Quantum entanglement is a state in which particles are entwined with each other. In this entwined state, the properties of one particle influence the other, even when they aren't physically close to each other. This phenomenon has often been observed in small quantum systems with only a few particles in them, where researchers can use it to store and process quantum information. Rice University professor Qimiao Si is interested in understanding and applying quantum entanglement to macroscopic systems with vast numbers of particles.