An Introduction to Quantum Optics

14Bell’s Theorem and Bell’s Inequality Measurement

In the early 1950s, Bohm simplified the 1935 EPR state to discrete spin state by introducing a singlet state of two spin 1/2 particles:

where the kets |↑right and | ↓ represent states of spin “up” and spin “down,” respectively, along an arbitrary direction. For the EPR-Bohm state, the spin of neither particle is determined; however, if one particle is measured to be spin up along a certain direction, ...