Measuring particle A correlates particle B at once, yet not a single bit travels between them that way: each side still sees random 50/50 outcomes, and the correlation surfaces only when the two logs are compared over an ordinary channel. The correlation against detector angle follows −cos θ, and the CHSH combination built from it passes the classical bound of 2 on its way toward 2√2 ≈ 2.83, enough to rule out every local hidden-variable theory. Entanglement with the environment drags that number back under 2, which is exactly what plagues quantum computers.
Measuring particle A correlates particle B at once, yet not a single bit travels between them that way: each side still sees random 50/50 outcomes, and the correlation surfaces only when the two logs are compared over an ordinary channel. The correlation against detector angle follows −cos θ, and the CHSH combination built from it passes the classical bound of 2 on its way toward 2√2 ≈ 2.83, enough to rule out every local hidden-variable theory. Entanglement with the environment drags that number back under 2, which is exactly what plagues quantum computers.
Related topics in Particle & Quantum