# Investigation of Hyperfine Interactions in Molecular Spin Qubits Constructed from A Nitronyl-Nitroxide Ligand and Transition Metal Ions

## TL;DR

This paper studies how two molecular spin qubits behave differently at various temperatures and identifies factors affecting their quantum coherence.

## Contribution

The study provides new insights into hyperfine interactions and decoherence mechanisms in molecular spin qubits.

## Key findings

- Compound 1 shows longer phase memory time at 100 K, while compound 2 outperforms at low temperatures.
- CPMG detection reveals significantly extended phase memory times at 5 K for both compounds.
- Strong spin-orbit coupling in compound 2 leads to shorter spin–lattice relaxation times compared to compound 1.

## Abstract

The qubit behavior of two S = 1/2 heterospin complexes
with the general formula (Et3NH)­[M­(hfac)2L]
has been investigated by pulse EPR methods (M = Zn (1) and Ni (2), hfac
–
is the coligand hexafluoroacetylacetonate and L
–
is the deprotonated nitrophenol-substituted NIT radical 2-(2-hydroxy-3-methoxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl). Robust quantum coherence is
observed in both compounds. At 100 K, 1 shows a longer
phase memory time, T
m (0.9 μs) than 2 (0.12 μs), while at very low temperatures, the opposite
is true (1: 1.78 μs at 5.2 K; 2: 3.7
μs at 5.5 K). With CPMG detection, longer T
m up to18 μs (1) and 7 μs (2) at 5 K is measured. The spin–lattice relaxation
time (T
1) is also longer for 1 than for 2, due to strong spin-orbit coupling in the
latter. HYSCORE and ENDOR investigations quantified the hyperfine
couplings to 19F, 1H, 67Zn, and 14N, providing clear insights into the low temperature decoherence
paths in the two qubits.