  The many-body dispersion (MBD) framework is a successful approach for
modeling the long-range electronic correlation energy and optical response of
systems with thousands of atoms. Inspired by field theory, here we develop a
second-quantized MBD formalism (SQ-MBD) that recasts a system of atomic quantum
Drude oscillators in a Fock-space representation. SQ-MBD provides (I) tools for
projecting observables (interaction energy, transition multipoles,
polarizability tensors) on coarse-grained representations of the atomistic
system ranging from single atoms to large structural motifs, (ii) a
quantum-information framework to analyze correlations and (non)separability
among fragments in a given molecular complex, and (iii) a path toward the
applicability of the MBD framework to molecular complexes with millions of
atoms. The SQ-MBD approach offers novel insights into quantum fluctuations in
molecular systems and enables direct coupling of collective plasmon-like MBD
degrees of freedom with arbitrary environments, providing a tractable
computational framework to treat dispersion interactions and polarization
response in intricate systems.
