2023

Chen, Liangyu; Li, Hang Xi; Lu, Yong; Warren, Christopher W.; Križan, Christian J.; Kosen, Sandoko; Rommel, Marcus; Ahmed, Shahnawaz; Osman, Amr; Biznárová, Janka; Fadavi Roudsari, Anita; Lienhard, Benjamin; Caputo, Marco; Grigoras, Kestutis; Grönberg, Leif; Govenius, Joonas; Kockum, Anton Frisk; Delsing, Per; Bylander, Jonas; Tancredi, Giovanna

<p>High-fidelity and rapid readout of a qubit state is key to quantum computing and communication, and it is a prerequisite for quantum error correction. We present a readout scheme for superconducting qubits that combines two microwave techniques: applying a shelving technique to the qubit that reduces the contribution of decay error during readout, and a two-tone excitation of the readout resonator to distinguish among qubit populations in higher energy levels. Using a machine-learning algorithm to post-process the two-tone measurement results further improves the qubit-state assignment fidelity. We perform single-shot frequency-multiplexed qubit readout, with a 140 ns readout time, and demonstrate 99.5% assignment fidelity for two-state readout and 96.9% for three-state readout–without using a quantum-limited amplifier.</p>