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A tiny defect in a diamond crystal works like a sensitive antenna. When a magnetic field oscillates nearby, this defect, a nitrogen vacancy, responds by glowing. Previously, to hear the signal, you had to accumulate many repeated measurements, like listening to a whisper with your ear pressed against a door. Now a single short "look" suffices.

The authors showed that the strength and phase of an alternating magnetic field at a frequency of 4 megahertz can be extracted from just two consecutive measurements. The accuracy is 78 nanoteslas in amplitude and 63 milliradians in phase, with a temporal resolution of 320 microseconds. For comparison, 78 nanoteslas is roughly one hundred thousand times weaker than Earth's magnetic field.

The scientists also tested what happens when the probe frequency does not match the field frequency and how the method behaves in strong fields. Errors can be estimated in advance. Moreover, the protocol allows changing the probe frequency during the experiment, like tuning a radio on the fly.

This approach brings diamond sensors closer to observing fast magnetic processes in real time: from neuron firing to vortices in superconductors. One diamond, one measurement, and an instant snapshot of the invisible.

Original abstract

as written by the authors arXiv:2602.23712

Nitrogen-vacancy centers in diamond have been shown to be capable of detecting AC magnetic fields with high sensitivity, spectral resolution, and spatial resolution. However, most studies so far have focused on the regime of time-averaged or time-correlated measurements, while little attention has been paid to the single-shot regime. Here we show that the amplitude and phase of an AC field can be retrieved from a single pair of two consecutive measurements. We demonstrate this concept by measuring a 4 MHz AC field with a per-shot amplitude and phase sensitivity of 78 nT and 63 mrad, respectively, at a temporal resolution of 320 us. We also investigate the effects and quantify the errors resulting from probe frequency detunings, as well as operating in the strong field regime. Moreover, we showcase the ability of the measurement protocol to dynamically change the probe frequency in real-time. This work advances the use of NV centers for real-time measurements of AC magnetic fields.