Title: Error correction of a logical quantum bit beyond the break-even point

Abstract: In order for quantum computers to surpass classical ones in useful tasks, the accuracy of logical operations on quantum bits (qubits) must be made robust to noise that affects the underlying physical system. Rather than reducing the noise reaching qubits, quantum error correction aims at preventing it from causing logical errors. This approach is based on 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 adequately encoded non-locally in the larger Hilbert space of a composite system, it is possible, during a limited time, to detect and correct noise-induced evolution before it corrupts the encoded information. We will present an experiment based on a superconducting cavity and a transmon synthetic atom – the latter employed here as an auxiliary non-linear element [1] – that implements autonomous error correction, incorporating novel primitive operations [2] and feedback control based on reinforcement learning [3]. Recently, we have stabilized in real-time a logical qubit manifold spanned by the so-called Gottesman-Kitaev-Preskill grid states, reaching a collective correction efficiency such that the lifetime of the encoded information was prolonged by more than a factor of two beyond the lifetime of the best physical qubit composing our system, including the error-correction mechanism [4]

[1] Campagne-Ibarcq, Eickbusch, Touzard, et al., Nature 584, 368-372 (2020).

[2] Eickbusch et al., Nature Physics 18, 1464 (2022).

[3] Sivak et al., Phys. Rev. X 12, 011059 (2022).

[4] Sivak et al., Nature 616, 50-55 (2023).

† Also affiliated part-time with Google Quantum AI

A light lunch will be served outside of Maeder Auditorium at noon.