We explore quantum + classical theories
of molecules, materials, and their interaction with light


Quantum mechanics reigns at the atomic scale, but classical mechanics continues to successfully predict large-scale phenomena. As such, we have two complementary theories with each their own realm of applicability. But what sets the quantum–classical boundary? Developments in quantum materials and quantum information science are increasingly pushing quantum behaviors into scales formerly attributed to the classical realm. Conversely, one may wonder how far we can extend the success of classical mechanics into the quantum realm.

These are questions driving the research in The Tempelaar Team. By exploring the interface of quantum and classical theories, we seek to better understand the foundations of both quantum and classical behaviors, to replace computationally-expensive quantum models by inexpensive classical models, and to construct new hybrid models invoking both classical and quantum mechanics. In doing so, we seek to optimally contribute to breakthroughs in chemistry, physics, and materials science by targeting well-defined scientific problems and by closely collaborating with experimental scientists.

Quantum materials

In some materials, quantum behaviors emanating from the constituent electrons survive at macroscopic scales, giving rise to unusual material properties with far-reaching technological implications. How do electronic quantum effects survive in an environment of vibrating nuclei? We seek to address this question by developing new mixed quantum–classical models that go beyond the Born–Oppenheimer approximation in realistically capturing electron–nuclear interactions within a material.

Spin & chirality

Electrons, nuclei, and photons each carry a spin degree of freedom which can be used to store and process quantum information. Quantum information applications oftentimes rely on coupling photonic spin states to chiral excitations in matter, which relies in chiroptical interactions. We seek to amplify and control such interactions by using optical resonators. This poses the need for novel chiroptical materials, some of which we have helped develop.


Strong coupling of quantum excitations in matter to confined optical fields gives rise to a new hybrid light–matter state called polariton. Polariton formation radically changes the properties of the host materials, with tunability afforded by the applied optical field, opening a new realm for chemical control and materials engineering. We study the behavior of polaritons through the development of full quantum models as well as models that represent optical fields classically through Maxwell's equations.

The team

Roel Tempelaar
Principal investigator

Anna Bondarenko
Postdoctoral researcher

Antonio Garzón Ramírez
Postdoctoral researcher

Ming-Hsiu Hsieh
Graduate student (2021)

Alex Krotz
Graduate student (2020)

Chientzu Lin
Graduate student (2022)

Ken Miyazaki
Postdoctoral researcher

Andrew Salij
Graduate student (2019)

Connor Terry Weatherly
Graduate student (2020)

Former mentees

Ian Dunn

Benedikt Kloss
Flatiron Institute

Justin Provazza




Alexis Foster (program assistant),

The Tempelaar Team is part of the Chemistry Department, and one of the various groups practicing Theoretical Chemistry at Northwestern University.

© The Tempelaar Team