Sensing and control of interacting electron-spin pairs in diamond

Optically accessible spin defects have emerged as a promising platform for quantum sensing and quantum information. The canonical system formed by a central defect spin and the surrounding bath of other spins has been widely used to study the decoherence of spin qubits and as a test bed for quantum sensing. An electron spin in a nuclear spin bath imprints a strong coherent back action on the bath spins, which has been used to sense, image and control the nuclear spins, including for applications as qubits in quantum networks and computation. However, for an electron-spin bath, back action has been traditionally considered negligible, so that the bath forms a classical source of noise. In this work, we demonstrate a strong coherent back action of a central NV center electron spin on the dynamics of a pair of coupled electron spins in a bath of P1 centers in diamond. The key to this observation is that we access microscopic single-spin configurations in a time resolved way, rather than ensemble averaging. We then use this coherent interaction to demonstrate complete control over the spin-pair qubit, to reveal very long dephasing times (T₂^*= 44(9) ms), and to image the NV-P1-P1 system with atomic scale resolution. These results provide new opportunities for the control of spin qubits and for the quantum sensing of interacting electron spin systems.