Light-Matter Systems

Undriven

Driven

Controlled emergence of phases of matter in strongly correlated systems through external driving has been instrumental not only in advancing our understanding of many-body physics but also in the search for new functionalities for future quantum technologies. For example, shining a laser light at a superconductor can reveal glimpses of superconductivity at room temperature.

Unfortunately, in most cases, the complexity of quantum many-body systems, especially those in solid-state platforms, poses a substantial challenge to the fundamental understanding of genuine non-equilibrium phenomena. It is then desirable to observe and characterize dynamical control and emergence of phases in a relatively simple platform, such as ultracold atomic systems, to better understand them at a microscopic level.

Ultracold atoms cooled down to temperatures below a hundred nanokelvin are some of the coldest objects in the universe. We combine the physics of cold atoms and quantum optics, making matter interact with light, to further our understanding of many-body physics and discover various interesting phenomena.

In collaboration with experimentalists, we study various phases in an atom-cavity system consisting of a Bose-Einstein condensate of atoms placed inside a high-finesse optical cavity. This platform serves as an example of a light-matter system that can be described by relatively simple mathematical descriptions, such as the Dicke model. In fact, some aspects of the transversely pumped atom-cavity system, such as the phase transition it hosts, can be understood as an emulation of the fundamental properties of the Dicke model.

Using various models of light-matter systems and the atom-cavity platform, we explore the rich physics arising from the complex interplay between interaction, dissipation, and driving. Some examples of interesting emergent phenomena, which we have observed theoretically and experimentally, include time crystals, condensation in a dark state, and dynamical control of equilibrium properties.

Publication Highlights

Observation of a continuous time crystal, P. Kongkhambut, J. Skulte, L. Mathey, J. G. Cosme, A. Hemmerich, H. Keßler, Science, (2022). [arXiv]

News articles and interviews:

"Researchers observe continuous time crystal" (Phys.org)

"A new kind of time crystal has been created and lasts 10 milliseconds" (NewScientist)

Observation of a dissipative time crystal, H. Keßler, P. Kongkhambut, C. Georges, L. Mathey, J. G. Cosme, A. Hemmerich, Physical Review Letters 127, 043602, (2021) [Editors' Suggestion]. [arXiv]

Commentary articles:

"Time crystals in Open Systems" by Z. Gong and M. Ueda

"Quantum time crystals open up" by P. Ball

News articles and interviews:

"The first experimental realization of a dissipative time crystal" (Phys.org)

"Zu verrückt, um falsch zu sein" (Die Zeit)

"Auf den Spuren von Raum und Zeit" (Forschung und Lehre)

Torus bifurcation of a dissipative time crystal, J. G. Cosme, P. Kongkhambut, A. Bölian, R. J. L. Tuquero, J. Skulte, L. Mathey, A. Hemmerich, H. Keßler, Physical Review Letters 134, 223601, (2025). [arXiv]
Observation of a phase transition from a continuous to a discrete time crystal, P. Kongkhambut, J. G. Cosme, J. Skulte, M. A. Moreno Armijos L. Mathey, A. Hemmerich, H. Keßler, Reports on Progress in Physics, (2024).
Condensate formation in a dark state of a driven atom-cavity system, J. Skulte, P. Kongkhambut, S. Rao, L. Mathey, H. Keßler, A. Hemmerich, J. G. Cosme, Physical Review Letters 130, 163603, (2023). [arXiv]
Realization of a periodically driven open three-level Dicke model, P. Kongkhambut, H. Keßler, J. Skulte, L. Mathey, J. G. Cosme, A. Hemmerich, Physical Review Letters 127, 253601, (2021). [arXiv]
Light-induced coherence in an atom-cavity system, Ch. Georges, J. G. Cosme, L. Mathey, A. Hemmerich, Physical Review Letters 121, 220405, (2018).
Dynamical Control of Order in a Cavity-BEC System, J. G. Cosme, Ch. Georges, A. Hemmerich, L. Mathey, Physical Review Letters 121, 153001, (2018).

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