Liangyu Chen, Simon Pettersson Fors, Zixian Yan, Anaida Ali, Tahereh Abad, Tangyou Huang, Amr Osman, Eleftherios Moschandreou, Benjamin Lienhard, Sandoko Kosen, Hang-Xi Li, Daryoush Shiri, Tong Liu, Stefan Hill, Abdullah-Al Amin, Robert Rehammar, Mamta Dahiya, Andreas Nylander, Marcus Rommel, Anita Fadavi Roudsari, Marco Caputo, Leif Grönberg, Joonas Govenius, Miroslav Dobšíček, Michele Faucci Giannelli, Anton Frisk Kockum, Jonas Bylander, Giovanna Tancredi
Abstract On-demand qubit-state initialization is a prerequisite for quantum computation. We demonstrate such a protocol in a device consisting of fixed-frequency transmon qubits pair-wise coupled via tunable couplers — an architecture that is also compatible with the surface code. We use tunable couplers to transfer any undesired qubit excitation to the readout resonator of the qubit, from which this excitation decays into the feedline. In total, the combination of multi-level qubit reset, leakage reduction, and coupler reset takes only 88 ns to complete. Our reset scheme is fast, unconditional, and achieves fidelities above 99%, thus enabling fixed-frequency qubit architectures as future implementations of fault-tolerant quantum computers.