FTT Three-Mode Model Maps Non-Equilibrium Condensate Transition in Driven Superconducting Circuits

The preprint introduces an FTT three-mode Hamiltonian that explicitly tracks intermode coupling and bath-induced decay rates absent from standard single-mode Lindblad treatments. Periodic flux modulation applied to the fluxonium reveals occupation-transfer pathways that route population through auxiliary transmons before environmental release, producing the observed condensate-like buildup.

Increasing intrinsic loss on the auxiliary modes selectively engages additional dissipative channels, allowing controlled depletion of the target mode. This mechanism offers a design handle for engineering non-equilibrium recovery in circuit QED without relying solely on external drives.

Related experiments on driven-dissipative transmon arrays (Ma et al., PRX 2023) and fluxonium coherence under flux modulation (Nguyen et al., PRX Quantum 2022) already hint at similar intermode effects, yet lack the three-mode resolution needed to predict selective pathways. The FTT model therefore bridges a gap between abstract open-system theory and concrete circuit parameters.

Hardware validation on existing FTT devices within the next two years would test whether the predicted condensate-to-BEC crossover survives fabrication disorder and measurement back-action.