Physicists discover easy way to measure entanglement--on a sphere

(Phys.org)--Quantum entanglement--which occurs when two or more particles are correlated in such a way that they can influence each other even across large distances--is not an all-or-nothing phenomenon, but occurs in various degrees. The more a quantum state is entangled with its partner, the better the states will perform in quantum information applications. Unfortunately, quantifying entanglement is a difficult process involving complex optimization problems that give even physicists headache...