Unidirectional rotation of circles driven by chiral active particles

The dynamics of two-dimensional rigid circles filled with chiral active particles are investigated by employing the overdamped Langevin dynamics simulations. Unidirectional rotation of rigid circles is observed, and the rotational angular velocity（ω） relies mainly on the length（l）, the number（nB）, and tilt angle（γ） of boards, and the angular velocity（ω）and area fraction（ρ） of chiral active particles. There are optimum values for these parameters at which the average angular velocity of circle reaches its maximum. The center-of-mass mean square displacement for circles drops by about two orders of magnitude for large angular velocity ω of chiral active particles with oscillations in the short-time regime. Our work demonstrates that nanofabricated objects with suitable designs immersed in a bath of chiral active particles can extract and rectify energy in a unidirectional motion.

Spatiotemporal rotational dynamics of laser-driven molecules

Molecular alignment and orientation by laser fields has attracted significant attention in recent years,mostly due to new capabilities to manipulate the molecular spatial arrangement.Molecules can now be efficiently prepared for ionization,structural imaging,orbital tomography,and more,enabling,for example,shooting of dynamic molecular movies.Furthermore,molecular alignment and orientation processes give rise to fundamental quantum and classical phenomena like quantum revivals,Anderson localization,and rotational echoes,just to mention a few.We review recent progress on the visualization,coherent control,and applications of the rich dynamics of molecular rotational wave packets driven by laser pulses of various intensities,durations,and polarizations.In particular,we focus on the molecular unidirectional rotation and its visualization,the orientation of chiral molecules,and the three-dimensional orientation of asymmetric-top molecules.Rotational echoes are discussed as an example of nontrivial dynamics and detection of prepared molecular states.