,
Eric Samperton
Creative Commons Attribution 4.0 International license
We show that for any fixed (2+1)-dimensional TQFT over ℂ of either Turaev-Viro-Barrett-Westbury or Reshetikhin-Turaev type, the problem of (exactly) computing its invariants on closed 3-manifolds is either solvable in polynomial time, or else it is #𝖯-hard to (exactly) contract certain tensors that are built from the TQFT’s fusion category. Our proof is an application of a dichotomy result of Cai and Chen [J. ACM, 2017] concerning weighted constraint satisfaction problems over ℂ. We leave for future work the issue of reinterpreting the conditions of Cai and Chen that distinguish between the two cases (i.e. #𝖯-hard tensor contractions vs. polynomial time invariants) in terms of fusion categories. We expect that with more effort, our reduction can be improved so that one gets a dichotomy directly for TQFTs' invariants of 3-manifolds rather than more general tensors built from TQFTs' fusion categories.
@InProceedings{bridges_et_al:LIPIcs.TQC.2025.5,
author = {Bridges, Nicolas and Samperton, Eric},
title = {{Towards a Complexity-Theoretic Dichotomy for TQFT Invariants}},
booktitle = {20th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2025)},
pages = {5:1--5:21},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-392-8},
ISSN = {1868-8969},
year = {2025},
volume = {350},
editor = {Fefferman, Bill},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2025.5},
URN = {urn:nbn:de:0030-drops-240548},
doi = {10.4230/LIPIcs.TQC.2025.5},
annote = {Keywords: Complexity, topological quantum field theory, dichotomy theorems, constraint satisfaction problems, tensor categories}
}