Diamagnetically levitated pico-femtoliter volume droplets and/or particles can be used to study interactions between them and with environment. Force can be applied to the droplets/particles via magnetic, electric and gravitational fields with up to femto Newton accuracy, and potential energy can be controlled with up to 0.2 zepto J (0.05 kT) precision, thus providing experimental tools for fundamental studies.

The force acting on a levitating droplet/particle can be calibrated by using gravity as in the Millikan experiment. It is convenient to tilt the chip, i.e. to use "magnetic incline". We have used this approach in article to achive femtonewton resolution in force. However, this resolution can be improved by several orders of magnitude. Consider typical, 3 micron in diameter droplet. It has volume about 15 femtoliter and weight 150 femtonewtons. By controlling tilt angle with resolution of 0.1 millirad, it is feasible to calibrate force acting on the droplet with resolution 15 attonewtons. Typically droplet(s) are captured in a potential well. Tilt means droplet shift in this well. The "force constant" in such well in the direction parallel to the slit between the magnets can be as small as 10 attonewton/micron. With video system (microscope + camera) resolution of 0.1micron this provides possibility to control force with attonewton resolution. Of course, with such small value of force constant the amplitude of brownian motion (see next movie) can reach 10 micron. However, large enough statistic provides possibility for accurate measurements (see article for more details).

The levitated droplets captured in a magnetic "potential well" experience brownian motion. The left figure shows 3 snapshots of the pair of droplets about 8 microns in diameter captured in a potential well. The right figure shows displacement of the centre of mass and the distance between the droplets as a function of time. Note that the center of mass position oscillates stronger than the distance between droplets. This indicates strong bound state of the pair (see also video ).

This video shows brownian motion of the seven levitated droplets with diameters starting from 4 microns in a potential well.

This video shows motion of the levitated charged droplet. Droplet slides down on "magnetic incline" and is dragged up by the electric field applied between electrodes (red).