Quantum Circuit Noise Limits Depth

A new theoretical study, led by researchers Armando Angrisani and Yihui Quek at École Polytechnique Fédérale de Lausanne, Antonio Anna Mele at the Humboldt University of Berlin, and Daniel Stilck França at the University of Copenhagen, has revealed that noise significantly limits the practical depth of quantum circuits. Published in Nature Physics on April 2, 2026, the research indicates that in most noisy quantum circuits, only the last few operational steps truly matter, as noise gradually erases the influence of earlier steps. This implies that deep noisy circuits behave like much shallower ones, affecting their trainability and simulation on classical computers. The study clarifies the realistic capabilities of near-term quantum machines and suggests that future progress depends on better noise control or carefully engineered designs rather than simply increasing circuit layers. Contributors to the study also included Sorbonne University, University of Chicago, Fraunhofer Institute for Telecommunications, École normale supérieure de Lyon, and Massachusetts Institute of Technology.