Entangled photon pairs are crucial resources for quantum information processing protocols.Via the process of spontaneous parametric downconversion(SPDC),we can generate these photon pairs using bulk nonlinear crystals...Entangled photon pairs are crucial resources for quantum information processing protocols.Via the process of spontaneous parametric downconversion(SPDC),we can generate these photon pairs using bulk nonlinear crystals.Traditionally,the crystal is designed to satisfy a specific type of phase-matching condition.Here,we report controllable transitions among different types of phase matching in a single periodically poled potassium titanyl phosphate crystal.By carefully selecting pump conditions,we can satisfy different phase-matching conditions.This allows us to observe first-order Type-II,fifth-order Type-I,third-order Type-0,and fifth-order Type-II SPDCs.The temperature-dependent spectra of our source were also analyzed in detail.Finally,we discussed the possibility of observing more than nine SPDCs in this crystal.Our work not only deepens the understanding of the physics behind phase-matching conditions,but also offers the potential for a highly versatile entangled biphoton source for quantum information research.展开更多
Reliable generation of single photons is of key importance for fundamental physical experiments and quantum protocols.The periodically poled lithium niobate[LN]waveguide has shown promise for an integrated quantum sou...Reliable generation of single photons is of key importance for fundamental physical experiments and quantum protocols.The periodically poled lithium niobate[LN]waveguide has shown promise for an integrated quantum source due to its large spectral tunability and high efficiency,benefiting from the quasi-phase-matching.Here we demonstrate photon-pair sources based on an LN waveguide periodically poled by a tightly focused femtosecond laser beam.The pair coincidence rate reaches~8000 counts per second for average pump power of 3.2 m W[peak power is 2.9 k W).Our results prove the possibility of application of the nonlinear photonics structure fabricated by femtosecond laser to the integrated quantum source.This method can be extended to three-dimensional domain structures,which provide a potential platform for steering the spatial degree of freedom of the entangled two-photon states.展开更多
The two-photon state with spatial entanglement is an essential resource for testing fundamental laws of quantum mechanics and various quantum applications.Its creation typically relies on spontaneous parametric downco...The two-photon state with spatial entanglement is an essential resource for testing fundamental laws of quantum mechanics and various quantum applications.Its creation typically relies on spontaneous parametric downconversion in bulky nonlinear crystals where the tunability of spatial entanglement is limited.Here,we predict that ultrathin nonlinear lithium niobate metasurfaces can generate and diversely tune spatially entangled photon pairs.The spatial properties of photons including the emission pattern,rate,and degree of spatial entanglement are analyzed theoretically with the coupled mode theory and Schmidt decomposition method.We show that by leveraging the strong angular dispersion of the metasurface,the degree of spatial entanglement quantified by the Schmidt number can be decreased or increased by changing the pump laser wavelength and a Gaussian beam size.This flexibility can facilitate diverse quantum applications of entangled photon states generated from nonlinear metasurfaces.展开更多
基金supported by the National Natural Science Foundation of China(Nos.12074299,11704290,and 92365106)the Guangdong Provincial Key Laboratory(No.GKLQSE202102)the Natural Science Foundation of Hubei Province(2022CFA039)。
文摘Entangled photon pairs are crucial resources for quantum information processing protocols.Via the process of spontaneous parametric downconversion(SPDC),we can generate these photon pairs using bulk nonlinear crystals.Traditionally,the crystal is designed to satisfy a specific type of phase-matching condition.Here,we report controllable transitions among different types of phase matching in a single periodically poled potassium titanyl phosphate crystal.By carefully selecting pump conditions,we can satisfy different phase-matching conditions.This allows us to observe first-order Type-II,fifth-order Type-I,third-order Type-0,and fifth-order Type-II SPDCs.The temperature-dependent spectra of our source were also analyzed in detail.Finally,we discussed the possibility of observing more than nine SPDCs in this crystal.Our work not only deepens the understanding of the physics behind phase-matching conditions,but also offers the potential for a highly versatile entangled biphoton source for quantum information research.
基金supported financially by the National Key R&D Program of China(Nos.2019YFA0705000,2017YFA0303800,2017YFA0303700,2019YFA0308700,and 2020YFA0309500)the National Natural Science Foundation of China(Nos.12074197,12074196,11774183,and 11922406)。
文摘Reliable generation of single photons is of key importance for fundamental physical experiments and quantum protocols.The periodically poled lithium niobate[LN]waveguide has shown promise for an integrated quantum source due to its large spectral tunability and high efficiency,benefiting from the quasi-phase-matching.Here we demonstrate photon-pair sources based on an LN waveguide periodically poled by a tightly focused femtosecond laser beam.The pair coincidence rate reaches~8000 counts per second for average pump power of 3.2 m W[peak power is 2.9 k W).Our results prove the possibility of application of the nonlinear photonics structure fabricated by femtosecond laser to the integrated quantum source.This method can be extended to three-dimensional domain structures,which provide a potential platform for steering the spatial degree of freedom of the entangled two-photon states.
基金supported by the Australian Research Council(DP190101559,CE200100010).
文摘The two-photon state with spatial entanglement is an essential resource for testing fundamental laws of quantum mechanics and various quantum applications.Its creation typically relies on spontaneous parametric downconversion in bulky nonlinear crystals where the tunability of spatial entanglement is limited.Here,we predict that ultrathin nonlinear lithium niobate metasurfaces can generate and diversely tune spatially entangled photon pairs.The spatial properties of photons including the emission pattern,rate,and degree of spatial entanglement are analyzed theoretically with the coupled mode theory and Schmidt decomposition method.We show that by leveraging the strong angular dispersion of the metasurface,the degree of spatial entanglement quantified by the Schmidt number can be decreased or increased by changing the pump laser wavelength and a Gaussian beam size.This flexibility can facilitate diverse quantum applications of entangled photon states generated from nonlinear metasurfaces.
