Precise study of asymptotic physics with subradiant ultracold molecules

TL;DR

This study precisely characterizes deeply subradiant ultracold molecules, revealing how their lifetimes are limited by radiative and nonradiative decay processes, advancing understanding of long-range interactions and precision measurement techniques.

Contribution

It provides the first detailed measurement of subradiant molecular states with extremely high quality factors, confirming quantum predictions and exploring decay mechanisms.

Findings

Subradiant states have quality factors exceeding 10^13.

Radiative decay rate increases quadratically with bond length.

Nonradiative decay via gyroscopic predissociation depends on vibrational spacing.

Abstract

Weakly bound molecules have physical properties without atomic analogues, even as the bond length approaches dissociation. In particular, the internal symmetries of homonuclear diatomic molecules result in formation of two-body superradiant and subradiant excited states. While superradiance has been demonstrated in a variety of systems, subradiance is more elusive due to the inherently weak interaction with the environment. Here we characterize the properties of deeply subradiant molecular states with intrinsic quality factors exceeding $10^{13}$ via precise optical spectroscopy with the longest molecule-light coherent interaction times to date. We find that two competing effects limit the lifetimes of the subradiant molecules, with different asymptotic behaviors. The first is radiative decay via weak magnetic-dipole and electric-quadrupole interactions. We prove that its rate increases quadratically with the bond length, confirming quantum mechanical predictions. The second is nonradiative decay through weak gyroscopic predissociation, with a rate proportional to the vibrational mode spacing and sensitive to short-range physics. This work bridges the gap between atomic and molecular metrology based on lattice-clock techniques, yielding new understanding of long-range interatomic interactions and placing ultracold molecules at the forefront of precision measurements.