Angle- and field-tunable unidirectional zero reflection in an asymmetric single-defect atomic lattice.

Based on spatial symmetry breaking, we propose a tunable unidirectional zero-reflection scheme in a one-dimensional single-defect atomic lattice. Reflection suppression stems from destructive interference between the direct-reflection and multiple-scattering components, whose amplitudes and phases are co-modulated by coherent atomic response, Bragg scattering, and structural asymmetry. The system supports both broadband and narrowband asymmetric-reflection regions, each containing a unidirectional zero-reflection point, with the minimum reflectivity reaching below 10-6 in one incident direction while remaining above 0.93 in the reverse direction. External coherent fields tune the UZR frequency, and the vacant-region length modulates phase and scattering amplitudes for zero-reflection at discrete incident angles. Boasting robustness against atom number density fluctuations, this work provides an intuitive theoretical framework for directional scattering, promising tunable optical switches, low-back-reflection photonic structures, and asymmetric light-control devices.