Slit Experiment

A question about particle/wave duality and the slit experiment.

For photons and electrons, trying to put a particle detector at one of the slits collapses the wave function.

Is there a limit to the size/mass of the particle so that the wave function cannot be observed?

Like, say, throwing a beam of hydrogen ions through the slits?

Molecules?

Yes, there is a practical limit. This is because it is the wavelengths of the particles that determine the interference patterns. Already with electrons you have to put your slits pretty close together. Eventually your grating has to be so small that you can’t build it at all.

I don’t know off-hand what the largest particle is for which the effect has been observed. In principle you can go as large as you want, but in practice the exceedingly small wavelengths of large objects prevent, say, you or I from being quantum particles in any practical sense.