Superconducting germanium-based hybrid bolometers for microwave photon detection

Detecting microwave radiation, down to the single photon level, is a central challenge in modern quantum technologies.

In recent years, a promising route has been envisioned, largely inspired by an ubiquitous technique in high-energy photon detection: bolometry.

Its principle relies on energy dissipation of incident photons in a thermal detector, the temperature of which is monitored.

This calorimetric technique allows for single photon detection in the infrared band or above, but its application to the microwave domain is challenging, since individual photons carry orders of magnitude less energy.

However, superconducting nanoscale thermal detectors at millikelvin temperatures have recently shown their great potential for sensing extremely low radiation signals, as well as small instantaneous energy releases.

Although still challenging at present, considering the calorimetric detection of single microwave photons emitted by a qubit is within reach.

A very recent work demonstrated the single-shot read out of a qubit state, by measuring in situ the magnitude of the readout microwave signal, using a superconducting bolometer.In this project, the researcher will develop and measure nano-bolometers based on silicon-germanium heterostructures, and infer limiting factors in their sensitivity.

These bolometers will be co-integrated with germanium qubits to benchmark their performances as compared to standard dispersive detection schemes.The researcher will also push these detectors' sensitivity beyond the state of the art, with the final goal to detect single microwave photons.

This will allow for wide-ranging and groundbreaking applications, including alternative qubit readout schemes but also quantum thermodynamics experiments in circuit-QED architectures.