Clock Transitions Generated by Defects in Silica Glass

TL;DR

This study reports the first ESR characterization of clock transitions in defect-rich silica glasses, revealing coherence times up to 16 microseconds and suggesting defect-related origins involving boron and aluminum vacancies.

Contribution

It provides the first experimental evidence of clock transitions in silica glasses and links these phenomena to specific defect centers involving boron and aluminum.

Findings

Clock transitions observed at zero magnetic field in borosilicate and aluminosilicate glasses.

Coherence times up to 16 microseconds at the clock transitions.

Annealing reduces or eliminates the zero-field clock transition signals.

Abstract

Clock transitions (CTs) in spin systems, which occur at avoided level crossings, enhance quantum coherence lifetimes T$_2$ because the transition becomes immune to the decohering effects of magnetic field fluctuations to first order. We present the first electron-spin resonance (ESR) characterization of CTs in certain defect-rich silica glasses, noting coherence times up to 16 $\mu$s at the CTs. We find CT behavior at zero magnetic field in borosilicate and aluminosilicate glasses, but not in a variety of silica glasses lacking boron or aluminum. Annealing reduces or eliminates the zero-field signal. Since boron and aluminum have the same valence and are acceptors when substituted for silicon, we suggest the observed CT behavior could be generated by a spin-1 boron vacancy center within the borosilicate glass, and similarly, an aluminum-vacancy center in the aluminosilicate glass.