Work

Quantum memory precludes mixed-unitary dynamics

Year: 2026

Type: article

Abstract: Unital quantum channels, defined by their property of leaving the maximally mixed state invariant, form an important class of quantum operations. A distinguished subset of these channels can be represented as a probabilistic mixture of unitary evolutions. Characterizing channels that do not admit such a decomposition is in general a hard problem with significant implications for noise mitigation in quantum technologies and for fundamental problems in quantum information theory. Here, we establish a link between mixed unitarity of unital channels and the (quantum) nature of the memory effects in non-Markovian dynamics. Translating the problem into the language of process tensors, this connection yields a hierarchy of semidefinite programs that provides numerically efficient witnesses for non-mixed-unitary behavior, outperforming existing criteria. We demonstrate the power of this approach through illustrative examples of unital channels in dimensions 3 and 4, and show how the method can detect non-mixed-unitary behavior based on incomplete channel tomography.

Source: Physical Review Research

DOI: 10.1103/dn6t-y9ky

Authors: Charlotte Bäcker, Konstantin Beyer, Walter T. Strunz

Institutions: Technische Universität Dresden, Stevens Institute of Technology

Language: English

Topic: Quantum Information and Cryptography

Subfield: Artificial Intelligence

Field: Computer Science

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $2,625

Funders: National Science Foundation, National Aeronautics and Space Administration, Alfred P. Sloan Foundation