title: Mapping out spin and particle conductances in a quantum point contact.
abstract: We study particle and spin transport in a single-mode quantum point contact, using a charge neutral, quantum degenerate Fermi gas with tunable, attractive interactions. This yields the spin and particle conductance of the point contact as a function of chemical potential or confinement. The measurements cover a regime from weak attraction, where quantized conductance is observed, to the resonantly interacting superfluid. Spin conductance exhibits a broad maximum when varying the chemical potential at moderate interactions, which signals the emergence of Cooper pairing. In contrast, the particle conductance is unexpectedly enhanced even before the gas is expected to turn into a superfluid, continuously rising from the plateau at [Formula: see text] for weak interactions to plateau-like features at nonuniversal values as high as [Formula: see text] for intermediate interactions. For strong interactions, the particle conductance plateaus disappear and the spin conductance gets suppressed, confirming the spin-insulating character of a superfluid. Our observations document the breakdown of universal conductance quantization as many-body correlations appear. The observed anomalous quantization challenges a Fermi liquid description of the normal phase, shedding new light on the nature of the strongly attractive Fermi gas.
authors.affiliation: Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Krinner
authors.affiliation: Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Lebrat
authors.affiliation: Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: Dominik
authors.initials: D
authors.lastname: Husmann
authors.affiliation: Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: Charles
authors.initials: C
authors.lastname: Grenier
authors.affiliation: Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland brantutj@phys.ethz.ch.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Brantut
authors.affiliation: Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: Tilman
authors.initials: T
authors.lastname: Esslinger
keywords: cold atoms; mesoscopic physics; quantum simulation; spin transport; superfluidity