The ZX calculus is a language for surface code lattice surgery

Niel de Beaudrap1 and Dominic Horsman2

1Department of Computer Science, University of Oxford, Parks Road, Oxford, OX1 3QD
2Department of Physics, Durham University, South Road, Durham, DH1 1LE Department of Computer Science, University of Oxford, Parks Road, Oxford, OX1 3QD

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A leading choice of error correction for scalable quantum computing is the surface code with lattice surgery. The basic lattice surgery operations, the merging and splitting of logical qubits, act non-unitarily on the logical states and are not easily captured by standard circuit notation. This raises the question of how best to design, verify, and optimise protocols that use lattice surgery, in particular in architectures with complex resource management issues. In this paper we demonstrate that the operations of the ZX calculus --- a form of quantum diagrammatic reasoning based on bialgebras --- match exactly the operations of lattice surgery. Red and green ``spider'' nodes match rough and smooth merges and splits, and follow the axioms of a dagger special associative Frobenius algebra. Some lattice surgery operations require non-trivial correction operations, which are captured natively in the use of the ZX calculus in the form of ensembles of diagrams. We give a first taste of the power of the calculus as a language for lattice surgery by considering two operations (T gates and producing a CNOT) and show how ZX diagram re-write rules give lattice surgery procedures for these operations that are novel, efficient, and highly configurable.

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Cited by

[1] Niel de Beaudrap, Ross Duncan, Dominic Horsman, and Simon Perdrix, "Pauli Fusion: a Computational Model to Realise Quantum Transformations from ZX Terms", Electronic Proceedings in Theoretical Computer Science 318, 85 (2020).

[2] Michael Hanks, Marta P. Estarellas, William J. Munro, and Kae Nemoto, "Effective Compression of Quantum Braided Circuits Aided by ZX-Calculus", Physical Review X 10 4, 041030 (2020).

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[5] Joseph Collins and Ross Duncan, "Hopf-Frobenius Algebras and a Simpler Drinfeld Double", Electronic Proceedings in Theoretical Computer Science 318, 150 (2020).

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[7] Bob Coecke, Dominic Horsman, Aleks Kissinger, and Quanlong Wang, "Kindergarden quantum mechanics graduates ...or how I learned to stop gluing LEGO together and love the ZX-calculus", Theoretical Computer Science 897, 1 (2022).

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The above citations are from Crossref's cited-by service (last updated successfully 2023-06-07 10:01:02) and SAO/NASA ADS (last updated successfully 2023-06-07 10:01:03). The list may be incomplete as not all publishers provide suitable and complete citation data.