  We experimentally study the interference of dipole scattered light from two
optically levitated nanoparticles in vacuum, which present an environment free
of particle-substrate interactions. We illuminate the two trapped nanoparticles
with a linearly polarized probe beam orthogonal to the propagation of the
trapping laser beams. The scattered light from the nanoparticles are collected
by a high numerical aperture (NA) objective lens and imaged. The interference
fringes from the scattered vector light for the different dipole orientations
in image and Fourier space are observed. Especially, the interference fringes
of two scattered light fields with polarization vortex show the {\pi} shift of
the interference fringes between inside and outside the center region of the
two nanoparticles in the image space. As far as we know, this is the first
experimental observation of the interference of scattered vector light fields
from two dipoles in free space. This work also provides a simple and direct
method to determine the spatial scales between optically levitated
nanoparticles by the interference fringes.
