High-resolution spectroscopy of single nuclear spins via sequential weak measurements

TL;DR

This paper demonstrates high-resolution NMR of a single nuclear spin at room temperature using sequential weak measurements, overcoming quantum back-action to achieve 3.8 Hz spectral resolution.

Contribution

It introduces a novel sequential weak measurement technique for single nuclear spins, enabling high spectral resolution without sensitivity loss.

Findings

Achieved 3.8 Hz spectral resolution in single-spin NMR

Observed a quantum phase transition due to measurement back-action

Enabled detection of weakly coupled single spins

Abstract

Quantum sensors have recently achieved to detect the magnetic moment of few or single nuclear spins and measure their magnetic resonance (NMR) signal. However, the spectral resolution, a key feature of NMR, has been limited by relaxation of the sensor to a few kHz at room temperature. The spectral resolution of NMR signals from single nuclear spins can be improved by, e.g., using quantum memories, however at the expense of sensitivity. Classical signals on the other hand can be measured with exceptional spectral resolution by using continuous measurement techniques, without compromising sensitivity. To apply these techniques to single-spin NMR, it is critical to overcome the impact of back action inherent of quantum measurements. Here we report sequential weak measurements on a single $^{13}$C nuclear spin. The back-action of repetitive weak measurements causes the spin to undergo a quantum dynamics phase transition from coherent trapping to coherent oscillation. Single-spin NMR at room-temperature with a spectral resolution of 3.8 Hz is achieved. These results enable the use of measurement-correlation schemes for the detection of very weakly coupled single spins.