Nanokelvin-resolution thermometry with a photonic microscale sensor at room temperature

Ultrahigh-resolution thermometry is critical for future advances in bio-calorimetry 1 , 2 , sensitive bolometry for sensing 3 and imaging 4 , as well as for probing dissipation in a range of electronic 5 , optoelectronic 6 and quantum devices 7 . In spite of recent advances in the field 8 – 11 , achieving high-resolution measurements from microscale devices at room temperature remains an outstanding challenge. Here, we present a band-edge microthermometer that achieves this goal by relying on the strong, temperature-dependent optical properties of GaAs at its absorption edge 12 – 14 . Specifically, using a suspended asymmetric Fabry–Pérot resonator and a wavelength-stabilized probe laser we demonstrate a thermoreflectance coefficient of >30 K −1 , enabling measurements with a thermometry noise floor of ~60 nK Hz −1/2 and a temperature resolution of <100 nK in a bandwidth of 0.1 Hz. The advances presented here are expected to enable a broad range of studies and applications in calorimetry and bolometry where miniaturized high-resolution thermometers are required.