Genuine Quantum Strong Mpemba Effect by Eliminating Coherence

Relaxation does not always reward patience: under certain conditions, a system initially farther from equilibrium can relax faster than one initially closer, a counterintuitive phenomenon known as the Mpemba effect. A conceptually transparent mechanism underlying this effect is the strong Mpemba effect, which commonly requires a unique slowest decay mode. However, for the Davies map, this condition is relaxed: the degenerate slowest modes are purely coherent. This allows the strong Mpemba effect to be realized by strategically eliminating coherence from the initial state. In this Letter, we design and implement a fully controllable optical setup to simulate the Davies map, whose validity is confirmed by verifying the semigroup property of the dynamics. We further demonstrate a genuine quantum strong Mpemba effect in the minimal quantum system, a single qubit. Our results experimentally confirm the key role of quantum coherence in this anomalous thermal relaxation. Moreover, our experimental setup provides a versatile platform for exploring quantum thermodynamics and a wider range of open-system dynamics.