We show how to use two-mode squeezed light to exponentially enhance cavity-based dispersive qubit measurement. Our scheme enables true Heisenberg-limited scaling of the measurement, and crucially, is not restricted to small dispersive couplings or unrealistically long measurement times. It involves coupling a qubit dispersively to two cavities, and making use of a symmetry in the dynamics of joint cavity quadratures (a so-called quantum-mechanics-free subsystem). We discuss the basic scaling of the scheme and its robustness against imperfections, as well as a realistic implementation in circuit quantum electrodynamics.
@article{arxiv.1502.00607,
title = {Heisenberg-limited qubit readout with two-mode squeezed light},
author = {Nicolas Didier and Archana Kamal and William D. Oliver and Alexandre Blais and Aashish A. Clerk},
journal= {arXiv preprint arXiv:1502.00607},
year = {2015}
}