Quantum Sensing of Magnetic Fields

Quantum entanglement can improve the sensitivity of a measurement, as has been demonstrated previously for atomic clocks and magnetic-field sensors. A new experiment with a cloud of cold atoms is able to measure a weak magnetic-field signal with a 25% reduction in experimental noise, thanks to entanglement of the atoms. The method involves a sequence of quantum nondemolition (QND) measurements, which track the effect of the magnetic signal on the atoms’ spins without destroying their quantum coherence. The advantage of this technique is that it can measure arbitrary field waveforms (sine wave, chirp, etc.), which might allow it to pinpoint the magnetic signal coming from the firing of a single neuron.