Towards Non-reciprocal Interactions between Degenerate Qubits via Spatio-temporal Modulation

Non-reciprocal interactions between quantum-coherent degrees of freedom are vital for constructing directional quantum networks and exploring non-Hermitian physics. However, few experimental realizations have been reported, particularly within degenerate quantum systems. We extend the simple spatio-temporal modulation method, developed in Ref. [1] to implement strongly amplitude- and phase-asymmetric coupling between degenerate harmonic oscillators, to a superconducting transmon-qubit chain. In this case, phase-staggered temporal modulation to qubit frequencies, instead of leading to isolation or gyration, leads to non-reciprocal excitation transfer or entanglement between two degenerate qubits. This work enables the implementation of controlled qubit-state evolution and non-reciprocal state exchange in coupled-qubit networks, paving the way for directional quantum information transmission and processing.

[1] Z. Tu, V. Workman, G. Bahl, A. J. Kollár, Realization of pure gyration in an on-chip superconducting microwave device, arXiv:2506.19912.