Sub-Natural-Linewidth Quantum Interference Features Observed in Photoassociation of a Thermal Gas

TL;DR

This paper reports the observation of sub-natural-linewidth quantum interference features in photoassociation of ultra-cold sodium atoms, revealing quantum effects analogous to electromagnetically induced transparency in a molecular system.

Contribution

It demonstrates for the first time that quantum interference can produce sub-natural-linewidth features in photoassociation of a thermal gas, with linewidths limited by temperature.

Findings

Observation of sub-natural-linewidth features in photoassociation

Quantum interference analogous to EIT in a molecular system

Linewidth limited by atomic temperature

Abstract

By driving photoassociation transitions we form electronically excited molecules (Na$_2^*$) from ultra-cold (50-300 $\mu$K) Na atoms. Using a second laser to drive transitions from the excited state to a level in the molecular ground state, we are able to split the photoassociation line and observe features with a width smaller than the natural linewidth of the excited molecular state. The quantum interference which gives rise to this effect is analogous to that which leads to electromagnetically induced transparency in three level atomic $\Lambda$ systems, but here one of the ground states is a pair of free atoms while the other is a bound molecule. The linewidth is limited primarily by the finite temperature of the atoms.