All-Possible-Couplings Approach to Measuring Probabilistic Context
Figure 1
Schematic representation of two spin- particles, e.g., electrons, in the singlet state (represented by
in quantum-mechanical notation) running away from each other. The directions
and
are detector settings for spin measurements (in our language, inputs). The measured spins
and
(outputs) in these directions are shown by rotation arrows: one direction of rotation (say, clockwise) represents “spin-up”
in one particle and “spin-down”
in the other. By the quantum theory, for any
,
(equivalently, expected value of
is
). The two measurements are made simultaneously (in some inertial frame of reference).