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Conditional (if)

If conditional tile from the Operations catalog

The if tile applies an operation only when a classical condition is true - the bridge between a measurement result and later quantum operations, based on classical, not quantum, control.
Qubits Depends on the operation it wraps
Parameters A classical register/bit and the value to compare against
Category Classical control flow, not a quantum gate
Also called Classically-controlled gate, c_if

What it does

A conditional operation checks the current value of a classical bit (usually set by an earlier measurement) and only applies its attached gate when that value matches the condition. Unlike Control - which conditions a gate on a qubit's quantum state without collapsing it - a conditional checks an already-measured, classical value, so there's no superposition involved in the decision itself.

Example

Measure q[0] into c[0], then apply X to q[1] conditioned on c[0] == 1: whatever definite value the measurement produced classically decides whether the X runs. This pattern shows up in protocols like quantum teleportation, where a receiver's correction gates depend on a sender's measurement outcomes.

Other notations

Naming conventions across ecosystems; exact syntax can vary by library version, and this does not claim to be Qompile's generated output unless otherwise noted.

Language Typical form
OpenQASM 2.0 if (c[0] == 1) x q[1];
Qiskit circuit.x[q[1]].c_if[c, 1]
Cirq cirq.X(q[1]).with_classical_controls('c0')
Q# if (M(q[0]) == One) { X(q[1]); }