Correlation energy as a measure of non-locality: Quantum entanglement of helium-like systems

In this work we discuss the essential quantum origin of correlation energy as measured through the wave function regardless of any extrinsic Hamiltonian. The ambiguous physical meaning of correlation energy is clarified by identifying the non-dynamical correlations inherent in the system state of Slater rank different than one with the quantum phenomenon of nonlocality. This is achieved by relating correlation energy to entanglement as measured through the von Neumann and the linear entropies. Indeed, for helium-like systems with varying Z we observe one-to-one correspondence between entanglement and correlation energy. We present numerical evidence of the linear relation between the correlation energy E-corr and the quantum entanglement for various members of the helium isoelectronic series by use of highly correlated wave functions of configuration-interaction type. Copyright (C) EPLA, 2015