Andrii M. Sokolov

Two-photon coupling via Josephson element I: Breaking the symmetry with magnetic fields

  1. E. V. Stolyarov,
  2. V. L. Andriichuk,
  3. and Andrii M. Sokolov
We consider a coupling element based on a symmetric superconducting quantum interference device (SQUID) and show that it mediates a two-photon interaction. This and other inductive
interactions can be switched off in situ. We derive the system Hamiltonian for coupled resonator and rf SQUID. The rf SQUID dwells in the vicinity of its metastable well holding a number of energy states and acts as an artificial atom. We discuss how the Josephson symmetry breaks owing to magnetic fields in the superconducting loops. We assess that the two-photon coupling strength reaches 18 MHz which can exceed the single-photon capacitive interaction in the coupler.
arxiv pdf

A superconducting detector that counts microwave photons up to two

  1. Andrii M. Sokolov,
  2. and Frank K. Wilhelm
We propose a detector of microwave photons which 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. It is sensitive for the 8.2GHz photons. The working frequency could be set at the design stage in the range from about 1GHz to 20GHz.
arxiv pdf