Our paper on Lindblad Master Equation Capable of Describing Hybrid Quantum Systems in the Ultrastrong Coupling Regime has been published in Physical Review Letters!

The ultrastrong coupling (USC) regime, where light-matter coupling strength becomes comparable to transition frequencies, presents significant challenges for theoretical treatments and prevents the use of many common approximations. In this work, we demonstrate an approach that can describe the dynamics of hybrid quantum systems in any regime of interaction for an arbitrary electromagnetic environment.

We extend our previous few-mode quantization method to the case of USC and show that even such systems can be treated using a Lindblad master equation where decay operators act only on the photonic modes. The key is ensuring that the effective spectral density of the EM environment is sufficiently suppressed at negative frequencies.

We demonstrate the validity of our framework by comparing it to current state-of-the-art master equations for a simple model system, and then study a realistic nanoplasmonic setup where existing approaches cannot be applied.

This work was led by Maksim Lednev and done in collaboration with Francisco J. García-Vidal.