Concept of Orbital Entanglement and Correlation in Quantum Chemistry

A recent development in quantum chemistry has established the quantum mutual information between orbitals as a major descriptor of electronic structure. This has already facilitated remarkable improvements in numerical methods and may lead to a more comprehensive foundation for chemical bonding theory. Building on this promising development, our work provides a refined discussion of quantum information theoretical concepts by introducing the physical correlation and its separation into classical and quantum parts as distinctive quantifiers of electronic structure. In particular, we succeed in quantifying the entanglement. Intriguingly, our results for different molecules reveal that the total correlation between orbitals is mainly classical, raising questions about the general significance of entanglement in chemical bonding. Our work also shows that implementing the fundamental particle number superselection rule, so far not accounted for in quantum chemistry, removes a major part of correlation and entanglement seen previously. In that respect, realizing quantum information processing tasks with molecular systems might be more challenging than anticipated.

Automated summary

The recent development in quantum chemistry highlights the quantum mutual information between orbitals as a major descriptor of electronic structure, leading to significant improvements in numerical methods. By introducing physical correlation and separating it into classical and quantum parts, our work quantifies entanglement and raises questions about its general significance in chemical bonding. The implementation of the fundamental particle number superselection rule removes a major part of correlation and entanglement, suggesting that quantum information processing tasks with molecular systems may be more challenging than expected.