npj Quant. Info. 3, 28 (2017)

Nitrogen–vacancy (NV) defects in diamond are quantum mechanical systems characterized by long coherence times at room temperature — an advantageous property in view of the potential use of these colour centres as spin qubits. Several proposals have been put forward for hybrid devices allowing the remote control of the defects' quantum state mediated by phonons or magnons. However, a common drawback of coupling NV centres with the environment is the strong suppression of their characteristic coherence times. This is particularly the case for the magnetic coupling with spin waves — often dominated by incoherent mechanisms.

Now, Andrich et al. demonstrate the long-distance coherent control of NV centres by exploiting spin-wave modes. The researchers fabricate a magnonic device based on an yttrium iron garnet magnetic thin film where surface spin-waves propagate after injection by a microstrip microwave antenna. Nanodiamonds containing NV centres are also deposited on the yttrium iron garnet surface, and the evolution of the quantum state of the defects — resonantly coupled to spin-waves under the combined effect of an external magnetic field — is monitored by measuring their photoluminescence. At low-power conditions for the spin-wave injection, the researchers induce and detect Rabi oscillations in NV centres at distances of ∼100 μm from the microstrip antenna. Further coherent control of the defects' quantum state is demonstrated by exploiting multi-pulse dynamical decoupling protocols.