A Clock Transition in Borosilicate Glass*

Clock transitions in molecular nanomagnets have strong potential for use as qubits because of their unique property of shielding spin qubits from local magnetic fluctuations to first order. Clock transitions in nanomagnets have been shown to substantially enhance coherences times (T₂)^1,2 by protecting the nanomagnets from spin-bath decoherence. Borosilicate glass, a common form of SiO₂ glass enriched with B₂O₃, shows particular promise as a clock transition-based qubit, with coherence times up to 5 μs at the clock transition. By employing the CPMG pulse sequence, the coherence time can be extended up to 25 μs at the clock transition. Using our homebuilt electron spin resonance (ESR) spectrometer, we characterize the clock transition in borosilicate glass and other chemically and stoichiometrically similar materials, including Corning Vycor glass (a borosilicate glass with a lower concentration of B₂O₃), while ruling out the presence of a clock transition in pure B₂O₃ and in fused silica. A comparison of the spin dynamics of these materials provides insight into the physics underlying the observed clock transition.

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

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

*Work supported by RCSA Cottrell SEED Award #27849.