Imagine a world where quantum physics and quantum technology collide to create a new realm of possibilities. Thanks to researchers at the Max Planck Institute for the Science of Light (MPL) and Jozef Stefan Institute in Ljubljana, Slovenia, we are entering a new era with the demonstration of spontaneous parametric down-conversion (SPDC) in a liquid crystal. This groundbreaking discovery, recently published in Nature, paves the way for a revolutionary generation of quantum sources that are both efficient and electric-field tunable.
One of the most powerful tools in quantum photonics is the ability to split a single photon into two. This process, known as SPDC, not only creates entangled photon pairs but also opens the door to a myriad of complex light states crucial for optical quantum technologies.
Traditionally, SPDC has only been achievable in solids due to the requirement of central symmetry breaking. However, researchers have unearthed a unique class of liquid crystals called ferroelectric nematic liquid crystals that possess the necessary asymmetric structure. These fluidic materials can be re-oriented by an external electric field, altering the polarization and generation rate of photon pairs.
By utilizing samples prepared at the Jozef Stefan Institute and a ferroelectric nematic liquid crystal synthesized by Merck Electronics KGaA, scientists at the Max Planck Institute successfully implemented SPDC in a liquid crystal for the first time. The efficiency of entangled photon generation rivals that of the best nonlinear crystals, such as lithium niobate, when of similar thickness. Remarkably, a mere few Volts of electric field was all it took to control the generation and polarization properties of photon pairs, marking the dawn of a new era for quantum light sources: flexible, tunable, and highly efficient.