A directly observable, Zeeman-insensitive nuclear spin coherence in solution

TL;DR

This paper demonstrates a long-lived, directly observable nuclear spin coherence in solution at ultralow magnetic fields, immune to magnetic perturbations, with potential applications in quantum sensing and molecular spectroscopy.

Contribution

It introduces a novel clock-like nuclear spin transition in a molecular liquid that is insensitive to magnetic field fluctuations and exhibits extended coherence times.

Findings

Achieved a 25 s coherence lifetime in a nuclear spin transition.

Demonstrated immunity of the transition to magnetic field perturbations.

Observed sensitivity to internal dipolar fields within the sample.

Abstract

Clock transitions are well known in atomic and solid-state systems, but are largely unexplored in molecular liquids. Here we demonstrate a clock-like, nuclear-spin avoided crossing in [1--$^{13}$C]-fumarate that supports long-lived and directly observable coherences at ultralow magnetic field: a three-spin transition $|S_0\alpha\rangle \leftrightarrow |T_{+1}\beta\rangle$ near 400 nT exhibits a shallow crossing with a frequency minimum of 2 Hz. The transition is first-order immune to magnetic field perturbations and displays a lifetime of 25 s, around three times the longest single-spin $T_2^*$. Sensitivity to effective pseudo-fields is also demonstrated, including the internal dipolar field of the sample.