An optically pumped diamond maser continued emitting microwaves for 40 to 50 microseconds after its pump was switched off, across three operating regimes, according to an arXiv preprint. The study reports long-lived coherence involving about 10^14 NV− spins and about 10^9 microwave-cavity photons under ambient conditions.
The residual signal lasted longer than the cavity-leakage and spin-dephasing times but shorter than the spin-relaxation time. The authors interpret that persistence as evidence that macroscopic quantum coherence can be generated and maintained in the solid.
Three regimes from one setup
The platform was an isotopically purified diamond containing an ensemble of NV− centers coupled to a TE01δ mode of a microwave cavity. The cavity resonated at 9.360 gigahertz. The effective number of optically pumped and cavity-coupled centers was estimated at (1.40 ± 0.05) × 10^14, so the population figure is an estimate rather than a direct count.
Researchers recorded signals in both time and frequency domains while varying the magnetic field, pump rate and cavity quality factor. These sweeps produced phase diagrams showing how the maser behaved as the settings changed.
To represent inhomogeneous broadening, the numerical analysis grouped the ensemble into 321 spin sub-ensembles. The mean-field simulations reproduced the main experimental features with reasonable quantitative agreement.
The resulting map contained three reported regimes: continuous-wave, or CW, masing; PAM masing, interpreted as a coherent time crystal; and superradiant bursts with random relative phases and intervals.
From a sharp line to irregular bursts
In the continuous-wave regime, a representative maser spectrum showed a single sharp peak. Its full width at half maximum, or FWHM, was 164 hertz, and the reported coherence time was 1.94 milliseconds.
Those figures describe one representative measurement, not an uncertainty range across repeated measurements.
At an optical pump power of 1.7 watts, the maximum reported CW output was approximately −52.3 dBm, corresponding to about 1.45 × 10^9 photons inside the cavity.
Across phase-diagram measurements, intracavity power reached a maximum of 12 nanowatts. The study used W/Wth as a normalized pump rate; W/Wth = 1 corresponded to a pump power of 33 milliwatts.
The burst regime had a distinct signature: intervals between bursts and their peak amplitudes were random or fluctuating. The analysis included 29 successive experimental bursts from nine runs and 266 successive simulated bursts.
The bursts were therefore interpreted as having random relative phases rather than a shared phase relation, in contrast with the coherent interpretation assigned to PAM masing. That phase interpretation relies partly on simulations, whose main experimental features were reproduced with reasonable quantitative agreement.
A result with a narrow scope
The experiment used one diamond sample, and no independent sample replication was reported. The numerical treatment used a mean-field approximation—an averaged description of the ensemble—and finite spin sub-ensembles.
The study does not fully characterize many-body quantum correlations in the emitted microwave field, squeezing or quantum advantage. It also does not demonstrate the proposed sensing, communication or spectroscopy applications.
Whether the phase diagram and coherence scales can be reproduced across samples and apparatuses remains open, as does the question of how engineered spin-frequency distributions and interactions would affect higher-order correlations.
The report gives no formal uncertainty for the regime boundaries, and the CW linewidth is identified as a representative measurement without replicate-level uncertainty.
Preprint status and disclosures
The document is an arXiv preprint identified as arXiv:2608.23748v1 and dated 24 August 2026.
The work was supported by the New Cornerstone Science Foundation, CRS-CUHK401/22 and SRFS2223-4S01. The authors declared no conflict of interest or competing interests.
Paper data and sources
Original title: Sustained macroscopic quantum coherence in a superradiant solid under ambient conditions
Authors: Wei-Jiang Wu, Da-Wu Xiao, Wen-Tao Wang et al.
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-24
DOI: Not available
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