b. Manipulation of Single Quantum Dots to Nanometer Precision
Our control method scales favorably for extremely small particles. With laser tweezers it is very hard to trap nanometer size particles because the trapping forces scale with particle volume, for quantum dots the trapping forces are very close to thermal kT forces. Even if a trap is created it is not specific -- it can suck in multiple quantum dots.
By improving our optics, increasing the fluid viscosity, pausing the control when the quantum dot blinks off and then reacquiring it when it blinks back on, and by adding an additional feedback loop to autofocus in the vertical direction, we have been able to control, to steer and trap, a single quantum dot to nanometer precision for over an hour.