Coherence Time Enhancement in the [VO(TPP)] Molecular Nanomagnet*

The metal-organic [VO(TPP)] molecular nanomagnet has shown promise as a quantum memory qubit due to its impressive coherence time T₂.¹ Here, we investigate its behavior in the microwave regime with continuous wave (cw) and pulsed electron-spin resonance (ESR) techniques, using a homebuilt ESR spectrometer. We report progress on mapping ESR transitions in cw across varying frequency and field, with the ultimate goal of identifying an atomic-clock transition² in the sub-GHz regime. Eight ESR transitions can clearly be seen due to hyperfine coupling in this S = 1/2, I = 7/2 system. Pulsed ESR experiments show long T₂ times at several frequencies in excess of 8 μs through usage of the CPMG pulse sequence, suggesting improvement over previous work. Diluted samples of 2% [VO(TPP)] allow for a reduction in dipolar interactions and therefore a further enhancement of the coherence time. Finally, we discuss progress towards measuring T₂ at the clock transitions, where decoherence from dipole and hyperfine interactions is expected to be minimized.

¹T. Yamabayashi, et. al., J. Am. Chem. Soc. 140, 12090-12101 (2018).
²M. Shiddiq, et. al., Nature 531, 348–351 (2016).