Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 113, Issue 29, Pages 8144-8149Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1601812113
Keywords
cold atoms; mesoscopic physics; quantum simulation; superfluidity; spin transport
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Funding
- National Center of Competence in Research Quantum Science and Information Technology (NCCR QSIT)
- European Research Council (ERC) project Synthetic Quantum Many-Body Systems (SQMS)
- 7th framework (FP7) project Simulations and Interfaces with Quantum Systems (SIQS)
- Staatssekretariat fur Bildung, Forschung und Innovation (SBFI)
- Swiss National Science Foundation (NSF) under division II
- Ambizione program of the Swiss NSF
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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 1/h for weak interactions to plateau-like features at nonuniversal values as high as 4/h 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.
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