Non-reciprocal and artificial Λ-type systems in waveguide QED with parametrically modulated superconducting qubits

We present a non-local quantum system based on a waveguide QED architecture, comprising two spatially separated and largely detuned superconducting transmon qubits. By applying parametric frequency modulation to one of the qubits, we establish a tunable coherent channel between the two far-detuned qubits, thereby forming an Λ-type three-level system. We demonstrate that tuning the modulation amplitude enables the observation of spectral evolution from electromagnetically induced transparency (EIT) to Autler–Townes splitting (ATS). Furthermore, by exploiting the interplay between the non-local waveguide phase and system dissipation, the system achieves significant non-reciprocal microwave transmission and direction-selective photon emission. The scheme operates without external magnetic fields, offering an efficient pathway for realizing on-chip integrated quantum routers and isolators.