Local spin manipulation of quantized atomic currents.

Spin is a fundamental quantum property of matter, and lifting its degeneracy lies at the heart of subtle transport phenomena and future schemes for quantum information processing. Here, we implement a microscopic spin filter for cold fermionic atoms in a quantum point contact (QPC) which allows us to create fully spin-polarized currents while retaining conductance quantization. Key to our scheme is a near-resonant optical tweezer which induces an effective Zeeman shift inside the QPC while its local character limits dissipation. We measure global effects of non-Hermitian evolution and interactions on the scale of the Fermi wavelength. Our work paves the way to studying hybrid mesoscopic structures combining spin-splitting and superfluidity far from equilibrium.