Wave-particle superposition of distinct atomic spin excitations

Wave-particle duality is the most essential nature of light, and the fact that the detection apparatus determines the observed wave or particle behavior is one of the most counterintuitive features of quantum mechanics. Recent progress in this direction has revealed novel and peculiar phenomena of photonic wave-particle morphing and wave-particle superposition, which provide a deep understanding of the wave-particle duality for photons. However, it remains an open question whether this new conception can be extended to a more complex physical system, such as an atomic system. We here report an experimental realization of the wave-particle superposition of distinct atomic spin excitations in a cold atomic ensemble by using multiplexed quantum memory. The quantum behavior of wave-particle superposition for matter is observed and verified. Our scheme further provides a benchmark understanding of the wave-particle duality in matter systems.