Preparing encoded logical states is the first step in a fault-tolerant quantum computation. Standard approaches based on concatenation or repeated measurement incur a significant time overhead. The Raussendorf-Bravyi-Harrington cluster state [Raussendorf et al., 2005] offers an alternative: a single-shot preparation of encoded states of the surface code, by means of a constant depth quantum circuit, followed by a single round of measurement and classical feedforward [Bravyi et al., 2020]. In this work we generalize this approach and prove that single-shot logical state preparation can be achieved for arbitrary quantum LDPC codes. Our proof relies on a minimum-weight decoder and is based on a generalization of Gottesman’s clustering-of-errors argument [Gottesman, 2014]. As an application, we also prove single-shot preparation of the encoded GHZ state in arbitrary quantum LDPC codes. This shows that adaptive noisy constant depth quantum circuits are capable of generating generic robust long-range entanglement.
@InProceedings{bergamaschi_et_al:LIPIcs.ITCS.2025.16, author = {Bergamaschi, Thiago and Liu, Yunchao}, title = {{On Fault Tolerant Single-Shot Logical State Preparation and Robust Long-Range Entanglement}}, booktitle = {16th Innovations in Theoretical Computer Science Conference (ITCS 2025)}, pages = {16:1--16:9}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-361-4}, ISSN = {1868-8969}, year = {2025}, volume = {325}, editor = {Meka, Raghu}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2025.16}, URN = {urn:nbn:de:0030-drops-226444}, doi = {10.4230/LIPIcs.ITCS.2025.16}, annote = {Keywords: Quantum error correction, fault tolerance, single-shot error correction, logical state preparation} }
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