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Abstract: Error correction of a logical qubit

Speaker: Michel Devoret

The accuracy of logical operations on quantum bits (qubits) must be improved for quantum computers to surpass classical ones in useful tasks. To that effect, quantum information needs to be made robust to noise that affects the underlying physical system. Rather than suppressing noise, quantum error correction aims at preventing it from causing logical errors. This approach derives from the reasonable assumption that noise is local: it does not act in a coordinated way on different parts of the physical system. Therefore, if a logical qubit is encoded non-locally, it is possible, during a limited time, to detect and correct noise-induced evolution before it corrupts the encoded information. We present an experiment based on superconducting cavities and a transmon artificial atom – the latter employed here as an ancillary non-linear element [1] – that implements autonomous error correction, incorporating novel operations [2] and feedback control based on reinforcement learning [3]. Recently, we have stabilized in real-time a logical qubit manifold spanned by Gottesman-Kitaev-Preskill grid states, reaching a correction efficiency such that the lifetime of the encoded information was prolonged by a factor of two beyond the lifetime of the physical qubits composing our system.

[1] Campagne-Ibarcq, Eickbusch, Touzard, et al., Nature 584, 368-372 (2020).
[2] Eickbusch et al., arXiv:2111.06414,  to appear in Nature Physics (2022).
[3] Sivak et al., arXiv:2104.14539,  Phys. Rev. X 12, 011059 (2022).