Extreme cryogenic piezoelectric and electrooptic nonlinearities in strontium titanate

Optical fields and mechanical motion are common degrees of freedom utilized in a variety of cryogenic hybrid quantum systems. Here, I will describe our work on the material strontium titanate (STO), which displays record high electro-optical and piezoelectric nonlinearities at the low temperatures where quantum devices operate. The strength of these interactions is related to a low temperature quantum paraelectric phase, which unlocks stronger coupling of motion and light to electric fields. In this material, the bare coupling coefficients exceed lithium niobate by over an order of magnitude. In addition, these effects can be further enhanced by at least an additional factor of two with precise tuning of the ferroelectric-paraelectric phase transition. These improvements are supported by theory, outlining a path to even stronger materials nonlinearities that could be harnessed in everything from photonic switches and optomechanical devices to microwave-to-optical transducers.