Dark state transport between unitary Fermi superfluids

Abstract

The formation of dark states is an important concept in quantum sciences, but its compatibility with strong interparticle interactions -- for example, in a quantum degenerate gas -- is hardly explored. Here, we realize a dark state in one of the spins of a two-component, resonantly interacting Fermi gas using a $\Lambda$ system within the $D_2$ transitions of ${}^6$Li at high magnetic field. The dark state is created in a micrometer-sized region within a one-dimensional channel connecting two superfluid reservoirs. The particle transport between the reservoirs is used as a probe. We observe that atoms are transported in the dark state and the superfluid-assisted fast current is preserved. If the dark state resonant condition is not met, the transport is suppressed by the spontaneous emission. We also uncover an asymmetry in the transport timescale across the two-photon resonance, which is absent in the non-interacting regime and diminished at higher temperatures. This work raises questions on the interplay of dark states with interparticle interactions and opens up perspectives for optical manipulation of fermionic pairing.

18 pages, 11 figures

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