Stochastic Amplifier Based on Superconducting Interferometer with 4-Terminal Josephson Junction for Flux Qubit State Readout

Abstract

This paper proposes one of possible solutions to arrange the weak continuous measurements of the state of the flux qubit based on a superconducting interferometer ring, with a stochastic amplifier which provides the minor back action.The amplifier exploits the stochastic resonance (SR) effect and is embodied as a superconducting interferometer ring incorporating the four-terminal (4-t) Josephson junction . The two leads of the 4-t Josephson junction are closed by the amplifier-interferometer ring while the rest two are connected to the superconducting magnetic antenna (flux transformer) that senses the flux qubit state. In this arrangement, a variation of the qubit flux which corresponds to a certain qubit state superposition results in a change in the antenna loop current. Further, the stochastic amplifier gain, as it will be shown below, depends on the antenna loop current thus monitoring the cubit state.