Detecting chiral pairing and topological superfluidity using circular dichroism

Realizing and probing topological superfluids is a key goal for fundamental science, with exciting technological promises. Here, we show that chiral px+ipy pairing in a two-dimensional topological superfluid can be detected through circular dichroism, namely, as a difference in the excitation rates induced by a clockwise and counterclockwise circular drive. For weak pairing, this difference is to a very good approximation determined by the Chern number of the superfluid, whereas there is a nontopological contribution scaling as the superfluid gap squared that becomes significant for stronger pairing. This gives rise to a competition between the experimentally driven goal to maximize the critical temperature of the superfluid, and observing a signal given by the underlying topology. Using a combination of strong-coupling Eliashberg and Berezinskii-Kosterlitz-Thouless theory, we analyze this tension for an atomic Bose-Fermi gas, which represents a promising platform for realizing a chiral superfluid. We identify a wide range of system parameters where both the critical temperature is high and the topological contribution to the dichroic signal is dominant.