Crossover from the Ultracold to the Quasiclassical Regime in State-Selected Photodissociation

TL;DR

This study investigates the transition from quantum to classical behavior in molecular photodissociation, revealing how angular distributions evolve with energy and highlighting persistent quantum effects at high energies.

Contribution

It experimentally demonstrates the quantum-to-classical crossover in molecular dissociation and discusses the energy scale where this transition occurs, including quantum statistical effects.

Findings

Angular distributions depend on kinetic energy in the quantum regime.

Crossover from quantum to classical behavior occurs around 0.3 K.

Quantum statistical effects can persist at high energies.

Abstract

Processes that break molecular bonds are typically observed with molecules occupying a mixture of quantum states and successfully described with quasiclassical models, while a few studies have explored the distinctly quantum mechanical low-energy regime. Here we use photodissociation of diatomic strontium molecules to demonstrate the crossover from the ultracold, quantum regime where the photofragment angular distributions strongly depend on the kinetic energy, to the energy-independent quasiclassical regime. Using time-of-flight velocity map imaging for photodissociation channels with millikelvin reaction barriers, we explore photofragment energies in the 0.1-300 mK range experimentally and up to 3 K theoretically, and discuss the energy scale at which the crossover occurs. Furthermore, we find that the effects of quantum statistics can unexpectedly persist to high photodissociation energies.