Topic: decoherence

Gate-set shadows extend randomized benchmarking toward practical noise tomography. On a 36-qubit superconducting processor, a single randomized-circuit experiment reconstructs local noise marginals and identifies correlated errors and cross-talk. Error-generator decompositions separate coherent, stochastic and correlated components, revealing patterns beyond physical nearest neighbours. Comparing these rates with standard mechanisms such as detuning, over-rotation and decoherence quantifies unexplained noise and suggests that familiar models can miss important cross-talk.

This lecture introduces decoherence through simple models of quantum systems exposed to environmental disturbances. It explains how electric or magnetic noise degrades superposition, how the effect is measured and how it can be reduced. The discussion relates these issues to the DiVincenzo requirements for quantum computers and compares major experimental platforms.