  Active matter such as swarming bacteria and motile colloids exhibits exotic
properties different from conventional equilibrium materials. Among these
properties, the enhanced diffusion of tracer particles is generally deemed as a
hallmark of active matter. Here, rather than spherical tracers, we investigate
the diffusion of isolated ellipsoids in quasi-two-dimensional bacterial bath.
Our study reveals a nonlinear enhancement of both translational and rotational
diffusions. More importantly, we uncover an anomalous coupling between
translation and rotation that is strictly prohibited in the classic Brownian
diffusion. Combining experiments with theoretical modeling, we show that such
an anomaly arises from generic stretching flows induced by swimming bacteria.
Our work illustrates a universal organizing principle of active matter and
sheds new light on fundamental transport processes in microbiological systems.
