# Surprisal Analysis-Based Compaction of Entangled Molecular States of Maximal Entropy

## TL;DR

This paper uses surprisal analysis to simplify the description of entangled molecular states under ultrafast excitation.

## Contribution

The novelty lies in applying surprisal analysis and maximal entropy formalism to compactify entangled molecular states.

## Key findings

- Surprisal analysis simplifies constraints in the sudden approximation of ultrafast dynamics.
- The compaction reduces On2 to On constraints for vibronic states in N2.
- Von Neumann entropy confirms the accuracy of the simplified model.

## Abstract

An attosecond optical pulse can entangle coherently related states of different characters, such as electronic and vibrational, in a molecular system. Using a quantum information theoretic approach, we explicitly define and discuss the surprisal of such a system in the maximal entropy formalism and identify the constraints and their conjugate Lagrange multipliers. Surprisal analysis shows how these constraints become fewer and simpler in the sudden approximation of the dynamics, a limit often valid for an ultrafast excitation. The optically accessible lower electronic states of N2 are used as a numerical example to show the compaction of the dynamics from On2 down to On constraints, where n is the number of vibronic states. The von Neumann entropy is used to confirm the fidelity of the compaction.