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Radiation sensors based on the heating effect of absorbed radiation are typically simple to operate and flexible in terms of input frequency, so they are widely used in gas detection 1, security 2, terahertz imaging 3, astrophysical observations 4 and medical applications 5. Several important applications are currently emerging from quantum technology and especially from electrical circuits that behave quantum mechanically, that is, circuit quantum electrodynamics 6. This field has given rise to single-photon microwave detectors 7, 8, 9 and a quantum computer that is superior to classical supercomputers for certain tasks 10. Thermal sensors hold potential for enhancing such devices because they do not add quantum noise and they are smaller, simpler and consume about six orders of magnitude less power than the frequently used travelling-wave parametric amplifiers 11. However, despite great progress in the …