  Nearly a decade ago the old controversy about possible superfluid flow in the
ground state of solid He4 was revived by the apparent experimental observation
of such superflow. Although the experimentalists have recently retracted, very
publicly, some of the observations on which such a claim was based, other
confirming observations of which there is no reason for doubt remain on the
record. Meanwhile theoretical arguments bolstered by some experimental evidence
strongly favor the existence of supersolidity in the Bose-Hubbard model, and
these arguments would seem to extend to solid He. The true situation thus is
apparently extraordinarily opaque. The situation is complicated by the fact
that all accurate simulation studies on Heuse the uniform sign hypothesis which
confines them to the phase-coherent state, which is, in principle, supersolid,
so that no accurate simulations of the true, classical solid exist. There is
great confusion as to the nature of the ground state wave-function for a bose
quantum solid, and we suggest that until that question is cleared up none of
these dilemmas will be resolved.

Statistical Mechanics