Dispersive Non-reciprocity between a Qubit and a Cavity*

Non-reciprocity is a valuable and unique property for building interesting and complex quantum systems. Previous study of non-reciprocity focuses on non-Hermitian Hamiltonian models for both linear and cascaded nonlinear systems, both of which study non-reciprocity of resonant excitation exchange. Quantum interactions between far-detuned modes are central to QIP, most prominently the reciprocal dispersive interaction. Here, we explore non-reciprocity between off-resonant quantum modes by presenting an experimental study of a non-reciprocal dispersive-type interaction between a transmon qubit and a superconducting cavity, arising from dissipative intermediary modes with broken time reversal symmetry. We characterize the qubit-cavity dynamics, including asymmetric frequency pulls and photon shot-noise dephasing, under varying degrees of non-reciprocity. Importantly, we show that the qubit-cavity dynamics can be well described for a wide parameter regime by a simple non-reciprocal master-equation model, which avoids the challenge of understanding the highly complex dynamics of the intermediary system. Our result provides an example of quantum non-reciprocal phenomena beyond the typical non-Hermitian Hamiltonian and cascaded system models.