A Basic Example
Take a quantum system that can be in two possible states: for example, the polarisation of a photon. When the polarisation is measured, it could be horizontal, labelled as state, or vertical, state . Until its polarisation is measured the photon can be in a superposition of both these states, so its wavefunction, would be written:
The probability amplitudes of states and are α and β respectively. When the photon's polarisation is measured, it has probability of being horizontally polarised, and probability of being vertically polarised.
Therefore, a photon with wavefunction whose polarisation was measured would have a probability of 1/3 to be horizontally polarised, and a probability of 2/3 to be vertically polarised.
Read more about this topic: Probability Amplitude
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