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.
@article{arxiv.1101.2712,
title = {Period-doubling-bifurcation readout for a Josephson qubit},
author = {Alexander B. Zorin and Yuriy Makhlin},
journal= {arXiv preprint arXiv:1101.2712},
year = {2015}
}