A quantum spectrum analyzer enhanced by a nuclear spin memory

TL;DR

This paper demonstrates a quantum spectrum analyzer using a nitrogen-vacancy center in diamond with a nuclear spin memory, achieving significantly improved spectral resolution for external signals and NMR by leveraging long-lived quantum states.

Contribution

The authors develop a two-qubit quantum sensor with a nuclear spin memory, enabling high spectral resolution in quantum sensing experiments, a novel approach in quantum spectroscopy.

Findings

Achieved 45 ms state storage time in the quantum sensor.

Demonstrated 19 Hz spectral line width for external signals.

Achieved 190 Hz line width for NMR signals, 100 times better than without nuclear memory.

Abstract

We realize a two-qubit sensor designed for achieving high spectral resolution in quantum sensing experiments. Our sensor consists of an active "sensing qubit" and a long-lived "memory qubit", implemented by the electronic and the nitrogen-15 nuclear spins of a nitrogen-vacancy center in diamond, respectively. Using state storage times of up to 45 ms, we demonstrate spectroscopy of external ac signals with a line width of 19 Hz (~2.9 ppm) and of carbon-13 nuclear magnetic resonance (NMR) signals with a line width of 190 Hz (~ 74 ppm). This represents an up to 100-fold improvement in spectral resolution compared to measurements without nuclear memory.