Influence of non-equilibrium phonons on the spin dynamics of a single Cr atom

TL;DR

This study investigates how optically generated non-equilibrium phonons influence the spin relaxation and temperature of a single Cr atom in a quantum dot, revealing tunable spin-lattice interactions and conditions for efficient spin state manipulation.

Contribution

It demonstrates the impact of non-equilibrium phonons on Cr atom spin dynamics and introduces a tunable spin-lattice coupling mechanism based on phonon density.

Findings

Spin relaxation depends on optical excitation conditions.

Heating occurs within hundreds of nanoseconds after excitation.

Cooling times exceed tens of microseconds, independent of excitation.

Abstract

We analyse the influence of optically generated non-equilibrium phonons on the spin relaxation and effective spin temperature of an individual Cr atom inserted in a quantum dot. Using a three pulses pump-probe technique, we show that the spin relaxation measured in resonant optical pumping experiments strongly depends on the optical excitation conditions. We observe for an isolated Cr in the dark a heating time shorter than a few hundreds $ns$ after an initial high power non-resonant excitation pulse. A cooling time larger than a few tens of $\mu s$, independent on the excitation, is obtained in the same experimental conditions. We show that a tunable spin-lattice coupling dependent on the density of non-equilibrium phonons can explain the observed dynamics. Low energy excitation conditions are found where the Cr spin states S$_z$=$\pm$1 can be efficiently populated by a non-resonant optical excitation, prepared and read-out by resonant optical pumping and conserved in the dark during a few $\mu$s.