2025-08-05 カリフォルニア工科大学(Caltech)
＜関連情報＞
- https://www.caltech.edu/about/news/quantum-chaos-kicks-in-sooner-than-previously-thought
- https://www.science.org/doi/10.1126/science.adv8590
極低深度におけるランダムユニタリー Random unitaries in extremely low depth
Thomas Schuster, Jonas Haferkamp, and Hsin-Yuan Huang
Science Published:3 Jul 2025
DOI:https://doi.org/10.1126/science.adv8590
Editor’s summary
Understanding random processes in nature is important across a range of science and engineering fields. In quantum science, randomization is achieved by the generation of Haar unitary matrices. However, present protocols for the generation of random unitary operations is thought to take long evolution times and require deep circuits. By contrast, Schuster et al. found that local quantum circuits can form random unitaries in exponentially lower depths rather than in the polynomial depths seen in classical dynamics (see the Perspective by Yamamoto and Wada). Such a speedup will be important for benchmarking quantum technologies and probing complex quantum dynamics. —Ian S. Osborne
Abstract
Random unitaries are central to quantum technologies and the study of complex quantum many-body physics. However, existing protocols for generating random unitaries require long evolution times and deep circuits. In this work, we prove that local quantum circuits can form random unitaries in extremely low depth on any geometry. These shallow circuits have low complexity and create only short-range correlations, yet are indistinguishable from random unitaries with exponential complexity. This finding contrasts sharply with classical systems, in which a long evolution time is required to appear random. Our results have widespread applications across quantum science, from device benchmarking to quantum advantages. Moreover, they reveal that fundamental physical properties—including evolution time, causal structure, and phases of matter—are provably hard to learn.
