We discuss a type of measurement in which a macroscopically large angular momentum (spin) is "created" nonlocally by the measurement of just a few atoms from a double Fock state. This procedure apparently leads to a blatant nonconservation of a macroscopic variable-the local angular momentum. We argue that while this gedankenexperiment provides a striking illustration of several counter-intuitive features of quantum mechanics, it does not imply a non-local violation of the conservation of angular momentum.
- Bose-Einstein condensate
- Quantum measurement