The PhotOQuanT project aims to develop optomechanical and photonic sensors for future temperature standards
Photonic sensors use light-matter interaction to measure temperature and other physical quantities via temperature-dependent material properties. A particularly promising new development is the possibility of using optomechanical sensors to produce quantum primary standards. Photonic and optomechanical temperature sensors enable a spatial resolution adapted for the measurement of temperature at micrometer length scale where usual sensors are unsuitable. This project develops photonic and optomechanical sensors for the measurement of temperature at micrometre length scale. These sensors will have optimised sensitivity as well as robustness to mechanical constraints and chemical species, and will be of prime importance for the future dissemination of the kelvin following its forthcoming re-definition in 2018.
THE NEED FOR THE PROJECT
Temperature is probably the most important physical variable of state, influencing almost every physical, chemical, and biological process. Surprisingly, the world's most accurate temperature sensors, standard platinum resistance thermometers (SPRTs), rely on antiquated technologies that do not lend themselves to miniaturisation, portability, or wide dissemination. Moreover, the platinum resistance thermometers are sensitive to mechanical shock, thermal stress and environmental variables such as humidity and chemical contaminants that cause irreproducibility and drifts. These fundamental limitations have stimulated the quest for improved temperature sensors. Photonic temperature sensors are inexpensive, lightweight, portable, and resistant both to mechanical shock and to electromagnetic interferences. However, such sensors require the development of specific calibration and characterisation systems to provide traceability where usual macroscopic metrological standards are not applicable.
To achieve the ambitious requirements of the project, the following objectives will be met:
To design and fabricate different photonic and optomechanical devices dedicated to temperature metrology at the nano- and micro-scale: photonic crystal cavities, micro-rings, micro-disks and membrane resonators with high optical (for photonic sensors: Qo > 105; for optomechanical sensors: Qo > 108) and mechanical quality factors (Q > 104).
To investigate the optical and mechanical performance (photo-elastic properties) of several silicon- and diamond-based materials, and their influence on the quality factor of the optical and mechanical resonators. To study the viability of using these materials in quantum optomechanical resonators.
To characterize the metrological repeatability, sensitivity and stability of both photonic and opto-mechanical devices, and demonstrate quantum-based read-out protocols for opto-mechanical devices as quantum primary temperature standards up to ambient temperature.
To develop methods for calibrating the developed mesoscopic sensors traceable to the International Temperature Scale of 1990 (ITS-90) including the evaluation of the uncertainty. Target uncertainties are below 1 mK for photonic sensors and below 1 K for optomechanical sensors in quantum regime (below 10 K).
To facilitate the adoption of the technology developed in the project, by end users of thermometry and nanoscale technology.
PROGRESS BEYOND THE STATE OF THE ART
Photonic silicon resonators will be developed with the aim to outperform prior technologies by enhancing microscale sensor design, and using materials with improved stiffness and thermal conductivity. They will not only be more accurate, but also smaller, more robust and less sensitive to shocks and external variations than the more macroscopic platinum resistance thermometers.
PhotoQuanT is intended not only to design and construct photonic and optomechanical sensors but to study their temperature systematic effects and the quantum regime itself.
A procedure for quantum scale sensor calibration will be developed for the first time, where optomechanical resonator are calibrated at low temperature by linking them to primary quantum standards, and thermal noise thermometry is used to extend the temperature range towards room temperature without the need for further calibration.
Furthermore, a full uncertainty budget of these high-performance temperature sensors will be provided, that has not been reported yet for optomechanical resonators.
The mesoscopic sensors developed in this project will enhance the reliability of temperature measurement for applications in fields such as transportation industry, space instrumentation, engine monitoring, power plant safety and consumer electronics. PhotOQuanT also pave the way to high accuracy temperature measurement on a mesoscopic scale. With an improved robustness and sensitivity, photonic sensors could replace standard platinum resistance thermometers.