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Gupta RS, Sundaresan N, Alexander T, Wood CJ, Merkel ST, Healy MB, Hillenbrand M, Jochym-O'Connor T, Wootton JR, Yoder TJ, Cross AW, Takita M, Brown BJ. Encoding a magic state with beyond break-even fidelity. Nature 2024; 625:259-263. [PMID: 38200302 PMCID: PMC10781628 DOI: 10.1038/s41586-023-06846-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Accepted: 11/07/2023] [Indexed: 01/12/2024]
Abstract
To run large-scale algorithms on a quantum computer, error-correcting codes must be able to perform a fundamental set of operations, called logic gates, while isolating the encoded information from noise1-8. We can complete a universal set of logic gates by producing special resources called magic states9-11. It is therefore important to produce high-fidelity magic states to conduct algorithms while introducing a minimal amount of noise to the computation. Here we propose and implement a scheme to prepare a magic state on a superconducting qubit array using error correction. We find that our scheme produces better magic states than those that can be prepared using the individual qubits of the device. This demonstrates a fundamental principle of fault-tolerant quantum computing12, namely, that we can use error correction to improve the quality of logic gates with noisy qubits. Moreover, we show that the yield of magic states can be increased using adaptive circuits, in which the circuit elements are changed depending on the outcome of mid-circuit measurements. This demonstrates an essential capability needed for many error-correction subroutines. We believe that our prototype will be invaluable in the future as it can reduce the number of physical qubits needed to produce high-fidelity magic states in large-scale quantum-computing architectures.
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Affiliation(s)
- Riddhi S Gupta
- IBM Quantum, T. J. Watson Research Center, Yorktown Heights, NY, USA
- IBM Quantum, Almaden Research Center, San Jose, CA, USA
| | | | - Thomas Alexander
- IBM Quantum, T. J. Watson Research Center, Yorktown Heights, NY, USA
| | | | - Seth T Merkel
- IBM Quantum, T. J. Watson Research Center, Yorktown Heights, NY, USA
| | - Michael B Healy
- IBM Quantum, T. J. Watson Research Center, Yorktown Heights, NY, USA
| | | | - Tomas Jochym-O'Connor
- IBM Quantum, T. J. Watson Research Center, Yorktown Heights, NY, USA
- IBM Quantum, Almaden Research Center, San Jose, CA, USA
| | | | - Theodore J Yoder
- IBM Quantum, T. J. Watson Research Center, Yorktown Heights, NY, USA
| | - Andrew W Cross
- IBM Quantum, T. J. Watson Research Center, Yorktown Heights, NY, USA
| | - Maika Takita
- IBM Quantum, T. J. Watson Research Center, Yorktown Heights, NY, USA
| | - Benjamin J Brown
- IBM Quantum, T. J. Watson Research Center, Yorktown Heights, NY, USA.
- IBM Denmark, Brøndby, Denmark.
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Abstract
Quantum error correction and fault tolerance make it possible to perform quantum computations in the presence of imprecision and imperfections of realistic devices. An important question is to find the noise rate at which errors can be arbitrarily suppressed. By concatenating the 7-qubit Steane and 15-qubit Reed-Muller codes, the 105-qubit code enables a universal set of fault-tolerant gates despite not all of them being transversal. Importantly, the cnot gate remains transversal in both codes, and as such has increased error protection relative to the other single qubit logical gates. We show that while the level-1 pseudothreshold for the concatenated scheme is limited by the logical Hadamard gate, the error suppression of the logical cnot gates allows for the asymptotic threshold to increase by orders of magnitude at higher levels. We establish a lower bound of 1.28×10^{-3} for the asymptotic threshold of this code, which is competitive with known concatenated models and does not rely on ancillary magic state preparation for universal computation.
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Affiliation(s)
- Christopher Chamberland
- Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
| | - Tomas Jochym-O'Connor
- Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
| | - Raymond Laflamme
- Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
- Perimeter Institute, Waterloo, Ontario N2L 2Y5, Canada
- Canadian Institute For Advanced Research, Toronto, Ontario M5G 1Z8, Canada
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Jochym-O'Connor T, Laflamme R. Using concatenated quantum codes for universal fault-tolerant quantum gates. Phys Rev Lett 2014; 112:010505. [PMID: 24483879 DOI: 10.1103/physrevlett.112.010505] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Indexed: 06/03/2023]
Abstract
We propose a method for universal fault-tolerant quantum computation using concatenated quantum error correcting codes. The concatenation scheme exploits the transversal properties of two different codes, combining them to provide a means to protect against low-weight arbitrary errors. We give the required properties of the error correcting codes to ensure universal fault tolerance and discuss a particular example using the 7-qubit Steane and 15-qubit Reed-Muller codes. Namely, other than computational basis state preparation as required by the DiVincenzo criteria, our scheme requires no special ancillary state preparation to achieve universality, as opposed to schemes such as magic state distillation. We believe that optimizing the codes used in such a scheme could provide a useful alternative to state distillation schemes that exhibit high overhead costs.
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Affiliation(s)
- Tomas Jochym-O'Connor
- Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada and Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
| | - Raymond Laflamme
- Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada and Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada and Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, Ontario N2L 2Y5, Canada
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Jochym-O'Connor T, Kribs DW, Laflamme R, Plosker S. Private quantum subsystems. Phys Rev Lett 2013; 111:030502. [PMID: 23909301 DOI: 10.1103/physrevlett.111.030502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Revised: 01/23/2013] [Indexed: 06/02/2023]
Abstract
We investigate the most general notion of a private quantum code, which involves the encoding of qubits into quantum subsystems and subspaces. We contribute to the structure theory for private quantum codes by deriving testable conditions for private quantum subsystems in terms of Kraus operators for channels, establishing an analogue of the Knill-Laflamme conditions in this setting. For a large class of naturally arising quantum channels, we show that private subsystems can exist even in the absence of private subspaces. In doing so, we also discover the first examples of private subsystems that are not complemented by operator quantum error correcting codes, implying that the complementarity of private codes and quantum error correcting codes fails for the general notion of private quantum subsystems.
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Affiliation(s)
- Tomas Jochym-O'Connor
- Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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