Toward the Characterization of Atomic-Clock Transitions in the Nanomagnet [VO(TPP)]

[VO(TPP)], a promising molecular nanomagnet-based qubit candidate, has been shown to have an impressive coherence time T₂.^1,2 We employ a homebuilt electron-spin resonance (ESR) apparatus to characterize the system's behavior across a variety of frequencies in the microwave regime, using both continuous wave (cw) and pulsed ESR. By taking advantage of the CPMG pulse sequence and diluting [VO(TPP)] to 2% in a nonmagnetic structural analogue, we have shown T₂ to be greater than 8 μs at multiple frequencies. Previous work has indicated the possible presence of atomic clock transitions in [VO(TPP)] in the sub-GHz regime.¹ Strong hyperfine coupling in this S = 1/2, I = 7/2 nanomagnet generates four unique clock transitions. Decoherence from dipolar interactions and external field fluctuations is minimized at the clock transitions; as a result, T₂ has been shown to substantially increase at clock transitions in nanomagnets.³ Based on the behavior of other systems with clock transitions, we anticipate a substantially enhanced T₂ at the clock transitions in [VO(TPP)]; we present progress toward testing that expectation.

¹T. Yamabayashi, et. al., J. Am. Chem. Soc. 140, 12090-12101 (2018).

²C. Bonizzoni, et. al., npj Quantum Inf 6, 68 (2020).

³M. Shiddiq, et. al., Nature 531, 348–351 (2016).