Entanglement-enabled delayed choice experiment

International audienceWave-particle complementarity is one of the most intriguing features of quan- tum physics. To emphasize this measurement apparatus dependent nature, ex- periments have been performed in which the output beam-splitter of a Mach- Zehnder interferometer is inserted or removed after a photon has already en- tered the device. A recent extension suggested using a 'quantum beam-splitter' at the interferometer's output. We realize this using pairs of polarization en- tangled photons. One photon is tested in the interferometer and is detected, while the other allows determining whether wave, particle, or intermediate be- havior have been observed. Furthermore, this allows continuously morphing the tested photon's behavior from wave like to particle like. This illustrates the inadequacy of a naive wave or particle description of light