Motivated by the Banach fixed-point theorem, we construct a single-qubit channel, a rotated convex combination of the depolarizing and amplitude damping channels, whose repeated application drives any initial state to any chosen target state. Includes an interactive Bloch-sphere explorer of the trajectory.
A scalable, SPAM-robust protocol for estimating the process fidelity of a fixed cycle of parallel gates. We introduce the CB protocol, explain how randomized compiling tailors noise into Pauli channels, and analyze when the gate-independence assumption can be relaxed.