Inverted Sedimentation of Active Particles in Unbiased ac Fields

Gaining control over the motion of active particles is crucial for applications ranging from targeted cargo delivery to nanomedicine. While much progress has been made recently based on external forces, flows or gradients in concentration light intensity, which all have a well-defined direction bias, little known about how steer situations where no permanent bias can be realized. Here, we show that ac fields with vanishing time average provide an alternative route steering particles. We exemplify this inertial gravitational field, observing substantial fraction them persistently travels upward upon switching resulting inverted sedimentation profile at top wall confining container. Our results offer generic principle could used future motion, direct collective behaviors and purify mixtures.