We have realized a new interaction between superconducting qubits and a readout cavity that results in the displacement of a coherent state in the cavity, conditioned on the state of the qubit. This conditional state, when it reaches the cavity-following, phase-sensitive amplifier, matches its measured observable, namely the in-phase quadrature. In a setup where several qubits are coupled to the same readout resonator, we show it is possible to measure the state of a target qubit with minimal dephasing of the other qubits. Our results suggest novel directions for faster readout of superconducting qubits and implementations of bosonic quantum error-correcting codes.
@article{arxiv.1809.06964,
title = {Gated conditional displacement readout of superconducting qubits},
author = {S. Touzard and A. Kou and N. E. Frattini and V. V. Sivak and S. Puri and A. Grimm and L. Frunzio and S. Shankar and M. H. Devoret},
journal= {arXiv preprint arXiv:1809.06964},
year = {2019}
}