  Magneto-optical isolators and circulators have been widely used to safeguard
quantum devices from reflections and noise in the readout stage. However, these
devices have limited bandwidth, low tunability, are bulky, and suffer from high
losses, making them incompatible with planar technologies such as circuit QED.
To address these limitations, we propose a new approach to quantum
non-reciprocity that utilizes the intrinsic nonlinearity of qubits and broken
spatial symmetry. We show that a circuit containing Lorentz-type qubits can be
transformed into Fano-type qubits with an asymmetric spectral response,
resulting in a significant improvement in isolation (up to 40 dB) and a twofold
increase in spectral bandwidth (up to 200 MHz). Our analysis is based on
realistic circuit parameters, validated by existing experimental results, and
supported by rigorous quantum simulations. This approach could enable the
development of compact, high-performance, and planar-compatible non-reciprocal
quantum devices with potential applications in quantum computing,
communication, and sensing.
