Superconductivity and  Quantum Spin Disorder  in Cuprates
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A fundamental connection between superconductivity 
and  quantum spin fluctuations in underdoped cuprates, is revealed. 
A variational calculation shows that
<em> Cooper pair hopping </em>
strongly reduces the local magnetization m_0.
This effect pertains to recent 
neutron scattering and  muon spin rotation measurements 
in which m_0 varies weakly with hole doping in the
poorly conducting regime,  but drops precipitously above the onset
of superconductivity.