effect in Spin-Orbit Coupled BECs

Spin-orbit coupled BECs provide a highly flexible platform for the study of Josephson physics. A variety of Josephson effects can exist in systems consisting of two superconducting reservoirs separated by a weak link. In our experiments, we study the d.c. Josephson effect which describes a supercurrent that forms without a chemical potential difference (corresponding to an externally applied voltage in an analogous solid-state realization of a Josephson Junction). To experimentally realize momentum space Josephson physics, we employ a BEC with Raman generated spin-orbit coupling along with an optical lattice that facilitates momentum state tunneling between two band minima. Varying the detuning of the Raman lasers leads to shifts of the energies at the two band minima. A study of the supercurrent as a function of the detuning ramp speed can then be used to identify a critical value of the supercurrent, providing insights into the d.c. Josephson effect. The described system offers a novel experimental platform to utilize Josephson physics in the further application of quantum research. This work complements corresponding studies of the a.c. Josephson effect conducted by our group.