Coherence Enhancement via Clock Transitions Generated by Defects in Silica Glasses*

Nanomagnetic systems that exhibit clock transitions (CTs) have potential to serve as good qubits due to their ability to suppress the decohering effects of magnetic fluctuations to first order, resulting in enhanced coherence times T₂ [1,2]. Silica (SiO₂)-based glasses containing certain defects exhibit similar zero-field CT effects. In particular, borosilicate glass has coherence times up to 5 μs at its CT, with further enhancement of the coherence via the CPMG pulse sequence up to 25 μs. We present characterization of these CTs using electron-spin resonance spectroscopy techniques in S band in several different silica glass samples, including borosilicate and aluminosilicate glasses, and complement this investigation with DC magnetization studies that helps reveal the spin physics of these systems. The materials origin of these CTs is investigated via comparison to related materials, including boron and aluminum oxides, fused silica, and glasses with only interstitial defects in the material matrix. Since boron and aluminum are acceptors when substituted for silicon, we suggest that the observed CT behavior is due to a spin-1 boron-vacancy center within the borosilicate glass, and similarly, an aluminum-vacancy center in the aluminosilicate glass.

¹M. Shiddiq, et al., Nature 531, 348–351 (2016).

²C. Collett, et al., Magnetochemistry 5, 1 (2019).