A qubit is a binary quantum state. The state can be well-determined (blue, orange) or undetermined (in superposition).

When an undetermined state is measured, the outcome is one of the two determined states, each with some probability. We represent this probability with two colored parts : blue (probability of outcome “0”) and orange (probability of outcome “1”).

Examples of physical systems that can be in an undetermined state:

  • The spin of an electron ( UP or DOWN )
  • The polarisation of a photon ( HORIZONTAL or VERTICAL )
  • The energy level of an ion ( fundamental state or excited state ).

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