Probing Interactions between Ultracold Fermions

TL;DR

This paper investigates density-dependent collisional frequency shifts in ultracold fermionic Sr atoms used in optical clocks, revealing inhomogeneity-induced distinguishability and providing insights for reducing clock errors.

Contribution

It presents the first systematic measurement and theoretical analysis of collisional shifts in ultracold fermionic optical lattice clocks.

Findings

Density-dependent frequency shifts observed in fermionic Sr atoms.

Inhomogeneities in probe excitation cause atoms to become distinguishable.

Insights for minimizing density shifts in optical clock applications.

Abstract

At ultracold temperatures, the Pauli exclusion principle suppresses collisions between identical fermions. This has motivated the development of atomic clocks using fermionic isotopes. However, by probing an optical clock transition with thousands of lattice-confined, ultracold fermionic Sr atoms, we have observed density-dependent collisional frequency shifts. These collision effects have been measured systematically and are supported by a theoretical description attributing them to inhomogeneities in the probe excitation process that render the atoms distinguishable. This work has also yielded insights for zeroing the clock density shift.