Period-doubling-bifurcation readout for a Josephson qubit

TL;DR

This paper introduces a novel threshold detector based on period-doubling bifurcation in a Josephson circuit, enabling sensitive quantum state readout with potential advantages over existing amplifiers.

Contribution

It proposes a new readout method utilizing parametric bifurcation in a Josephson circuit, enhancing quantum measurement sensitivity.

Findings

Demonstrates sharp oscillation onset at half-drive frequency

Shows potential for improved qubit state detection

Compares bifurcation characteristics with conventional amplifiers

Abstract

We propose a threshold detector with an operation principle, based on a parametric period-doubling bifurcation in an externally pumped nonlinear resonance circuit. The ac-driven resonance circuit includes a dc-current-biased Josephson junction ensuring parametric frequency conversion (period-doubling bifurcation) due to its quadratic nonlinearity. A sharp onset of oscillations at the half-frequency of the drive allows for detection of small variations of an effective inductance and, therefore, the read-out of the quantum state of a coupled Josephson qubit. The bifurcation characteristics of this circuit are compared with those of the conventional Josephson bifurcation amplifier, and its possible advantages are discussed.