Testing Higher-Order Quantum Interference with Many-Particle States

Quantum theory permits interference between indistinguishable paths but, at the same time, restricts its order. Single-particle interference, for instance, is limited to the second order, that is, to pairs of single-particle paths. To date, all experimental efforts to search for higher-order interferences beyond those compatible with quantum mechanics have been based on such single-particle schemes. However, quantum physics is not bound to single-particle interference. We here experimentally study many-particle higher-order interference using a two-photon-five-slit setup. We observe nonzero two-particle interference up to fourth order, corresponding to the interference of two distinct two-particle paths. We further show that fifth-order interference is restricted to 10(-3) in the intensity-correlation regime and to 10(-2) in the photon-correlation regime, thus providing novel bounds on higher-order quantum interference.

Automated summary

Quantum theory allows interference between indistinguishable paths but with restricted order. Experimental efforts to search for higher-order interference beyond quantum mechanics have mainly focused on single-particle schemes, but this study shows that many-particle interference can display higher-order interference.