Cooperative Spin Amplifier for Enhanced Quantum Sensing

Quantum sensing is crucial for precision measurements, yet quantum sensor sensitivity is often limited by the coherence time of the quantum system. Here, we demonstrate a method to enhance coherence time through cooperative spins. Using a tunable feedback circuit, we induce cooperation among noble-gas ^{129}Xe spins, resulting in an impressive 18-fold coherence enhancement. Moreover, we show that the cooperative ^{129}Xe spins can significantly amplify magnetic signals by at least 3 orders of magnitude. Magnetic field sensing assisted with such a cooperative spin amplifier realizes the sensitivity of 4 fT/Hz^{1/2} and surpasses the spin-projection noise of the embedded ^{87}Rb spin gas magnetometer. These results pave the way for a new class of "cooperative quantum sensors," and open up exciting prospects in fundamental physics.