The Josephson Bifurcation Amplifier for Quantum Measurements

TL;DR

The paper introduces a Josephson bifurcation amplifier designed for quantum bit readout, offering high speed, sensitivity, and low back-action, demonstrated through experiments with nanofabricated Al junctions.

Contribution

It presents a novel amplifier based on Josephson junction bifurcation, achieving theoretical performance in quantum measurement applications.

Findings

Successful demonstration of bifurcation amplification in Al junctions

Achieved high sensitivity and low back-action in measurements

Performance matches theoretical predictions

Abstract

We have constructed a new type of amplifier whose primary purpose is the readout of superconducting quantum bits. It is based on the transition of an RF-driven Josephson junction between two distinct oscillation states near a dynamical bifurcation point. The main advantages of this new amplifier are speed, high-sensitivity, low back-action, and the absence of on-chip dissipation. Using pulsed microwave techniques, we demonstrate bifurcation amplification in nanofabricated Al junctions and verify that the performance predicted by theory is attained.