  Photonic quantum technologies such as quantum cryptography, photonic quantum
metrology, photonic quantum simulators and computers will largely benefit from
highly scalable and small footprint quantum photonic circuits. To perform fully
on-chip quantum photonic operations, three basic building blocks are required:
single-photon sources, photonic circuits and single-photon detectors. Highly
integrated quantum photonic chips on silicon and related platforms have been
demonstrated incorporating only one or two of these basic building blocks.
Previous implementations of all three components were mainly limited by laser
stray light, making temporal filtering necessary or required complex
manipulation to transfer all components onto one chip. So far, a monolithic,
simultaneous implementation of all elements demonstrating single-photon
operation remains elusive. Here, we present a fully-integrated Hanbury-Brown
and Twiss setup on a micron-sized footprint, consisting of a GaAs waveguide
embedding quantum dots as single-photon sources, a waveguide beamsplitter and
two superconducting nanowire single-photon detectors. This enables a
second-order correlation measurement at the single-photon level under both
continuous-wave and pulsed resonant excitation.
