Stochastic quantization and spin-polarized Fermi gases

Abstract

Experiments with ultracold fermionic gases are thriving and continue to provide us with valuable insights into fundamental aspects of physics. A special system of interest is the so-called unitary Fermi gas (UFG) situated right in the "middle" of the crossover between Bardeen-Cooper-Schrieffer superfluidity and Bose-Einstein condensation. However, the theoretical treatment of these gases is highly challenging due to the absence of a small expansion parameter as well as the appearance of the infamous sign problem in the presence of, e.g., finite spin polarizations. In this talk, I will discuss the concept of stochastic quantization and motivate the complex Langevin (CL) method for non-relativistic fermions as an alternative to conventional Monte Carlo approaches. In particular, I will show how the CL approach can be employed to study the spin-polarized UFG. In the unpolarized limit, our results for the EOS are in excellent agreement with the existing state-of-the-art results from other ab-initio approaches as well as with experimental data. For the polarized case, our results for the EOS and other thermodynamic quantities represent experimentally testable predictions, already providing us with some insight into the underlying phase diagram.