example, a dense bacterial suspension is driven out of equilibrium by the autonomous motion of self-propelled bacteria suspended therein[@yeomans; @frey; @kokot; @Li]. The alignment between bacteria shapes the active turbulence patterns of collective swimming into vortices of similar size[@wioland1; @wioland2; @beppu; @hamby; @clement; @nishiguchi2]. However, this vortical order decays over distance, making it a long-standing issue for the development of ordered dynamics at larger scales. Hence, a growing attention is paid to novel strategies to control active turbulence with simple geometric design.

![**Chiral bacterial vortex.** (a) Experimental setup: a dense bacterial suspension confined in hydrophilic-treated PDMS microwells and sealed under oil/water interface stabilized with a surfactant. (b) Ensemble of chiral bacterial vortices, in microwells with radius (top row) and (bottom row). Color map codes for the direction of the velocity field. Scale bar, . Schematic illustration of a bacterial vortex in a single microwell. “+” defines the positive sign of CCW rotation. CCW and CW occurrences are displayed in blue and red arrows, respectively.[]{data-label="fig1"}](figure1_9.jpg)

Chirality, i.e. the non-equivalence of opposite handedness, is ubiquitous across scales[@bahr], and is commonly involved in active systems[@glotzer; @lowen; @levis; @lenz], either biological, such as bacteria[@whitesides; @haoran; @howard; @petroff], cytoskeletons and molecular motors[@tee; @frey2; @kim], or 