Messages are often transmitted with light, the quantum unit of it being the photon. In the microwave regime used in our superconducting circuits, detecting a single itinerant photon is however challenging, as it possesses up to 5 orders of magnitude less energy than its optical counterpart. In this work, we show how to transfer the information of the flying photon’s passage into an excitation of a stationary artificial atom, a qubit. By reading out the state of the latter, we acquire knowledge about the photon’s presence without destroying it. This ‘non-demolition’ aspect opens up new possibilities of placing the detector in the middle of the photon’s path, and letting it propagate towards another destination.
Phys. Rev. X 8, 021003 (2018)