The surface code with a twist

Theodore J. Yoder1 and Isaac H. Kim2

1Department of Physics, Massachusetts Institute of Technology
2IBM, Thomas J. Watson Research Center

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The surface code is one of the most successful approaches to topological quantum error-correction. It boasts the smallest known syndrome extraction circuits and correspondingly largest thresholds. Defect-based logical encodings of a new variety called twists have made it possible to implement the full Clifford group without state distillation. Here we investigate a patch-based encoding involving a modified twist. In our modified formulation, the resulting codes, called triangle codes for the shape of their planar layout, have only weight-four checks and relatively simple syndrome extraction circuits that maintain a high, near surface-code-level threshold. They also use 25% fewer physical qubits per logical qubit than the surface code. Moreover, benefiting from the twist, we can implement all Clifford gates by lattice surgery without the need for state distillation. By a surgical transformation to the surface code, we also develop a scheme of doing all Clifford gates on surface code patches in an atypical planar layout, though with less qubit efficiency than the triangle code. Finally, we remark that logical qubits encoded in triangle codes are naturally amenable to logical tomography, and the smallest triangle code can demonstrate high-pseudothreshold fault-tolerance to depolarizing noise using just 13 physical qubits.


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[2] Daniel Litinski, Felix von Oppen, "Braiding by Majorana tracking and long-range CNOT gates with color codes", Physical Review B 96, 205413 (2017).

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[4] Muyuan Li, Mauricio Gutiérrez, Stanley E. David, Alonzo Hernandez, Kenneth R. Brown, "Fault tolerance with bare ancillary qubits for a [[7,1,3]] code", Physical Review A 96, 032341 (2017).

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[6] Benjamin J. Brown, Katharina Laubscher, Markus S. Kesselring, James R. Wootton, "Poking Holes and Cutting Corners to Achieve Clifford Gates with the Surface Code", Physical Review X 7, 021029 (2017).

(The above data is from Crossref's cited-by service. Unfortunately not all publishers provide suitable and complete citation data so that some citing works or bibliographic details may be missing.)