Matter-wave interference with particles above one million atomic mass units
In plain words
The heaviest particles shown to interfere in a way classical physics cannot mimic weigh about 170,000 atomic mass units. Reaching a million or more, the mass of a small virus, requires slower beams and longer coherence.
Precise statement
Demonstrate near-field (Talbot-Lau) or far-field interference of neutral particles of mass $m \ge 1e6\,\mathrm{u}$ ($1.7e-18\,\mathrm{g}$) whose visibility versus grating power follows the quantum prediction and excludes the classical moire-shadow prediction at stated confidence, and report $\mu$. The 2025 analysis indicates metal clusters need velocities near $2.5e3\,\mathrm{cm}/\mathrm{s}$ in a $1e2\,\mathrm{cm}$ scale interferometer.
What would settle it
A Talbot-Lau or vertical interferometer run with MDa clusters, nanoparticles or biomolecules in which quantum and classical predictions differ and the data follow the quantum one.
Status in the literature
Unverified note
In 2025 sodium clusters of 0.4 to 1 MDa gave high-visibility fringes, but at their velocities quantum and classical predictions coincide (arXiv:2507.21211).