Le 12/01/2019 =C3=A0 12:01, Jos Bergervoet a =C3=A9crit=C2=A0:

The human eye can detect a SINGLE PHOTON...

See:

Direct detection of a single photon by humans
https://www.nature.com/articles/ncomms12172

That is the absolute minimum I would say.

Now, what is the quantum particle of gravity???

Well, better leave that question open isn't it?

:-)