  Environment-induced localization transitions (LT) occur when a small quantum
system interacts with a bath of harmonic oscillators. At equilibrium, LTs are
accompanied by an entropy change, signaling the loss of coherence. Despite
extensive efforts, equilibrium LTs have yet to be observed. Here, we
demonstrate that ongoing experiments on double quantum dots that measure
entropy using a nearby quantum point contact (QPC) realize the celebrated
spin-boson model and allow to measure the entropy change of its LT. We find a
Kosterlitz-Thouless flow diagram, leading to a universal jump in the spin-bath
interaction, reflected in a discontinuity in the zero temperature QPC
conductance.
