Accessing electronic correlations by half-cycle pulses and time-resolved spectroscopy

TL;DR

This paper explores how ultrashort electromagnetic pulses can probe electronic correlations in many-body systems by linking the pulse's effect to the two-body reduced density matrix, enabling direct measurement of bond-dependent correlations.

Contribution

It extends the application of non-resonant pulses from single-electron to many-body systems, proposing a method to measure electronic correlations via survival probability in a pump-probe scheme.

Findings

Numerical simulations for molecular systems demonstrate the method's effectiveness.

Survival probability correlates with the two-body reduced density matrix.

Electronic correlation strength varies with bond length and can be measured.

Abstract

Ultrashort non-resonant electromagnetic pulses applied to effective one-electron systems may operate on the electronic state as a position or momentum translation operator. As derived here, extension to many-body correlated systems exposes qualitatively new aspects. For instance, to the lowest order in the electric field intensity the action of the pulse is expressible in terms of the two-body reduced density matrix enabling thus to probe various facets of electronic correlations. As an experimental realization we propose a pump-probe scheme in which after a weak, swift "kick" by the non-resonant pulse the survival probability for remaining in the initial state is measured. This probability we correlate to the two-body reduced density matrix. Since the strength of electronic correlation is bond-length sensitive, measuring the survival probability may allow for a direct insight into the bond-dependent two-body correlation in the ground state. As an illustration, full numerical calculations for two molecular systems are provided and different measures of electronic correlations are analyzed.