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. In this work, we report on a two-qubit gate that achieves that milestone and sustains it for 12 h.
Superconducting qubits, with their ease of scalability and controllability, are prime candidates for building quantum processors. One type known as a transmon is renowned for its high coherence and ease of manufacturing and is thus already widely embraced in academia and industry. In general, single-qubit gates need negligible coupling between two transmon qubits, whereas two-qubit gates require a large coupling. This necessitates a coupling mechanism that can be tuned to both nearly zero and a very large value.
Various coupling schemes based on transmons have been shown to address this issue. Our work focuses on an innovative coupler known as the double-transmon coupler (DTC), which has been only theoretically proposed. We report the first experimental realization of the DTC, achieving gate fidelities of 99.9% for two-qubit gates and 99.98% for single-qubit gates, demonstrated by using two transmons coupled by the DTC.
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