Parameterized Gates
A parameterised gate is a gate with a number dial: RY(θ) turns a definite 0 into a state that reads 1 with probability sin²(θ/2). The circuit structure stays fixed while the numbers change — that separation underlies parameter sweeps and variational methods.
What is a parameterised gate?
Gates like X and H are switches: they do one fixed thing. A parameterised gate is a dial: the gate's structure is fixed, but a number you supply sets how far it turns.
The number is an angle in radians — the angle unit in which π ≈ 3.1416 means half a turn and 2π means a full turn. In circuit JSON the angle is stored as a plain resolved number, such as 1.0472 for π/3, not as a formula.
The three basic dials are RX(θ), RY(θ) and RZ(θ), rotations about three different axes of the qubit's state space. This lesson uses RY because its effect on readout probabilities is the easiest to compute by hand, and RZ because its effect is the easiest to get wrong.
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