  Wave-particle duality is the most fundamental description of the nature of a
quantum object which behaves like a classical particle or wave depending on the
measurement apparatus. On the other hand, entanglement represents nonclassical
correlations of composite quantum systems, being also a key resource in quantum
information. Despite the very recent observations of wave-particle
superposition and entanglement, whether these two fundamental traits of quantum
mechanics can emerge simultaneously remains an open issue. Here we introduce
and experimentally realize a scheme that deterministically generates
wave-particle entanglement of two photons. The elementary tool allowing this
achievement is a scalable single-photon setup which can be in principle
extended to generate multiphoton wave-particle entanglement. Our study reveals
that photons can be entangled in their dual wave-particle nature and opens the
way to potential applications in quantum information protocols exploiting the
wave-particle degrees of freedom to encode qubits.
