Controlling spin properties of molecules with quantum fields: ab-initio methodologies for spin polaritons

Informations projet

QED-Spin

N° de convention de subvention: 101040197

DOI

10.3030/101040197

Date de signature de la CE 3 Decembre 2022

Date de début 1 Juin 2023

Date de fin 31 Mai 2028

Financé au titre de

• European Research Council (ERC)

Coût total

€ 1 499 754,00

Contribution de l’UE

€ 1 499 754,00

Coordonné par

UNIVERSITA DEGLI STUDI DI PERUGIA
Italy

Periodic Reporting for period 1 - QED-Spin (Controlling spin properties of molecules with quantum fields: ab-initio methodologies for spin polaritons)

Période du rapport: 2023-06-01 au 2025-11-30

Résumé du contexte et des objectifs généraux du projet

Strong light-matter interaction is now becoming an hot topic for the manipulation of molecular and materials properties.
In this context, opportunely designed optical devices (optical, superconductive or plasmonic cavities - Fig. 1) are used to confine light inducing
quantisation of the electromagnetic field and strong coupling between matter and photons.
This strong interaction brings to the formation of new hybrid states, called polaritons, having very different properties compared to the bare matter states.

Despite being very promising, realisation of matter control based on quantum fields is very challenging due to a complicated realisation and reproducibility of the experimental setting and by an incomplete
understanding of the physical phenomena lying at its foundations.
It is for this reason that theory represents a promising tool to shine light on the fundamental physics behind strong light-matter interaction.

Experiments aimed at the optical control of chemistry are mainly based on manipulation of electronic or vibrational properties of matter.
However, due to its electromagnetic nature light offers also the possibility to fine control magnetic properties of molecules.

The main goal of the QED-Spin project is to build new ab-initio methodologies to shade light on the fundamental physics behind optical manipulation of magnetic properties.
These theories will be used to investigate the effects induced by quantum field on the magnetic properties of molecules used in quantum computation, spin electronics, photochemical processes and exotic spectroscopies.
This challenge will be attacked by addressing the following objectives:

- Formal theory formulation, development and implementation of ab-initio methodologies for spin systems in quantum electrodynamics environments
- Study of the field induced effects on the spin properties of molecular systems used for quantum computing applications
- Study of the field induced effects on the intersystem crossing properties of molecules interesting for photochemical applications
- Developments of efficient techniques to include collective and relativistic effects crucial to obtain an accurate description of the system
- Development of embedding techniques to treat large spin systems coupled to quantum fields
- Formulation of the theory for the interaction between nuclear spins and quantum fields
- Simulation of NMR spectroscopy in quantum electrodynamics environments

The tools developed within this project will be made available to the entire scientific community through the open-source softwares eT and Pyscf.

Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent

Since June 2023, when the ERC QED-Spin project started, I started establishing and leading the Theoretical Polaritonic Chemistry team at the HI.
The project execution has called for a multidisciplinary team having competences in theoretical and computational chemistry, quantum field theory, quantum electrodynamics as well as programming and software design.
The research work performed by the group during the first 24 month of the grant is presented in the following:

- We have developed an extension of the QED coupled cluster (QED-CC) theory based on the minimal coupling Hamiltonian. In this case the full spacial dependence of the quantum field has been considered.
The approach, being based on a complex formalism, represents also the starting point for the inclusion of additional complex terms to the Hamiltonian (i.e. spin interactions, etc.).

- Application of QED-CC theory to investigate chiral molecules in chiral quantum fields. With this study we demonstrated that enantiomeric discrimination and enantioselectivity can be induced by quantum fields.

- Development of new theoretical techniques to include collective effects. This aspect is crucial to perform more realistic simulation directly comparable with the experiments.

- Development of the CC Cavity Born-Oppenheimer approximation. This approach provides a cost-effective way of describing the electromagnetic field.
This method can be particularly useful for ab-initio molecular dynamics simulations of systems in the vibrational strong coupling regime.

- We have formulated the exact polaritonic response theory for molecular systems in strong coupling conditions. This theory is crucial to have access to polaritonic excited states.
In its static form this theoretical frameworks provide access to field induced effects on magnetic properties such as electronic magnetizabilities, nuclear shieldings, J-J coupling etc.
This theory has been implemented in the Hartree-Fock and Coupled Cluster frameworks and applied to simulate spectra of molecular systems in optical cavities.
The strong coupling transformation has been also applied to include electron photon-correlation in an efficient manner.
The approach has been also formulated in a Real Time fashion to simulate electronic dynamics of molecules coupled to quantum field.

- Development of QED ab-initio methods to include effects coming from external magnetic fields and nuclear spins.
With this method we investigated the field induced effects on the magnetizability and nuclear shieldings of molecules and the implication on aromaticity.

- Development of a fully relativistic ab-initio formalism for polaritonic chemistry.
Using this theoretical framework we developed and implemented a polaritonic extension to the Dirac Hartree-Fock (Pol-DHF) approach.
This method allows for an accurate treatment of relativistic effects and in particular of spin-orbit coupling in the treatment of molecular systems coupled to quantum fields.
The inclusion of these effects is crucial for properly describing field effects on spin systems and intersystem crossing processes.

- We developed the quantum electrodynamics extension to the complete active space (QED-CASSCF) method.
The approach allows for the inclusion of static correlation into the treatment.
Similar methodology is crucial to properly describe systems like transition metal complexes containing heavy atoms.
Single molecule magnets usually used in the experiments for quantum computing applications fall in this class of complexes.

- We developed the Strong Coupling version of QED Møller-Plesset Perturbation theory. This method represents the first consistent perturbation theory
for coupled electron-photon systems.

Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)

The theoretical and computational tools developed in QED-Spin are not only useful to advance the field of polaritonic chemistry but they bring to a deeper
general knowledge of light-matter interaction in all its regimes.
It can clearly bring to significant advancements in the understanding of physical and natural processes involving light (photovoltaics, photosynthesis, etc.).

The strategies proposed by QED-Spin use electromagnetic field as an active tools to control the properties of matter in a totally non-intrusive and eco-friendly manner.
For this reason these techniques open new possibilities for sustainable processes.

The approaches developed in QED-Spin are aimed at proposing novel experimental devices for applications in quantum computation and other kind of electronics based on spins.
This might have significant economical implications.

Fig. 1: Scheme of different optical devices used for strong light-matter interaction