Yinghao Ho

Achieving the full potential of quantum computing will require the development of quantum gates—circuits that carry out fundamental operations—with much higher fidelity than is currently available. An average gate fidelity surpassing 99.9%, for example, would enable not only efficient fault-tolerant quantum computing with error correction but also effective mitigation of errors in current noisy intermediate-scale quantum devices.

Tunable couplers in superconducting quantum computers have enabled fast and accurate two-qubit gates, with reported high fidelities over 99% in various architectures and gate-implementation schemes. However, there are few tunable couplers whose performance in multiqubit systems is clarified, except for the most widely used one: single-transmon coupler (STC).

Generation of logical zero states encoded with a quantum error-correcting code is the first step for fault-tolerant quantum computation but requires considerably large resource overheads in general. To reduce such overheads, we propose an efficient encoding method for the distance-three, nine-qubit surface code and show its fault tolerance. This method needs no measurement, unlike other fault-tolerant encoding methods. Moreover, this is applicable to a one-dimensional qubit array.