Toward the Understanding of a Zero-Field Clock Transition in Borosilicate Glass

Clock transitions (CTs) in molecular nanomagnets have potential for use as qubits because the decohering effects of magnetic fluctuations are suppressed to first order, leading to enhanced coherences times T₂ [1,2]. While not a molecular nanomagnet, borosilicate glass, a structural SiO₂-based glass enriched with B₂O₃, shows promise as a CT-based qubit with coherence times up to 5 μs at the clock transition. By employing the CPMG pulse sequence, T₂ can be extended up to 25 μs at the clock transition. Using electron spin resonance techniques, we characterize the CT in borosilicate glass and similar materials, including borosilicate glass with different concentrations of B₂O₃, while ruling out the presence of a CT in pure B₂O_3, quartz (crystalline SiO₂), and soda-lime glass. A comparison of the spin dynamics of these materials provides insight into the physics underlying the observed clock transition. We hypothesize that the CT is due to spin-1 boron vacancy centers within the borosilicate glass.

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

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