We propose a detector of microwave photons that can distinguish the vacuum state, one-photon state, and the states with two or more photons. Its operation is based on the two-photon transition in a biased Josephson junction and detection occurs when it switches from a superconducting to a normal state. We model the detector theoretically. The detector performs with more than 90% success probability in several microseconds. The working frequency can be set at the design stage in the range from about 1 to 20 GHz.

• Received 2 April 2020
• Revised 6 October 2020
• Accepted 4 December 2020

DOI:https://doi.org/10.1103/PhysRevApplied.14.064063