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Structure and Classification of Matrix Product Quantum Channels

Giorgio Stucchi*, J. Ignacio Cirac, Rahul Trivedi, and Georgios Styliaris†

  • *Contact author: giorgio.stucchi@mpq.mpg.de
  • †Contact author: georgios.styliaris@mpq.mpg.de
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Phys. Rev. Lett. 137, 120401 – Published 16 September, 2026

DOI: https://doi.org/10.1103/4216-bgrp

Abstract

We develop a framework for matrix product quantum channels, a one-dimensional tensor-network description of completely positive, trace-preserving maps. We focus on translation-invariant channels, generated by a single repeated tensor, that admit a local purification. We show that their purifying isometry can always be implemented by a constant-depth brickwork quantum circuit, implying that such channels generate only short-range correlations when applied on product states. In contrast to the unitary setting, where one-dimensional quantum cellular automata (in one-to-one correspondence with matrix product unitaries) carry a nontrivial index, we prove that all locally purified channels belong to a single phase, that is, they can be continuously deformed into one another. Then, we extend the framework to a broader class of translation-invariant channels capable of generating long-range entanglement and show that these remain deterministically implementable in constant depth using two rounds of measurements and feedforward.

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Outline

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Phys. Rev. Lett. 137, 120401– Published 16 September, 2026
  • Received 26 March 2026
  • Revised 6 July 2026
  • Accepted 21 August 2026
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