MEC · Macroscopic Entanglement in Crystals

Quantum theory is often presented as the theory of the microscopic world. However, over the last decade, things have changed dramatically. Today one can envision manipulating large quantum systems, while mastering individual degrees of freedom. It is thus timely to ask entirely new questions on the quantum/classical transition and to support these by experimental investigations of large entanglement. The vision of this project is to explore conceptually, experimentally and technologically the limits of large entanglement of macroscopically distinguishable quantum states. We propose to demonstrate entanglement between two or more macroscopic crystals with hundreds of entanglement bits (e-bits), hundred of thousands of excitations and billions of ions. For this purpose, we’ll use Neodymium doped YSO crystals and our AFC (Atomic Frequency Comb) protocol for multimode quantum memories.Since entanglement is the signature of quantumness, this project will demonstrate “macroscopic” entanglement and help sharpening the meaning of “large” and “macroscopic”. By combining theory and experiments, questions like “What is large entanglement?” and “What deserves to be called entanglement between macroscopic systems?” will receive new insightful answers. This will deepen our understanding of Nature and in particular of the intricate meaning of meso- and macroscopic.Two further goals of this project are to demonstrate large entanglement between two crystals separated by tens of kilometres, and to teleport many qubits stored in a crystal to a distant one.Although this project is on fundamental questions, it will also contribute to improving the quantum memories required for continental scale ultra-secure quantum communications. We expect other surprising applications, in particular the high sensitivity of large entanglement to various decoherence mechanisms can be turned positively into quantum sensors.