Multidimensional spectroscopy of heavy impurities in ultracold fermions

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.

Automated summary

We investigated a system where a heavy impurity is immersed in a degenerate Fermi gas and its internal degree of freedom is manipulated by a series of radio-frequency pulses. Using the functional determinant approach, we calculated the precise Ramsey-interference-type responses to these pulses, which can be regarded as multidimensional spectroscopy of the system in the time domain. Fourier transforming the time intervals gave the multidimensional spectroscopy in the frequency domain, providing valuable insights into many-body correlation and relaxation.