Work Packages
The research is divided into four technical work packages
Progress beyond the state of the art
This project aims at a paradigm shift in temperature measurement not only by producing a practical primary thermometer (in-situ traceability at point of measurement), but also by adopting a photon-based approach with a sub-µm scale spatial resolution. Within this ambitious objective, significant advance will be made building on the achievements of the EMPIR JRP 17FUN05 PhotOQuanT, where the state-of-the-art optomechanical and photonic resonators were fabricated demonstrating optomechanical noise thermometry (at cryogenic temperatures) and photonic thermometry (around room temperature). State of the art will be advanced through using integrating photonic technologies which will combine different techniques onto a single device for a first practical quantum primary thermometer from cryogenics to 500 K. Quantum thermometry will provide a quantum reference for the optical noise thermometry operating in 4 – 300 K range, while sub mK resolution and wide operational range to 500 K are provided through photonic thermometry. In this project, for the first time such a practical primary temperature sensor will be developed, validated and its quantum applications demonstrated. For this breakthrough, all scientific/technical work in the JRP requires significant progress beyond state of the art.
WP1: Development of optical noise thermometry from 4 K to 300 K and quantum thermometry below 10 K
In the EMPIR JRP 17FUN05 PhotOQuanT, optomechanical noise thermometry was demonstrated over 4 -300 K with 1D-structures suffering from self-heating. New 1D/2D geometries (to reduce the self-heating by a factor of 10) and arrays of resonators (to reduce uncertainty over a large temperature range) will be developed. Quantum correlation thermometry facilitates integrated, nanoscale, magnetic-field insensitive primary thermometry as demonstrated at NIST (2017). Here, advantage will be taken of this technique at cryogenic temperatures (below 10 K) to provide a quantum reference for a high-performance noise thermometry on the same optomechanical structure operating in 4 – 300 K range (with target uncertainty 0.1 K).
WP2: Advanced photonic thermometry from 80 K to 500 K
Photonic thermometry is based on the thermo-optic effect and offers very high sensitivity (70 pm/K) and sub mK resolution (shown in EMPIR JRP 17FUN05 PhotOQuanT project). This project will go beyond the state of art, firstly, by exploring enhanced read-out techniques and by improving the device design to extend the operation range (80 K – 500 K) exploring Si and SiN; and secondly, by developing a non-Si based novel active thermometry approach (combining laser source and photonic sensor) as a step towards the fully integrated device.
WP3: Robust fibre to chip coupling packaging solutions over 4 – 500 K temperature range
The free-space coupling drastically limits the practical application of the optical sensors. This project will go beyond the state of the art by developing different approaches (gluing, welding, mechanical) for packaging and robust fibre-to-chip coupling over a large temperature range (4 K – 500 K) to mitigate for thermal expansion mismatch between fibre, chip and adhesive material over temperature range while catering to the requirements of optomechanical and photonic sensors.
WP4: Metrological validation and applications
Photonic thermometry and optomechanical thermometry are both recent emerging technologies. Nowadays, NIST demonstrated a proof of principle of the quantum correlation technique to calibrate thermal noise versus quantum noise in an optomechanical resonator. The first results of EMPIR JRP 17FUN05 PhotOQuanT project on optomechanical noise thermometry were mainly limited by a strong self-heating effect and the photonic thermometry has been demonstrated around room temperature with a standard deviation about 10 mK. Recently, uncertainties of 10 mK could be demonstrated by the Canadian NMI. The progress introduced in this project (2D optomechanical resonator with self-heating divided by at least 10, advanced photonic resonators enabling a broad temperature range, from 80 K to 500 K) should allow the consortium to improve the state of the art with these emerging technologies. Within this project, the metrological validation will be performed establishing traceability to ITS-90 over their full temperature range together with computation of the respective uncertainty budgets (with target uncertainties for optomechanical sensors of 0.1 K from 4 K to 300 K and for passive photonic sensors of 25 mK from 80 K to 500 K and 5 mK from 283 K to 363 K). In addition, in this project, the application of these sensors to measure the temperature drift of ion traps, without interference with their operation will be explored. The application of the photonic thermometry for the temperature assignment in the photon-based approach for pressure measurements will open the way towards an all-optical quantum-based pressure standard.
