Quantum efficiency of a microwave photon detector based on a current-biased Josephson junction

TL;DR

This paper evaluates the quantum efficiency of a microwave photon detector using a current-biased Josephson junction, demonstrating that such devices can achieve over 80% efficiency despite modest coherence.

Contribution

It models the detector's quantum efficiency considering environmental coupling and provides a detailed analysis of how efficiency depends on various parameters.

Findings

Quantum efficiency exceeds 80% for modest coherence junctions

Efficiency depends on detection time, bias current, and relaxation time

Theoretical framework for optimizing microwave photon detection

Abstract

We analyze the quantum efficiency of a microwave photon detector based on a current-biased Josephson junction. We consider the Jaynes-Cummings Hamiltonian to describe coupling between the photon field and the junction. We then take into account coupling of the junction and the resonator to the environment. We solve the equation of motion of the density matrix of the resonator-junction system to compute the quantum efficiency of the detector as a function of detection time, bias current, and energy relaxation time. Our results indicate that junctions with modest coherence properties can provide efficient detection of single microwave photons, with quantum efficiency in excess of 80%.