AVS 72 Session TS-ThM: The Future of Temperature Sensing IV

Virtually every quantum technology needs to be operated at some level of low temperatures to generate and protect low energy quantum states.As a result, cryogenics has become a critical enabling tool in the race to develop quantum technologies.Yet little attention has been paid to the thermometry that allows us to quantify these low temperatures.As an example, most users of a dilution refrigerator simply take for granted that the resistive temperature sensor they use to measure millikelvin temperatures is accurate (and actually represents their experimental temperature).A such, we believe that a renewed focus must be put on primary temperatures sensors in the sub-kelvin regime to ensure that quantum technologies and their enabling cryogenics can be accurately measured and compared between laboratories.To this end, we are working on a type of mechanical noise thermometry using the techniques of cavity optomechanics.I will provide the background and context of this temperature sensor and where we are in its development.

Temperature is one of the most commonly measured physical quantities and influences nearly every physical, chemical, and biological process. Photonic and quantum-based approaches have the potential to transform practical thermometry by enabling in-situ traceability without requiring sensor removal for recalibration. A further advantage of these optical methods is their compatibility with silicon photonics, allowing on-chip integration thus to have the potential to radically improve thermal management of semi-conductor devices.

In this presentation, I will give an overview of the progress of European Partnership in Metrology Joint Research Project: Photonic and Quantum Sensors for Practical Integrated Primary Thermometry (PhoQuS-T) [1]. This project aims to develop integrated optical practical primary thermometry from 4 K to 500 K to enable in-situ traceability for practical applications.To achieve this, we combine several techniques: photonic thermometry using ring resonators; optomechanical noise thermometry and quantum correlation thermometry with opto-mechanical resonators. In addition, key challenges such as robust packaging over a wide temperature range are being addressed, along with metrological validation of the developed sensors and the exploration of future application possibilities.

At the current stage of the project, recent progress in photonic thermometry and optical noise thermometry from 4 K to 300 K, using 1D- and 2D- optomechanical sensors, will be presented. The next steps toward self-calibration using quantum thermometry (quantum correlation techniques [2]) will also be discussed. An overview of advances in high-resolution photonic sensors based on ring resonators operating over an extended temperature range (80 K to 500 K) will be given, along with updates on the development of a novel active thermometry approach [3]. Progress in packaging techniques (including gluing, welding, and mechanical support) for the developed sensors will also be presented.

Finally, developments toward practical application of such photonic sensors (including temperature monitoring of photonic integrated chips for optical clocks and assigning temperature in quantum-based pressure measurements) will be discussed.

References:

[1] https://www.mdpi.com/2673-8244/5/3/44

[2] https://www.science.org/doi/10.1126/science.aag1407

[3] https://doi.org/10.1098/rsta.2024.0459

Accurate temperature sensing at the nanoscale remains a central challenge for emerging quantum, photonic and nanomechanical technologies, where local heating, weak thermal anchoring and limited calibration accuracy can strongly affect device performance. Optomechanical systems offer a route to temperature sensing based on the thermal occupation of mechanical modes, enabling local, contactless and potentially self-calibrated thermometry through the optical readout of mechanical motion.

Here we present the design and first experimental realization of a two-dimensional silicon optomechanical crystal engineered as a platform for temperature sensing across the transition from the classical thermal regime toward the quantum regime. The device integrates a telecom C-band optical cavity and a co-localized GHz radial-breathing mechanical mode within a two-dimensional phononic shield. This architecture combines strong optical–mechanical confinement with improved thermal anchoring to the substrate compared with conventional one-dimensional optomechanical cavities, reducing absorption-induced heating while preserving high displacement sensitivity.

The geometry was optimized using three-dimensional simulations and machine-learning-assisted parametric sweeps to achieve operation in the resolved-sideband regime, high optical and mechanical quality factors, and strong optomechanical coupling. These characteristics enable sensitive monitoring of the mechanical noise spectrum as a function of temperature and provide the basis for sideband-resolved thermometry at low phonon occupation. In this regime, the Stokes and anti-Stokes sidebands provide a direct route to absolute quantum thermometry, since their asymmetry is determined by the mean phonon population rather than by an external thermal calibration.

We discuss how this two-dimensional optomechanical platform can be used for temperature sensing from elevated temperatures down to cryogenic conditions, with particular emphasis on quantifying local optical heating, calibrating phonon occupation, and approaching the quantum ground state. By combining heterodyne sideband readout, optomechanical cooling and sideband-asymmetry thermometry, the device provides a route toward quantum-referenced nanoscale temperature sensing. These results position two-dimensional silicon optomechanical crystals as a promising integrated platform for future temperature sensors operating beyond conventional calibration limits.

Acknowledgements

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