Taming the Rotating Wave Approximation”

The interaction between light and matter is one of the oldest research areas of quantum mechanics, and a field that just keeps on delivering new insights and applications. With the arrival of cavity quantum electrodynamics we can now achieve strong light-matter couplings which form the basis of most implementations of quantum technology. This has brought back into center stage one of the oldest approximations of quantum theory, the Rotating Wave Approximation (RWA). While the RWA is often very good and incredibly useful to understand light-matter interactions, there is also growing experimental evidence of regimes where it is a bad approximation. In my talk, I present a gentle historical introduction into the RWA, and consider the following question: for which experimental parameters is the RWA not good enough to match the demands of scalable quantum technology? I will show this not only depends on the ratio of the light-matter coupling strength and the oscillator frequency, but also on the average number of photons in the initial state. Furthermore, I will argue that the RWA also plays an important fundamental role, as it allows us to define resonance in quantum physics.