The Hubbard model of attractively interacting fermions provides a paradigmatic setting for fermion pairing, featuring a crossover between Bose-Einstein condensation (BEC) of tightly bound pairs and Bardeen-Cooper-Schrieffer (BCS) superfluidity of long-range Cooper pairs, and a “pseudo-gap” region where pairs form already above the superfluid critical temperature. Pairing of fermions lies at the heart of superconductivity, the hierarchy of nuclear binding energies and superfluidity of neutron stars. Direct observation of non-local fermion pairing in an attractive Fermi-Hubbard gas ().Our goal is to use these gases as model systems for strongly interacting quantum matter, from High-T c superconductors to Neutron Stars. In contrast to bulk materials, we can freely tune the interaction between atoms and, for example, explore the crossover from a Bose-Einstein condensate of tightly bound molecules to a Bardeen-Cooper-Schrieffer superfluid of long-range fermion pairs. This is directly related to superconductivity in metals, where electron pairs transport current without resistance.
In ultracold Fermi gases, atoms team up in pairs that can flow without friction. At temperatures a million times colder than interstellar space, and at densities a million times thinner than air, quantum mechanics takes center stage: Atoms behave as waves, they interfere like laser light, and form novel states of matter, such as Bose-Einstein condensates and fermionic superfluids. Our group studies ultracold gases near Absolute Zero temperature.
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