Phase-tunable Josephson junction and spontaneous mass current in a spin-orbit-coupled Fermi superfluid

Atomtronics has the potential for engineering new types of functional devices, such as Josephson junctions (JJs). Previous studies have mainly focused on JJs whose ground states have zero or π superconducting phase difference across the junctions, while arbitrary phase-tunable JJs may have important applications in superconducting electronics and quantum computation. Here we show that a phase-tunable JJ can be implemented in a spin-orbit-coupled cold atomic gas with the magnetic tunneling barrier generated by a spin-dependent focused laser beam. We consider the JJ confined in either a linear harmonic trap or a circular ring trap. In the ring trap, the magnetic barrier induces a spontaneous mass current for the ground state of the JJ, demonstrating the magnetoelectric effects of cold atoms.