Quadrupolar resonance spectroscopy of individual nuclei using a room-temperature quantum sensor

TL;DR

This paper demonstrates room-temperature quadrupolar resonance spectroscopy of individual nuclei using NV centers in diamond, enabling detailed study of single-molecule nuclear environments and new Hamiltonian insights.

Contribution

The work introduces a method for performing NQR spectroscopy on individual nuclei at room temperature using NV centers, revealing minute variations and symmetry-breaking effects.

Findings

Resolved variations between individual $^{14}$N nuclei.

Discovered a previously unreported Hamiltonian term.

Established control sequences for nuclear quantum states.

Abstract

Nuclear quadrupolar resonance (NQR) spectroscopy reveals chemical bonding patterns in materials and molecules through the unique coupling between nuclear spins and local fields. However, traditional NQR techniques require macroscopic ensembles of nuclei to yield a detectable signal, which precludes the study of individual molecules and obscures molecule-to-molecule variations due to local perturbations or deformations. Optically active electronic spin qubits, such as the nitrogen-vacancy (NV) center in diamond, facilitate the detection and control of individual nuclei through their local magnetic couplings. Here, we use NV centers to perform NQR spectroscopy on their associated nitrogen-14 ($^{14}$N) nuclei at room temperature. In mapping the nuclear quadrupolar Hamiltonian, we resolve minute variations between individual nuclei. The measurements further reveal correlations between the parameters in the NV center's electronic spin Hamiltonian and the $^{14}$N quadropolar Hamiltonian, as well as a previously unreported Hamiltonian term that results from symmetry breaking. We further design pulse sequences to initialize, readout, and control the quantum evolution of the $^{14}$N nuclear state using the nuclear quadrupolar Hamiltonian.