Measuring two-body correlations via photoexcitation of ⁴⁰K₂ in an optical lattice

The properties of many-body systems with short-range interactions can be characterized by the strength of two-body correlations expressed via the contact. In atomic gases, these correlations may be probed using photoexcitation-induced trap loss of interacting atomic pairs. Here, we use a 3D optical lattice to create isolated two-body systems of fermionic ⁴⁰K and tune their interaction strength via a magnetic s-wave Feshbach resonance. In contrast to a bulk gas, the correlations of this precisely two-body system can be exactly calculated across all interaction strengths. We measure photoexcitation spectra and induced trap loss rates of these isolated Feshbach molecules and their dependence on magnetic field and lattice confinement. The measured photoexcitation loss rates are compared to those calculated using the expected short-range correlations, as well as to those of a bulk gas. These measurements of isolated two-body systems provide insight into the correlations and universal contact relations in the many-body regime.