Quantum nonreciprocity from qubits coupled by Dzyaloshinskii–Moriya interaction

One-dimensional waveguides provide a structured, bidirectional environment that cleanly separates forward/backward modes and the coherent/incoherent parts of fluorescence—an ideal platform for probing directionality in transport and quantum features. We use this setting to show that a complex Dzyaloshinskii–Moriya interaction (DMI) in an otherwise achiral waveguide induces not only nonreciprocal transmission but also direction-dependent quantum features: steady-state quantum entanglement and photon correlations. We model two qubits coupled to a one-dimensional waveguide driven by a coherent field. We show that an engineered complex DMI enables strong nonreciprocity in an otherwise reciprocal system, with tunable behavior governed by driving strength, detuning, and phase of the DMI. At phase-matched separations, the two-qubit system can end up in a pure steady state as certain decohering channels do not participate. The pure state can generate perfect reciprocal transparency. Away from these points, tuning the phases programs strong nonreciprocal entanglement. We further demonstrate the generation of superbunching light, with superbunching strongly dependent on phase and coupling strength, appearing in transmission for no extra DMI and shifting to reflection for finite DMI. Our results position complex DMI as a versatile resource enabling isolators, routers, and superbunching light sources without requiring chiral waveguides.