Spatial superposition of a levitated nanoparticle larger than its size
In plain words
A glass bead about a hundred nanometers across can be held by laser light and cooled to its lowest quantum state of motion. The next step is a superposition of two places farther apart than the bead's own size, confirmed by interference.
Precise statement
For an optically or magnetically levitated dielectric particle of mass about $1e-15 \text{ to } 1e-14\,\mathrm{g}$ (radius $r \sim 5e-6 \text{ to } 1e-5\,\mathrm{cm}$) prepared near its motional ground state, create a coherent spatial superposition or wave packet with coherence length exceeding $r$, and verify coherence by interference fringes or Wigner-function negativity, since position variance alone does not distinguish coherent from incoherent spreading.
What would settle it
Release-and-recapture or inverted-potential interferometry showing center-of-mass interference fringes from a separation larger than r.
Status in the literature
Unverified note
In 2024 a ground-state-cooled nanoparticle's coherence length was increased more than threefold (arXiv:2408.01264) and a pre-cooled nanoparticle's motional state was expanded beyond its size (arXiv:2408.09596); no interference fringes at separations above the particle size were found in the literature checked.