  Optical tweezers, which are powerful tools for trapping and manipulating
particles, have been widely used in many areas. However, their potential wells
are typically symmetrical, which limit their capability of optical trapping and
manipulation. Herein, we report an approach for dynamically creating
asymmetrical potential wells, by employing variable phase gradient profiles
generated by holograms. Its depth, stiffness and location of potential wells
can be dynamically controlled. Moreover, the controllable transport of
nanoparticle is experimentally demonstrated, which reveals that it exhibits
excellent manipulation performance. Importantly, its motion path, step distance
and velocity can be easily manipulated by changing its holograms, which is
highly desirable in controllable transport of nanoparticles. This study offers
a new tool for optical manipulation, which could largely expand the capability
of conventional optical tweezers.
