Coherent errors and readout errors in surface code

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Coherent errors and readout errors in surface code
2023. 03. 10. 10:15
BME building F, seminar room of the Dept. of Theoretical Physics
János Asbóth (BME/Wigner)
The surface code is the leading candidate for quantum error correction. However, the level of protection it offers against coherent errors, i.e., nonfluctuating phase rotations on the physical qubits, is not well known. We consider[1] the combined effect of readout errors and coherent errors on the surface code. We use a recently developed numerical approach, via a mapping of the physical qubits to Majorana fermions[2]. We find a threshold for this combination of errors, with an error rate close to the threshold of the corresponding incoherent error channel (random Pauli-Z and readout errors). Below the threshold, scaling up the code leads to the rapid loss of coherence of errors on the logical level, but error rates that are greater than those of the corresponding incoherent error channel. We also vary the coherent and readout error rates independently, and find that the surface code is more sensitive to coherent errors than to readout errors. Our work extends the recent results on coherent errors with perfect readout [2] to the experimentally more realistic situation where readout errors also occur.
[1]: A Marton and JK Asboth: Coherent errors and readout errors in surface code, arXiv:2303.04672
[2]: S Bravyi et al: Correcting coherent errors with surface codes, npj Quantum Information, vol. 4, no. 55 (2018)