Bimolecular chemistry in the ultracold regime

TL;DR

This review discusses recent progress in ultracold bimolecular chemistry, highlighting experimental techniques, control of reactions, and detailed studies of reaction dynamics at temperatures below 1 millikelvin.

Contribution

It provides a comprehensive overview of methods and experimental findings in ultracold bimolecular reactions, emphasizing new control and detection techniques at ultralow temperatures.

Findings

Observation of a long-lived reaction complex

Control of product rotational states via nuclear spins

Testing statistical models with quantum state distributions

Abstract

Advances in atomic, molecular, and optical (AMO) physics techniques allowed the cooling of simple molecules down to the ultracold regime ($\lesssim$ 1 mK), and opened the opportunities to study chemical reactions with unprecedented levels of control. This review covers recent developments in studying bimolecular chemistry at ultralow temperatures. We begin with a brief overview of methods for producing, manipulating, and detecting ultracold molecules. We then survey experimental works that exploit the controllability of ultracold molecules to probe and modify their long-range interactions. Further combining the use of physical chemistry techniques, such as mass spectrometry and ion imaging, significantly improved the detection of ultracold reactions and enabled explorations of their dynamics in the short-range. We discuss a series of studies on the reaction KRb + KRb $\rightarrow$ K$_2$ + Rb$_2$ initiated below 1 $\mu$K, including the direct observation of a long-lived complex, the demonstration of product rotational state control via conserved nuclear spins, and a test of the statistical model using the complete quantum state distribution of the products.