Quantum Simulation of an FFLO Superconductor

William Marsh Rice University, Houston TX

Investigators

Abstract

The discovery of superconductivity was a watershed moment in 20th century physics, sparking the new field of condensed matter physics, as well as enabling new technologies. The essence of superconductivity is that some materials become perfect conductors of electricity when cooled below a critical temperature Tc. Tc is typically below the temperature where air liquifies. The mechanisms that underlie superconductivity are not fully known, nor do we know the upper limit of Tc. We do know that the charge-carrying particles are pairs of electrons that are weakly bound to each other by various effective interactions. One of the proposed pairing mechanisms is the “FFLO superconductor,” named after the initials of the four proposers, in which the pairs may survive the presence of a strong magnetic field. Despite many searches, the FFLO superconductor remains elusive. Its existence, however, would give physicists more insight into the inner workings of superconductivity and it would unlock new applications, such as ultra-fast electronic computers and magnetic resonance imaging (MRI). The PI will use quantum simulation to realize a model of the FFLO superconductor, for which ultra-cold atoms stand-in for the electrons, which move in a periodic crystal lattice made from standing waves of light. This type of quantum simulation faithfully realizes a model of the FFLO superconductor and will enable the PI and students to test the theoretical predictions. Several students are expected to earn PhD degrees working on this project with the PI, and likely some of these will gain employment at innovative start-up companies contributing their expertise to develop new technologies for quantum computation. Superconductivity and magnetism are phases of matter commonly found in electronic materials that do not coexist. The FFLO superconductor may adapt to a co-existing magnetic field if the Cooper pairs acquire a finite center-of-mass momentum rather than forming zero momentum pairs as in the standard theory of superconductivity. It is believed that FFLO is most favored in low-dimensions, either in quasi-1D or 2D. As of yet, there is no direct evidence for finite momentum Cooper pairs. The PI will resolve whether the FFLO state, with finite-momentum pairing, is a legitimate phase of matter by simulating the actual electronic materials subjected to a magnetic field, with a spin-imbalanced atomic Fermi gas confined to a two-dimensional array of one-dimensional waveguides formed using a 2D optical lattice. The lattice potential is weak enough that atoms in adjacent waveguides interact via tunnel coupling. The resulting domain walls, the definitive signature of the FFLO state, will be directly imaged. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.