Vibrational Entanglement through the Lens of Quantum Information Measures

TL;DR

This paper applies quantum information measures to vibrational wave functions, revealing mode couplings and correlations in molecules with complex spectra, especially in the presence of anharmonicities and resonances.

Contribution

It introduces vibrational entanglement measures and applies them to analyze complex vibrational spectra of molecules using advanced computational methods.

Findings

Identified strongly coupled vibrational modes using entropies.

Characterized vibrational correlations in CO2's ground and excited states.

Detected entanglement signatures of Fermi resonance and degeneracies.

Abstract

We introduce a quantum information analysis of vibrational wave functions to understand complex vibrational spectra of molecules with strong anharmonic couplings and vibrational resonances. For this purpose, we define one- and two-modal entropies to guide the identification of strongly coupled vibrational modes and to characterize correlations within modal basis sets. We evaluate these descriptors for multi-configurational vibrational wave functions which we calculate with the n-mode vibrational density matrix renormalization group algorithm. Based on the quantum information measures, we present a vibrational entanglement analysis of the vibrational ground and excited states of CO2, which display strong anharmonic effects due to the symmetry-induced and accidental (near-) degeneracies. We investigate the entanglement signature of the Fermi resonance and discuss the maximally entangled state arising from the two degenerate bending modes.