State preservation by repetitive error detection in a superconducting quantum circuit.
Quantum computing becomes viable when a quantum state can be protected from environment-induced error. If quantum bits (qubits) are sufficiently reliable, errors are sparse and quantum error correction (QEC) is capable of identifying and correcting them. Adding more qubits improves the preservation of states by guaranteeing that increasingly larger clusters of errors will not cause logical failure-a key requirement for large-scale systems. Using QEC to extend the qubit lifetime remains one of the outstanding experimental challenges in quantum computing. Here we report the protection of classical states from environmental bit-flip errors and demonstrate the suppression of these errors with increasing system size. We use a linear array of nine qubits, which is a natural step towards the two-dimensional surface code QEC scheme, and track errors as they occur by repeatedly performing projective quantum non-demolition parity measurements. Relative to a single physical qubit, we reduce the failure rate in retrieving an input state by a factor of 2.7 when using five of our nine qubits and by a factor of 8.5 when using all nine qubits after eight cycles. Additionally, we tomographically verify preservation of the non-classical Greenberger-Horne-Zeilinger state. The successful suppression of environment-induced errors will motivate further research into the many challenges associated with building a large-scale superconducting quantum computer.
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Kelly
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Barends
1] Department of Physics, University of California, Santa Barbara, California 93106, USA [2] Centre for Quantum Computation and Communication Technology, School of Physics, The University of Melbourne, Victoria 3010, Australia.
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Fowler
1] Department of Physics, University of California, Santa Barbara, California 93106, USA [2] Department of Materials, University of California, Santa Barbara, California 93106, USA.
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Megrant
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Jeffrey
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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White
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Sank
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Mutus
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Campbell
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Chen
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Chen
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Chiaro
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Dunsworth
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Hoi
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Neill
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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O'Malley
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Quintana
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Roushan
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Vainsencher
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Wenner
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Cleland
Department of Physics, University of California, Santa Barbara, California 93106, USA.
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Martinis