A Four-Channel BiCMOS Transmitter for a Quantum Magnetometer Based on Nitrogen-Vacancy Centers in Diamond

Quantum sensors based on solid-state defects, such as the nitrogen-vacancy (NV) center in diamond, offer very good room-temperature sensitivity, long-term stability, and the potential for calibration-free measurements. However, most quantum sensors still suffer from a bulky size and weight, low energy efficiency, and high costs, prohibiting their widespread use. Here, we present custom-designed chip-integrated microwave (MW) electronics for a miniaturized, low-cost, and highly scalable quantum magnetometer based on NV centers in diamond. The presented electronics include a quadrature phase-locked loop (QPLL) chip to generate the required local oscillator signal at around 7 GHz with a wide tuning range of 22% and a low phase noise (PN) of −122 dBc/Hz at 1-MHz offset from a 7-GHz carrier for broadband low-noise magnetometry. In addition, the magnetometer electronics comprise a 4-channel transmitter chip, which can provide currents up to 412 mApp into a custom-designed inductor over a wide frequency range from 6.4 to 8 GHz. In combination with a custom-designed coil, manufactured on a glass substrate for optical transparency, which features a large active area of (
$\pi { \times } 180 { \times }180~\mu \text {m}^{2}$
), this current is sufficient to produce strong MW magnetic fields up to
$B_{{1}} = (1/2) \cdot B_{\text {ac}} = 170~{\mu \mathrm {T}}$
, enabling pulsed optically detected magnetic resonance (ODMR) experiments. In proof-of-concept ODMR experiments, the presented chip-based spin control system produces fast Rabi oscillations of 5.49 MHz. The measured dc and ac magnetic field limits of detection (LOD) of the presented magnetometer are 32 nT/Hz
$^{\text {1/2}}$
and 300 pT/Hz
$^{\text {1/2}}$
, respectively.