Delayed-choice quantum erasure using Poisson-distributed photons.

Quantum superposition lies at the core of quantum mechanics and has been applied to various quantum technologies. Over the past few decades, Wheeler’s delayed-choice thought experiment has been extensively examined to explore the wave-particle duality of the complementary nature of quantum mechanics. The essence of the delayed-choice quantum eraser lies in the contradictory quantum property that violates the cause-effect relationship in classical physics. Our experiments present empirical evidence of the quantum eraser using coherent photon pairs provided in a noninteracting Mach-Zehnder interferometer for the polarization-basis control of output photons. The observed interference fringe is the direct proof of the quantum eraser, where the violation of the cause-effect relationship is due to the selective choices of the measurement events.