On-chip generation of hybrid polarization-frequency entangled biphoton states

We demonstrate a chip-integrated semiconductor source that combines polarization and frequency entanglement, allowing the generation of entangled biphoton states in a hybrid degree of freedom without post-manipulation. Our AlGaAs device is based on type-II spontaneous parametric downconversion in a counterpropagating phasematching scheme in which the modal birefringence lifts the degeneracy between the two possible nonlinear interactions. This allows the direct generation of polarization-frequency entangled photons at room temperature and telecom wavelength, and in two distinct spatial modes, offering enhanced flexibility for quantum information protocols. The state entanglement is quantified by a combined measurement of the joint spectrum and Hong-Ou-Mandel interference (raw visibility 70.1% & PLUSMN; 1.1%) of the biphotons, allowing to reconstruct a restricted density matrix in the hybrid polarization-frequency space. & COPY; 2023 Chinese Laser Press

Automated summary

We demonstrate a chip-integrated semiconductor source that combines polarization and frequency entanglement, allowing the generation of entangled biphoton states in a hybrid degree of freedom without post-manipulation. The device is based on type-II spontaneous parametric downconversion in a counterpropagating phasematching scheme, enabling the direct generation of polarization-frequency entangled photons at room temperature and telecom wavelength. The state entanglement is quantified by a combined measurement of the joint spectrum and Hong-Ou-Mandel interference.