Free coherent evolution of a coupled atomic spin system initialized by electron scattering

TL;DR

This study demonstrates real-time tracking of coupled atomic spins' coherent evolution using scanning tunneling microscopy, revealing conditions for entanglement and controlled quantum state migration.

Contribution

It introduces a pump-probe STM method to observe and control the coherent dynamics of coupled atomic spins at the single-spin level.

Findings

Matching Larmor frequencies enable spin entanglement.

Local electron-spin scattering affects spin dynamics.

Controlled quantum state migration is possible in spin lattices.

Abstract

Full insight into the dynamics of a coupled quantum system depends on the ability to follow the effect of a local excitation in real-time. Here, we trace the coherent evolution of a pair of coupled atomic spins by means of scanning tunneling microscopy. We use a pump-probe scheme to detect the local magnetization following a current-induced excitation performed on one of the spins. Making use of magnetic interaction with the probe tip, we are able to tune the relative precession of the spins. We show that only if their Larmor frequencies match, the two spins can entangle, causing the excitation to be swapped back and forth. These results provide insight into the locality of electron-spin scattering, and set the stage for controlled migration of a quantum state through an extended spin lattice.