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Intermediate12 min read

Gates & Circuits

Every quantum gate is a rotation. Every circuit is a sequence of rotations you can read left to right.

Before this: Interference: Where the Power Comes From

In this lesson you’ll learn

  • Explain why quantum gates must be unitary, and what that buys you
  • Recognise X, Y, Z, H, S, T and the rotation gates by their action on the Bloch sphere
  • Read a circuit diagram and say what "controlled" actually means

Predict before you read on

The classical AND gate maps two input bits to one output bit: inputs 00, 01 and 10 all give output 0. Can there be a quantum gate with that shape — two qubits in, one qubit out?

Commit to an answer — the next section is the payoff.