Quantum Tunneling Detection of Two-photon and Two-electron Processes
  We analyze the operation of a quantum tunneling detector coupled to a coherent conductor. We demonstrate that in a certain energy range the output of the detector is determined by two-photon processes, two-electron processes and the interference of the two. We show how the individual contributions of these processes can be resolved in experiments. 
J. Tobiska, J. Danon, I. Snyman and Yu. V. Nazarov