Photoassociation of spin polarized Chromium

TL;DR

This study reports the first homonuclear photoassociation of ultracold chromium atoms, revealing a surprisingly simple spectrum and providing detailed measurements of interaction potentials, with implications for understanding complex atomic interactions.

Contribution

It presents the first measurement of photoassociation in an element with total electron spin greater than 1, and characterizes the interaction potentials in ultracold chromium.

Findings

Observed two vibrational series following LeRoy-Bernstein law

Determined C3 coefficients for relativistic adiabatic potentials

Identified potential energy curves using theoretical calculations

Abstract

We report the homonuclear photoassociation (PA) of ultracold ${}^{52}\mathrm{Cr}$ atoms in an optical dipole trap. This constitutes the first measurement of PA in an element with total electron spin $\tilde{S}>1$. Although Cr, with its ${}^{7}\mathrm{S}_{3}$ ground and ${}^{7}\mathrm{P}_{4,3,2}$ excited states, is expected to have a complicated PA spectrum we show that a spin polarized cloud exhibits a remarkably simple PA spectrum when circularly polarized light is applied. Over a scan range of 20 GHz below the ${}^{7}\mathrm{P}_{3}$ asymptote we observe two distinct vibrational series each following a LeRoy-Bernstein law for a $C_3 / R^{3}$ potential with excellent agreement. We determine the $C_3$ coefficients of the Hund's case c) relativistic adiabatic potentials to be -1.83$\pm$0.02 a.u. and -1.46$\pm$0.01a.u.. Theoretical non-rotating Movre-Pichler calculations enable a first assignment of the series to $\Omega=6_u$ and $5_g$ potential energy curves. In a different set of experiments we disturb the selection rules by a transverse magnetic field which leads to additional PA series.