Optomechanical thermometry

The aim of this project is to develop an on-chip quantum primary thermometer based on the innovative concept of nanoscale optomechanical crystal thus bridging the gap between long-term stability and ultimate accuracy. Meanwhile and on the same chip, photonic crystals will assess a relative temperature with respect to the absolute one given by the optomechanical counterpart offering a self-calibrated thermometer over a large range of temperature (from 100mK to 300K).

The “Mise en Pratique of the kelvin” unit relies on both practical scale thermometry and primary thermometry (since 2018, the thermodynamic temperature is based on the fixed value of the Boltzmann constant). Quantum optomechanics, based on the reading of the mechanical motion of an object thanks to light, is highly susceptible to offer an answer to this problem as it now provides a toolbox of new technologies using high sensitive quantum measurements.

The team develop thermometry read-out protocols for the optomechanical sensors based on three complementary optical measurements (photonics, noise and quantum thermometry) and working on different but overlapping temperature ranges. They all can be realized on the same device with the same interrogating interface and probing optical and mechanical degrees of freedom. Photonic thermometry will be able to reach a sensitivity of the order of the mK in the 50—300K range. Below 10K we will develop a readout method to target a primary quantum measurement exploiting quantum correlations and providing an absolute measurement. Noise thermometry, based on monitoring the thermal noise of a harmonic oscillator will bridge the gap between Photonic (>50 K) and Quantum thermometry (<10K) as it theoretically presents a perfect linearity on the full temperature range.