On-chip thermometry at millikelvin temperatures for quantum-classical electronics co-integration

Quantum computing has the potential to revolutionize information processing by performing computations beyond the reach of classical computers. This will require the operation of quantum processors containing millions of extremely sensitive qubits, located inside dilution refrigerators and operated at temperatures near 10 millikelvin. Current experimental systems, however, are limited to only a few hundred qubits. This is due in part to the input-output bottleneck, which greatly limits qubit control at scale.

Cryogenic CMOS circuits, closely integrated with quantum circuits, have been proposed as a solution to alleviate this input-output bottleneck and allow for the operation of large-scale quantum processors [1]. Achieving this is especially challenging, due to the extremely stringent thermal and noise requirements of quantum bits and of the cryogenic environment. Accurate temperature sensing is therefore critical for the characterization, validation and optimization of such chips at deep cryogenic temperatures. However, conventional temperature sensors often lack the required sensitivity or resolution and cannot be directly integrated on CMOS chips for characterization.

In this Master thesis, you will investigate CMOS-compatible on-chip thermometry techniques suitable for millikelvin temperatures, with a focus on semiconductor devices such as diodes or bipolar junction transistors (BJTs) [2]. This work will consist of cryogenic electrical measurements in a dilution refrigerator, performed at temperatures down to 10 mK. It could include the development of calibration and measurement protocols for the accurate extraction of the local temperature at different areas of a chip. The thesis aims to quantify the impact of cryogenic circuits operating in different modes on the local temperature, both within and outside the chip, and to assess the relevance of thermal effects for closer integration with quantum processors.

Required background: Electrical engineering, Physics

Type of work: 20% literature, 40% measurements and experiments, 40% data analysis

Promotor: Bart Soree

Daily advisors: Liam Fallik, Anton Potočnik

References:

[1] Potočnik, A. How to scale the electronic control systems of a quantum computer. Nat Electron 8, 3–4 (2025). https://doi.org/10.1038/s41928-024-01331-9

[2] Grayson M. Noah et. al. CMOS on-chip thermometry at deep cryogenic temperatures. Appl. Phys. Rev. 11, 021414 (2024). https://doi.org/10.1063/5.0190040