Detecting low-energy microwave photons emitted by superconducting qubits

Detecting low-energy microwave photons emitted by superconducting qubits

Researchers from Aalto University propose a new approach to measure the energy of single microwave photons. These low energy quanta are emitted by artificial quantum systems such as superconducting qubits. Detecting them continuously has been challenging but would be useful in quantum information processing and other quantum technologies.

A photon is produced when a superconducting qubit transits between states, radiating energy into its environment. The researchers capture the tiny energy of this photon by transferring it into heat. The new technique relies on splitting the energy of a photon across two independent heat baths and making measurements using two uncoupled detectors at once. This would significantly enhance the signal-to-noise ratio, making it easier to detect an absorption event and its energy.

The researchers explain that many fundamental questions remain open but this would be the first time the energy of a photon is split into two different thermal detectors and observed. 

The researchers introduced the extremely sensitive calorimeter two years ago, and Physics World listed the calorimeter as one of the quantum highlights of 2020. (

The study has been published in Physical Review X.

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