Tianchu's hierarchical equations of motion paper accepted in Physical Review Letters

Congratulations to Tianchu for his paper “Hidden gauge freedom in complex-pole hierarchical equations of motion,” just accepted in Physical Review Letters! Complex-pole hierarchical equations of motion (HEOM) enable numerically exact simulations of open quantum systems but suffer from numerical instabilities. Tianchu discovered a previously unknown gauge freedom: a continuous family of equivalent equations, all describing the same environment, whose numerical stability varies dramatically. Optimizing this gauge yields GO–HEOM, which removes these instabilities and extends numerically exact simulations to coupling strengths that were previously out of reach, including through the delocalized-to-localized quantum phase transition in sub-Ohmic environments.