The applet below allows you to perform three simulated experiments, which
show how quantum behaviour is hidden when a system becomes entangled, but
can be recovered by observations on the complete system.
(These are not realistic experiments, but they serve as simple illustrations of the
basic idea. Real experiments have been performed to verify these principles, mostly
using photons.)
- Experiment 1. Electrons are produced in an equal superposition of
spin up and spin down, with the phase,
θ, between the two components
varying in a controlled fashion. The electrons’ spins are measured along the x-axis
(spin right or spin left), and the average value for their spin
is plotted against the phase.
- Experiment 2. The electrons are produced in the same fashion as in
experiment 1, but now they are entangled with positrons by a process that
guarantees that a spin up electron would always be accompanied by a spin up
positron, and a spin down electron would always be accompanied by a spin down
positron. Again, the electrons’ x-axis spins are measured, and the average value
plotted against the phase.
- Experiment 3. Electrons are produced, and entangled with positrons
as in experiment 2, but now the positrons’ x-axis spins are also measured, and multiplied
by the electrons’. The average value of this quantity is plotted against the phase.
