Observation of superfluid current through a dissipative quantum point contact

We experimentally and theoretically confirm the robustness of fermionic superfluidity to spin-dependent particle dissipation in a unitary Fermi gas. By locally illuminating a quantum point contact connecting two superfluid reservoirs with a beam resonant with one of the two spin states, we engineer particle loss and measure its effect on the signature of superfluidity in our system: a non-Ohmic supercurrent carried by multiple Andreev reflections (MAR). We develop a mean-field model in the Keldysh formalism that quantitatively reproduces our observations. We find that there is no critical dissipation strength where the supercurrent vanishes. Instead, it smoothly decays towards zero with increasing dissipation, indicating a surprising robustness of MAR. Our model also predicts that Onsager's reciprocal relations are violated due to broken detailed balance, which we hope to soon experimentally confirm as it can have significant implications for dissipative engineering of transport properties.