The quantum NOT gate swaps the state of and , i.e. it maps:
As a result, this gate also inverts the probability of measuring 0 or 1, e.g.
  • if the old probability of 0 was 0, then it becomes 1
  • if the old probability of 0 was 0.2, then it becomes 0.8
Figure 1. Quantum NOT gate symbol. Source.