Modulation Spectroscopy of the Attractive Fermi-Hubbard Model*

The attractive Fermi-Hubbard model provides a simple model for exploring pairing in quantum many-body systems of fermions. In previous works [1], we experimentally established the existence of a pseudo-gap regime, in which the system had full spin pairing at a temperature above the onset of superfluidity. We probe the response of such states to modulation of the interaction strength. Calculation of dynamic responses is particularly challenging for classical simulations, making quantum simulation especially appealing for this measurement. By measuring the spectrum of the modulation response, we determine the pair binding energy across a decade of interaction strengths. Our range of measurements further enables us to ascertain the local fraction of pairs. Finally, by comparing the response of the interaction energy and kinetic energy of the system, we gain insight into how paired and unpaired fermions exchange energy in this system.

[1] T. Hartke et al. Direct observation of nonlocal fermion pairing in an attractive Fermi-Hubbard gas. In: Science 381.6653 (2023), pp. 82–86.