Chiral cavity control of flat band Josephson Diode

Flat band systems have opened opportunities to access on-demand unconventional phenomena. Here, we demonstrate chiral cavity control of Josephson diodes at microwave frequencies. We show chirality-controlled diode response in gate-defined twisted bilayer graphene Josephson junctions (JJs), where cavity-induced time-reversal symmetry breaking, analogous to the Haldane model, enables a topological diode tunable by mode chirality and coupling strength. Focusing on SNS JJs, we show that long-wavelength microwaves break time-reversal symmetry in both superconducting and weak-link regions, extending control beyond spontaneously broken phases and enabling diode response unique to non-trivial flat bands. We find that the interplay of phase accumulation and non-trivial transmission across the junction leads to large diode efficiencies, nearly 30%. We further demonstrate chiral mode controlled 0-π transitions, enabling on-demand 0-π qubits.