Quantum systems operating at room temperature offer new ways to detect weak forces and magnetic fields. In this talk, I will present recent work from our group at DTU addressing mechanical and spin-based systems.
In the first part, I will address ultrahigh-Q factor membrane oscillators, and I will show how a nonlinear readout in an optical microcavity removes thermal intermodulation noise and improves the signal-to-noise ratio by nearly 10 dB. Next, I will show how such membrane oscillators can be magnetically functionalized with nanopillars directly grown on the device. The Q-factor of the membrane remains almost unchanged while the magnetization is mapped out and confirmed using a nitrogen-vacancy (NV) scanning magnetometer. In the last part of the talk I will turn towards NV centers in diamond and present a laser-scanning technique for fast magnetic-field imaging, which we plan using for passive recording of magnetic fields from neuronal activity in living brain tissue.