This was part of Mathematical Methods for Quantum Hardware
Readout problem in circuit QED
Alexandru Petrescu, INRIA
Wednesday, July 13, 2022
Abstract: In typical circuit quantum electrodynamics experiments, the quantum state of a superconducting qubit is measured by monitoring a readout resonator weakly and off-resonantly coupled to the qubit. As drive power is increased to achieve a higher-fidelity and faster measurement, unwanted transitions occur, which, for example, decrease the qubit’s energy relaxation time T1. In this talk, we focus on transmon qubits, and we present a time-dependent Schrieffer-Wolff perturbation theory that allows us to catalog nonlinear relaxation processes, and identify stimulated emission as one possible mechanism for spurious qubit relaxation during readout . Turning to numerical techniques, we address the related phenomenon of escape into unconfined states [2,3], and discuss a second mechanism for rate enhancement during measurement: by interactions between the states defining the qubit subspace, and higher-energy chaotic states within the Floquet spectrum.  A. Petrescu, M. Malekakhlagh, and H. E. T ̈ureci, Phys. Rev. B 101, 134510 (2020).  L. Verney, R. Lescanne, M. H. Devoret, Z. Leghtas, and M. Mirrahimi, Phys. Rev. Applied 11, 024003 (2019)  R. Shillito, A. Petrescu, J. Cohen, J. Beall, M. Hauru, M. Ganahl, A. G. M. Lewis, G. Vidal, and A. Blais, “Dynamics of transmon ionization” arXiv: 2203.11235 (2022).