Individual quanta of these fields are photons with energy a few million times smaller than the energy of an optical photon and are extremely hard to detect. A promising device for microwave photon detection is based on Josephson junctions. Even a single microwave photon with tiny energy is sufficient to switch a junction from the superconducting to voltage state, and detection of a photon reduces to observation of voltage pulses across the junction.
In this talk, I will present a theoretical model of a Josephson junction interacting with a quantized electromagnetic field and show that such Josephson photon detectors have relatively high efficiency of detection of microwave photons. I will discuss application of such detectors to qubit readout for quantum information processing and to studies of photon emission statistics by quantum electronic devices.