W State for Any n

Unlike GHZ, a W state keeps entanglement among the remaining qubits when one is lost. It is also harder to prepare: you have to split a single excitation evenly across n qubits.

Objective

prepare_w_state(num_qubits) returns a circuit preparing (|10...0> + |01...0> + ... + |0...01>)/sqrt(n) for any n from 1 to 6.

Constraints

• No initialize / state_preparation shortcuts, including inside custom gates.

Entry Point

Checks

• Exports prepare_w_state(num_qubits).
• Prepares exact W states for 1 to 6 qubits.