Fig. 1: Detecting microwave magnetic fields using spins in diamond via on-chip spin-wave-mediated frequency conversion.

a Idea of the experiment. A ‘spin-wave mixer’ uses a pump to convert a microwave signal at frequency f_s to an output frequency f_NV that is detectable by nitrogen-vacancy (NV) sensor spins in diamond. b Sketch of the setup. A diamond with NV centers implanted ~10–20 nm below its surface is placed onto a film of yttrium iron garnet (YIG, thickness: 235 nm). A microstrip delivers the signal and pump microwaves, which excite spin waves in the YIG. Spin-wave mixing enables detection of the signal field by converting its frequency to the NV electron spin resonance (ESR) frequency. Inset: Atomic structure of an NV center in the diamond carbon (C) lattice. c Initialization and readout of the NV spins is achieved through excitation by a green laser and detection of the red photoluminescence (PL). The PL is stronger in the \({m}_{s}=|0\rangle\) state than in the \({m}_{s}=|\pm 1\rangle\) states. d NV spin energy levels in the electronic ground state. A magnetic field B_NV along the NV axis splits the \({m}_{s}=|\pm 1\rangle\) states via the Zeeman interaction. From the four possible configurations in the diamond lattice, we use the NV orientation with in-plane projection parallel to the stripline. f_NV denotes the \(|0\rangle \leftrightarrow|-1\rangle\) ESR transition frequency.