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Photodetector is an essential instrument in quantum optics and is extensively used for various applications across the diverse domain of quantum technologies. A Josephson photomultiplier (JPM) is an on-chip microwave detector that is fully compatible with superconducting circuit QED architecture. Essentially, it is a phase qubit that operates as an absorbing single-photon threshold detector, delivering a "click" only when at least one photon is present in the measured mode. We propose an extension [1] to the JPM that transforms it into a two-photon threshold detector, which absorbs a pair of photons and "clicks" only when there are at least two photons in the measured mode. To achieve this, the JPM is capacitively coupled to a resonator dimer—two lumped-element resonators that interact via an asymmetric SQUID. The inherent nonlinearity of the SQUID coupler enables us to engineer a nonperturbative two-photon coupling [2] between the resonator modes. This nonlinear coupling facilitates the conversion of a photon pair from one resonator into a single photon in another resonator, enabling a selective response to quantum states with at least two photons.
This work was supported by the National Research Foundation of Ukraine through Project No. 2023.03/0165, Quantum correlations of electromagnetic radiation.
- E. V. Stolyarov and R. A. Baskov, Phys. Rev. Res. 7, 033263 (2025).
- E. V. Stolyarov, V. L. Andriichuk, and A. M. Sokolov, Phys. Rev. B 111, 214517 (2025).
