Multidimensional spectroscopy of heavy impurities in ultracold fermions

Abstract

We investigate the system of a heavy impurity immersed in a degenerate Fermi gas, where the impurity's internal degree of freedom (pseudospin) is manipulated by a series of radio-frequency (RF) pulses at several different times. Applying the functional determinant approach, we carry out an essentially exact calculation of the Ramsey-interference-type responses to the RF pulses. These responses can be regarded as multidimensional (MD) spectroscopy of the system in the time domain. Similar to their one-dimensional counterpart studied by Knap et al. [M. Knap et al., Phys. Rev. X 2, 041020 (2012)], these responses are universal functions. A Fourier transformation of the time intervals gives the MD spectroscopy in the frequency domain, providing insightful information on the many-body correlation and relaxation via the cross peaks, e.g., the off-diagonal peaks in a two-dimensional spectrum. These features are inaccessible for the conventional, one-dimensional absorption spectrum. Our scheme provides a different method to investigate many-body nonequilibrium physics beyond the linear response regime with accessible tools in cold atoms.