Indirect Methods to Control Population Distribution in a Large Spin System

TL;DR

This paper explores methods to manipulate population distributions in a large spin system with non-equilibrium thermodynamic properties, using non-adiabatic transitions and cavity pumping, confirmed experimentally with Gd$^{3+}$ ions.

Contribution

It introduces two novel techniques for controlling population distributions in large spin systems and demonstrates their effectiveness through experimental validation.

Findings

Successful manipulation of population distribution using Landau Zener transitions.

Effective external cavity pumping to higher energy states.

Observation of long lifetimes due to large photon transition requirements.

Abstract

We demonstrate how a large spin system ($S=7/2$) with the ground and the first excited state separated by a seven photon transition exhibit non equilibrium thermodynamic properties and how the population distribution may be manipulated using coupling between energy levels. The first method involves non-adiabatic passage through an avoided level crossing controlled with an external DC magnetic field and the resulting Landau Zener transition. The second method is based on external cavity pumping to a higher energy state hybridised with another state that is two single photon transitions away from the ground state. The results are confirmed experimentally with Gd$^{3+}$ impurity ion ensemble in a YVO$_{4}$ crystal cooled to 20 mK, which also acts as a microwave photonic whispering gallery mode resonator. Extremely long life times are observed due to large number of photons required for the transition between the ground and the first excited states.