Tunable Directional Photon Scattering from a Pair of Superconducting Qubits*

Nonreciprocal integrated devices provide flexibility and scalability for a wide range of on-chip applications, such as integrated photonics, quantum information processing, and nonlinear optics. We demonstrate tunable directional scattering of microwave radiation with just two transmon qubits coupled to a transmission line. When the qubits are tuned in resonance with each other such that the effective distance between them is equal to a quarter of the qubit excitation wavelength, we periodically modulate their transition frequency. The resulting interference between the two qubits enables directional forward or backward scattering of Stokes and anti-Stokes components depending on the relative phase between the local modulation tones in analogy to the optomechanical Kerker effect. Such a nonreciprocal device is compatible with modern superconducting qubit technology and can be used to route microwave radiation for the realization of chiral networks.