Universal spreading of conditional mutual information in noisy random circuits

Physical Review Letters (2024)

 

Scientists explore how conditional mutual information (CMI) — a measure of the information shared between parts of a system, given a third part — evolves in open quantum systems affected by noise. The researchers focus on random quantum circuits, which are systems where interactions and operations are applied in random patterns, mixed with local noise at every step.

In circuits without noise, CMI spreads predictably and linearly, staying within a “light cone.” When noise is introduced, the spread of CMI accelerates beyond the light cone and diverges at a critical depth that scales inversely with the noise level.

The researchers developed a mathematical tool called a coarse-graining method to model how CMI evolves in these noisy systems. Their theoretical results align with their numerical simulations. They also identified a general scaling law that describes the behavior of CMI spreading across various noisy quantum systems.

Understanding how information spreads in noisy quantum systems is crucial for quantum error correction. It’s also important for something called scrambling dynamics, which describe how information becomes distributed and locally inaccessible.

The paper’s authors are Su-un Lee, Changhun Oh, Yat Wong, Senrui Chen and Liang Jiang, conducting their work at the University of Chicago and the Korea Advanced Institute of Science and Technology.