Nanoscale feedback control of six degrees of freedom of a near-sphere

We demonstrate feedback cooling of all the angular motions of a near-spherical neutral nanoparticle with all the translational motions feedback-cooled to near the ground state. The occupation numbers of the three translational motions are $6 \pm 1$, $6 \pm 1$, and $0.69 \pm 0.18$. A tight, anisotropic optical confinement allows us to clearly observe three angular oscillations and to identify the ratio of two radii to the longest radius with a precision of $\unit[0.09]{\%}$. We develop a thermometry for three angular oscillations and realize feedback cooling of them to temperatures of lower than $\unit[0.03]{K}$ by electrically controlling the electric dipole moment of the nanoparticle. Our work not only paves the way to precisely characterize trapped nanoparticles, but also forms the basis of utilizing them for acceleration sensing and for exploring quantum mechanical behaviors with both their translational and rotational degrees of freedom.