# QSpec-NewMat

ERC Advanced Grant "Quantum Spectroscopy: exploring new states of matter out of equilibrium"

This project addresses the development of novel theoretical and computational tools that utilize the quantum nature of light to understand and control quantum phenomena in complex systems in and out of equilibrium. Some examples of these processes include exciton-exciton interaction, quantum coherence, assisted energy and charge transport, photochemistry, and new states of matter.

The present project aims to build up the basic theoretical and computational machinery to allow quantum computations of the electronic and ionic dynamics of atomic, molecular or extended systems coupled to quantised electromagnetic fields and thereby set the stage for a new era in the first-principle computational modelling of light-matter interactions. To achieve this goal, we will combine the principles of time-dependent density functional theory (TDDFT) and quantum electrodynamics (QED) into a new quantum electrodynamical-DFT approach named as “QEDFT”.

Insight, design and control define the scientific rationale of the project, which will focus on the discovery of the general principles that describe and control systems far from equilibrium and orchestrate the behavior of many electrons and atoms to create new phenomena/states of matter. Besides developing and implementing the new theory of QEDFT, we will investigate atoms and molecules with quantum optical fields; whether and how selected laser pulses drive molecules and

solids into new states of matter that have no equilibrium counterpart. What happens when it enters these coherent states?

The objective is to identify the spectroscopic fingerprint of those new states. Which states arise in the strong light-matter coupling regime? e.g. hybridized states such as photon bound states, exciton/plasmon-polariton states, so far still undiscovered states. The long-term goal is to deliver an all-out theoretical and computational toolbox for QED-TDDFT applicable to complex molecular systems (like presently approachable by DFT and by TDDFT).

## Objectives

The objectives of this research project are as follows:

- To establish, develop and implement the density-functional approach of QEDFT to merge electronic structure and quantum optics and provide the necessary functional approximations to make it applicable.
- To investigate whether and how selected laser pulses drive molecules and solids into new states of matter that have no equilibrium counterpart. What happens to the material when it enters these coherent states? The objective is to identify the spectroscopic fingerprints of those new states.
- To investigate atoms and molecules with quantum optical fields: how does the photon field alter their properties? Which novel states arise in the strong light-matter coupling regime? (e.g., photon-bound states, exciton/plasmon-polariton states, or other unknown states). To investigate how to imprint photon correlations in matter. What are the implications for photoactive devices in energy conversion/storage?
- Develop a coherent control within QEDFT: control of molecular chemistry (e.g. entanglement between reactants, intersystem crossings); look for a polariton condensate and a laser of entangled photons.
- Explore coherent time-resolved spectroscopy: How does one control/modify decoherence/dissipation?
- Develop a framework to describe non-adiabatic dynamics of molecules driven far from equilibrium.
- To explore the possibility of constructing more accurate xc-approximations for conventional DFT by directly employing the fact that photons mediate the interaction between particles in QED.

## Participants

MAX PLANCK GESELLSCHAFT ZUR FOERDERUNG DER WISSENSCHAFTEN E.V. (MPG) - Prof. Angel Rubio Secades

UNIVERSIDAD DEL PAIS VASCO/ EUSKAL HERRIKO UNIBERTSITATEA (UPV/EHU) - Prof. Angel Rubio Secades