  We analyze theoretically the motional quantum dynamics of a levitated
dielectric sphere interacting with the quantum electromagnetic field beyond the
point-dipole approximation. To this end, we derive a Hamiltonian describing the
fundamental coupling between photons and center-of-mass phonons, including
Stokes and anti-Stokes processes, and the coupling rates for a dielectric
sphere of arbitrary refractive index and size. We then derive the laser recoil
heating rates and the information radiation patterns (the angular distribution
of the scattered light that carries information about the center-of-mass
motion) and show how to evaluate them efficiently in the presence of a focused
laser beam, in either a running- or a standing-wave configuration. This
information is crucial to implement active feedback cooling of optically
levitated dielectric spheres beyond the point-dipole approximation. Our results
predict several experimentally feasible configurations and parameter regimes
where optical detection and active feedback can simultaneously cool to the
ground state the three-dimensional center-of-mass motion of dielectric spheres
in the micrometer regime. Scaling up the mass of the dielectric particles that
can be cooled to the center-of-mass ground state is relevant not only for
testing quantum mechanics at large scales but also for current experimental
efforts that search for new physics (e.g., dark matter) using optically
levitated sensors.
