Fast High-Fidelity Quantum Nondemolition Qubit Readout via a Nonperturbative Cross-Kerr Coupling
17 pags., 9 figs., 3 tabs., 5 apps. ; Qubit readout is an indispensable element of any quantum information processor. In this work, we experimentally demonstrate a nonperturbative cross-Kerr couplingbetween a transmon and polariton mode which enables an improved quantum nondemolition (QND) readout for superconducting qubits. The new mechanism uses the same experimental techniques as the standard QND qubit readout in the dispersive approximation, but due to its nonperturbative nature, it maximizes the speed, the single-shot fidelity, and the QND properties of the readout. In addition, it minimizes the effect of unwanted decay channels such as the Purcell effect. We observe a single-shot readout fidelity of 97.4% for short 50-ns pulses and we quantify a QND-ness of 99% for long measurement pulses with repeated single-shot readouts. ; R. D. and S. L. acknowledge support from Fondation CFM pour la recherche. R. D., V. M., and O. B. acknowledge support from ANR REQUIEM (ANR-17-CE24-0012-01). J. J. G.-R. and T. R. acknowledge support from Project No. PGC2018-094792-B-I00 (MCIU/ AEI/FEDER, UE) and CAM/FEDER Project No. S2018/ TCS-4342 (QUITEMAD-CM). T. R. further acknowledges funding from the EU Horizon 2020 program under the Marie Skłodowska-Curie Grant Agreement No. 798397. S. L. acknowledges the Agence Nationale de la Recherche under the program Investissements d'avenir (ANR-15-IDEX02). K. B. and J. D. acknowledge the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 754303. J. P. acknowledges grant from the Laboratoire d'excellence LANEF in Grenoble (ANR-10-LABX-51-01).
