We perform a detailed analysis of how an amplified interferometer can be used to enhance the quality of a dispersive qubit measurement, such as one performed on a superconducting transmon qubit, using homodyne detection on an amplified microwave signal. Our modeling makes a realistic assessment of what is possible in current circuit-QED experiments; in particular, we take into account the frequency-dependence of the qubit-induced phase shift for short microwaves pulses. We compare the possible signal-to-noise ratios obtainable with (single-mode) SU(1,1) interferometers with the current coherent measurement and find a considerable reduction in measurement error probability in an experimentally-accessible range of parameters.
@article{arxiv.1407.3059,
title = {Dispersive Qubit Measurement by Interferometry with Parametric Amplifiers},
author = {Sh. Barzanjeh and D. P. DiVincenzo and B. M. Terhal},
journal= {arXiv preprint arXiv:1407.3059},
year = {2015}
}