Tailored Dissipation for Directional Transport in Plasmonic Ratchets

Ratchets provide directed transport without global biased forces via parity-breaking combinations of nonequilibrium driving with dissipation or nonlinear dynamics. They play a central role down to the quantum level in molecular motors, colloidal particles, microbiological processes, semiconductor devices, optical lattices, and photonic structures, where nonequilibrium is usually achieved by dynamic potentials or couplings. Here, we address the question of whether transport can be achieved by only using time-dependent dissipation while keeping all potentials and couplings static. In this experiment-theory collaboration, we construct such non-Hermitian ratchets that solely rely on time- and space-periodic dissipation. Notably, the rectified transport increases with larger local dissipation. Floquet theory uncovers low-loss directional transport at suitable driving frequencies, which is linked to linear quasienergy bands. These regions are separated from nonresonant behavior by sharp transitions with characteristic exceptional points in the spectrum. A plasmonic Floquet-dissipative ratchet is studied experimentally by using real- and Fourier-space leakage radiation microscopy.