This page contains an interactive applet, which will only be run if your browser supports the Java programming language. The applet is about 4 K.
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,
, 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.
