Phase-locking between different partial-waves in atom-ion spin-exchange collisions

TL;DR

This study investigates spin dynamics in atom-ion collisions, revealing that phase-locking between partial waves influences spin-exchange and relaxation rates, with quantum interference effects observed across multiple partial waves.

Contribution

It provides the first combined experimental and theoretical analysis showing phase-locking of singlet-triplet phase differences across partial waves affecting spin-exchange.

Findings

Spin-exchange occurs after approximately 9 Langevin collisions.

Spin-relaxation of Sr+ ion occurs after about 48 Langevin collisions, slower than in other systems.

The singlet-triplet phase difference remains constant over many partial waves, leading to quantum interference.

Abstract

We present a joint experimental and theoretical study of spin dynamics of a single $^{88}$Sr$^+$ ion colliding with an ultracold cloud of Rb atoms in various hyperfine states. While spin-exchange between the two species occurs after 9.1(6) Langevin collisions on average, spin-relaxation of the Sr$^+$ ion Zeeman qubit occurs after 48(7) Langevin collisions which is significantly slower than in previously studied systems due to a small second-order spin-orbit coupling. Furthermore, a reduction of the endothermic spin-exchange rate was observed as the magnetic field was increased. Interestingly, we found that, while the phases acquired when colliding on the spin singlet and triplet potentials vary largely between different partial waves, the singlet-triplet phase difference, which determines the spin-exchange cross-section, remains locked to a single value over a wide range of partial-waves which leads to quantum interference effects.