Why two coupled quantum oscillators refuse to reach thermal equilibrium

Two strongly coupled quantum oscillators with independent heat baths at the same temperature should, by all standard expectations, settle into a simple Boltzmann distribution. Instead, when the oscillators lose energy to their baths at different rates, a persistent flux of excitations driven by quantum coherences between nearly identical energy levels locks the system into a non-thermal steady state. The finding challenges routine use of the secular approximation in open quantum systems and suggests measurable signatures in trapped-ion or circuit-QED platforms.