  The motion control of a levitated nanoparticle plays a central role in
optical levitation for fundamental studies and practical applications. Here, we
presented a digital parametric feedback cooling based on switching between two
trapping laser intensity levels with square wave modulations. The effects of
modulation depth and modulation signal phase on the cooling result were
investigated in detail. With such a digital parametric feedback method, the
centre-of-mass temperature of all three motional degrees of freedom can be
cooled to dozens of milli-Kelvin, which paved the way to fully control the
motion of the levitated nanoparticle with a programmable digital process for
wild applications.
