A qubit is a two-state quantum system described by amplitudes, not by a simple probability list.
Every gate, histogram bar, and Bloch sphere arrow in the simulator shows a different view of the same quantum state. If you understand what the state is, the rest of the interface becomes much easier to read.
A classical bit has a definite value: 0 or 1. A qubit is different. Before you measure it, its state is described by two amplitudes -- one for and one for . These amplitudes are not probabilities. They are the deeper quantities that produce probabilities when you square their sizes. They also carry phase, which is why a qubit is richer than a random coin flip.
Think of a recipe versus a meal. The quantum state is the recipe -- it tells you what outcomes are possible and how they relate. The measurement result (0 or 1) is the meal you actually serve. The recipe contains more information than any single meal.
The symbols and are complex amplitudes. Their squared magnitudes give the measurement probabilities in the standard basis: P(0) = ||² and P(1) = ||². Because and are complex numbers, they also encode phase information. Two states can have the same measurement probabilities but different phases, which means they will behave differently in future operations.
Open the simulator and see this concept in action. Watch how the state changes and compare it to what you just learned.
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