Journal of Statistical Physics, Vol. 85, Nos. 1/2, 1996. p. 193-210.
We discuss conditions for the absence of spontaneous breakdown of continuous symmetries in quantum lattice systems at T=0. Our analysis is based on Pitaevskii and Stringari's idea that the uncertainty relation can be employed to show quantum fluctuations. For one-dimensional systems, it is shown that the ground state is invariant under a continuous transformation if a certain uniform susceptibility is finite...