The review article by Dr. Forn-Díaz and co-workers from Bilbao and Huston titled “Ultrastrong coupling regimes of light-matter interaction” has finally been published in the prestigious journal Reviews of Modern Physics.
This article reviews the state of the field in the regime in which light and matter interact so strongly that the whole system becomes a new entity with exotic properties. The review particularly focuses on the experimental progress in the last decade on the fields of superconducting qubits coupled to microwave photons and polaritons in semiconductor quantum wells coupled to infrared radiation. This field keeps gathering interest due to its fundamental intricacies (recent works studying the gauge invariance is just one more example), and the potential to find applications in quantum technologies. In fact, Dr. Forn-Díaz is leading a proposal for a European call to fund a project on ultrastrong couplings and quantum technologies.
The landmark of the review is the evolution of the coupling strength normalized to the bosonic mode frequency over time and for many fields. Clearly, experiments have finally managed to enter the USC regime just very recently, and a whole new field is ready to be explored.