Optimal preparation of the W state for qubits with XY coupling
Dalton W. Jones, Armin Rahmani · Europhysics Letters (EPL) · 2026
Abstract Using simulated annealing, we find optimal protocols that evolve a simple product state into a three-qubit W state with a Hamiltonian that describes XY coupling and single-qubit gates, and determine the associated quantum speed limit. Applying Pontryagin's minimum principle, we fully characterize the optimal “bang-bang” protocols. While leakage affects performance, the protocols remain robust to implementation errors and operate well within relaxation and decoherence times. Our findings highlight Pontryagin's principle as a powerful tool for designing pulse shapes that directly link device interactions to specific quantum gates and target states.