Fano-qubits for quantum devices with enhanced isolation and bandwidth

Quantum devices often suffer from reflections and noise during readout, a problem traditionally addressed by magneto-optical isolators and circulators. However, these solutions are hindered by limited bandwidth, low tunability, high losses, and incompatibility with planar technologies like circuit QED. To overcome these challenges, we introduce an approach to quantum non-reciprocity, leveraging the inherent nonlinearity of qubits and spatial symmetry disruption. Our method transforms a circuit with Lorentz-type qubits into one with Fano-type qubits, which exhibit an asymmetric spectral response. This transformation leads to a significant enhancement in isolation (up to 40 dB) and a doubling of spectral bandwidth (up to 200 MHz). We base our analysis on realistic circuit parameters and substantiate it with existing experimental results and comprehensive quantum simulations. Our research paves the way for creating compact, high-performance, planar-compatible non-reciprocal quantum devices. These devices could revolutionize quantum computing, communication, and sensing by offering improved noise protection and broader bandwidth.