Quantum Whisper in Diamond ⚡ экспресс
Spin ensembles form the backbone of quantum frequency standards, magnetic spectroscopy, and sensors. Their precision is bounded by spin projection noise, but in solid-state implementations, photon shot noise has dominated—until now. We demonstrate a direct quantum non-demolition readout method for a mesoscopic NV-center ensemble in diamond that breaks the photon shot noise limit and approaches the intrinsic projection noise. Stabilizing 14N nuclear spins with a strong magnetic field and using multiple nuclear-assisted readout cycles lowered the noise by 3.8 dB below the thermal projection noise floor. This granted direct access to the ensemble’s native fluctuations and revealed signatures of correlated spin states. The result establishes projection-noise-level readout as a practical technique for solid-state quantum sensors and opens avenues for quantum-enhanced metrology, direct observation of many-body correlations, and generation of squeezed spin states in mesoscopic solid-state ensembles.
Every elementary particle has its own rotation—spin. These tiny magnetic spinning tops constantly tremble, generating a faint noise. Hearing it is hindered by the din of light used in detectors. But in a diamond with artificial defects—glowing NV centers—scientists found a loophole. Nitrogen atoms near the defects act like stable 'recorders': their nuclei record the trembling of electron spins, ignoring the optical cacophony.
Repeated readout using spectroscopy allowed the useful whisper to accumulate and reduced overall noise by 3.8 decibels—approaching the fundamental quantum limit. For the first time, correlations between spins appeared without distortion: how they 'talk' to each other. This opens the era of quantum sensors with unprecedented sensitivity. For example, such defects are already able to detect the magnetic field of a single protein molecule—and operate inside a living cell. In perspective—squeezing of spin states for even more precise measurements.
🎯 NV centers can detect the magnetic field of a single protein molecule—they are being explored as nanosensors inside living cells.