Making ab initio QED functional(s): Nonperturbative and photon-free effective frameworks for strong light-matter...

Area of Science:

• Quantum physics
• Computational chemistry
• Materials science

Background:

• Strong light-matter coupling is key for controlling quantum matter.
• Existing ab initio methods struggle with the computational demands of quantized light-matter interactions.
• The distinct Hilbert spaces of light and matter pose significant challenges.

Purpose of the Study:

• To develop a nonperturbative, photon-free formulation of quantum electrodynamics (QED) in the long-wavelength limit.
• To create a computationally tractable framework for ab initio studies of quantum matter under strong light-matter coupling.
• To enable accurate descriptions of quantum systems interacting with quantized light fields.

Main Methods:

• Developed a photon-free formulation of QED solely on the matter Hilbert space.
• Extended quantum mechanics to recover exact QED results in specific limits (zero/infinite coupling, infinite frequency, homogeneous).
• Devised approximations for quantum-electrodynamical density-functional theory (QEDFT) and extended the ansatz to minimal-coupling and nonadiabatic problems.

Main Results:

• The formulation provides an accurate starting point for ab initio methods.
• Achieved constructive accuracy improvements beyond standard QED.
• Introduced a computationally simple QEDFT functional capturing transverse photon coupling, frequency, and polarization dependence.

Conclusions:

• The new QED formulation and QEDFT functional enable accurate, efficient ab initio studies of quantum matter with quantized light.
• The method is applicable to periodic systems and various coupling regimes.
• Facilitates the control of quantum matter through strong light-matter interactions.