AbstractThe fermionic second order reduced density matrix with complex dilation and thermalization describes generally quantum correlation effects in condensed matter. Connection with recent experiments on high‐Tc copper‐oxide superconductors is made. The following experimental results are explained from first theoretical principles: (1) Quantum correlation contributions to the energy gap in agreement with e.g. precise infrared experiments. (2) The universal relation between Tc and ns/m* (carrier density over effective mass) [Uemura et al., Phys. Rev. Lett. 62, 2317 (1989)]. (3) The saturation of Tc with increasing carrier density. (4) The considerable absorption “in” the energy gap. A prediction concerning the sudden breakdown of superconductivity at a specific (high) carrier density follows from the general theory. All the above results are independent of the specific (and still unknown) Cooper pair formation mechanism.