Frank Isakson Prize for Optical Effects in Solids talk: Nonlinear light matter interaction at TeraHerz Frequencies: from observation to control.

In this talk, I will present an overview of our recent research in the non-equilibrium control of quantum materials. We will especially emphasize that coherent electromagnetic radiation, which has been traditionally used as a spectroscopic tool to observe the symmetry and dynamics of solids, can now be used to control collective properties of materials. In this context, I will discuss the importance of strong field TeraHertz pulses, which can drive cooperative dynamics and switch between different forms of order. Some the phases induced by light are known to exist at equilibrium, although some are hidden and not known. A case in point has been the discovery of transient superconducting fluctuations at temperatures far in excess of the thermodynamic transition temperature, induced by these non-equilibrium driving. I will also emphasize the role of modern infrastructure and new instrumentation, of which the X-ray Free Electron Laser is as the most spectacular.