Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Photonics for Quantum (PfQ)

Portable integrated quantum optics for quantum communication

Tiphaine Kouadou, David Diaz, Paul G. Kwiat

Published Jul 19, 2023• 0 citations
Publisher

Abstract

We present integrated sources of polarization entanglement built on portable platforms for quantum communication. We employ type-II degenerate spontaneous parametric down conversion processes in PPKTP waveguides to generate pairs of orthogonally polarized photons at near-infrared wavelengths. The photons are sent to a 50/50 non-polarizing beam splitter (NPBS) to generate post-selected polarization-entangled states via coincidence measurements. The small size of the waveguides allows the installation of several units on the same platform, and thereby the generation of multiple entangled states simultaneously. We use a computer-controlled tomography system to characterize the produced states and combine the photons from adjacent waveguides on another NPBS to perform Bell-state measurements, a prerequisite to entanglement swapping. The overall experiment is compact and requires little alignment when set, making it an attractive option for local quantum networking using mobile platforms, e.g., drones or satellites.

DOI
10.1117/12.2680341

Related papers

Portable and integrated entanglement sources for quantum communication

Tiphaine Kouadou, Paul G. Kwiat

We present integrated sources of polarization entanglement built on portable platforms for quantum communication. We employ type-II degenerate spontaneous parametric down conversion processes in periodically poled potassium titanyl phosphate (PPKTP) waveguides to generate pairs of orthogonally polarized photons at near-infrared wavelengths. We use balanced non-polarizing beam splitter (NPBS) to generate post-selected polarization-entangled states via coincidence measurements and investigate the power and spectral tunability of the system. The small size of the waveguides allows the installation of several units on the same platform, and thereby the generation of multiple entangled states simultaneously. We built a separate platform containing a computer-controlled tomography system to characterize the produced states and another NPBS is installed to combine photons from adjacent waveguides and assess their interferability, a prerequisite to entanglement swapping. The overall experiment is compact and requires little alignment when set, making it an attractive option for local quantum networking using mobile platforms, e.g., drones or satellites.

Quantum Communications and Quantum Imaging•Oct 3, 2023•0 citations

Portable swappable polarization-entanglement sources

Tiphaine Kouadou, David Diaz, Paul G. Kwiat

We present a dual source of swappable entanglement in the near infrared for local quantum networking and free-space quantum links. Built on portable platforms, the polarization-entangled photons are generated via spontaneous parametric down conversion in two adjacent fiber-pigtailed type-II PPKTP waveguides.

Quantum 2.0 Conference and Exhibition•Jan 1, 2023•0 citations

Compact entanglement sources for portable quantum information platforms

Tiphaine Kouadou, Colin P. Lualdi, Spencer J. Johnson +6 more

We discuss two novel entanglement sources utilizing spontaneous parametric downconversion in periodically poled waveguides. Using quasi-phase matched KTP crystals, we have demonstrated a post-selection-based polarization entangled degenerate source at 810 nm, as well as a post-selection-free non-degenerate collinear source producing entangled photons at 810 nm and 1550 nm. The sources exhibit high brightness and state quality – with the non-degenerate source achieving fidelities and purities up to 99% – with clear paths for further improvement. Furthermore, they are compact, stable, and need little alignment when set, critical for practical quantum communication and network applications. Lastly, their small size, weight, and power (SWaP) makes them an attractive option for mobile platforms, e.g., with drones or satellites.

Quantum Computing, Communication, and Simulation•Mar 2, 2022•1 citation

Integrated polarization-entangled photon source for wavelength-multiplexed quantum networks

Xiaodong Shi, Yue Li, Jinyi Du +13 more

Entangled photons are fundamental resources for quantum communication, computing, and networking. Among them, polarization-entangled photon pairs play an important role due to their straightforward state manipulation and direct use in quantum key distribution, teleportation, and network protocols. However, realizing compact, efficient, and scalable polarization-entangled sources that meet the requirements of practical deployment remains a major challenge. Here, we present a simple yet high-performance on-chip polarization-entangled photon-pair source on thin-film lithium niobate (TFLN). Our device employs dual quasi-phase matching (D-QPM) that sequentially supports type-0 and type-I spontaneous parametric down-conversion in a single nanophotonic waveguide, eliminating the need for interferometers, polarization rotators, or other complex circuits. The source directly produces high-fidelity Bell states with broad bandwidth, high brightness, and low noise. Using this integrated platform, we realize wavelength-multiplexed entanglement distribution in a four-user quantum network deployed over metropolitan fiber links up to 50 km. These results establish a robust and scalable pathway toward practical quantum communication systems and multi-user quantum mesh networks based on integrated photonics.

physics.opticsCross-listedarXiv:2511.22680•Nature Communications•Nov 28, 2025•1 citation

Towards nondegenerate polarization entanglement from a waveguide down-conversion source

Kristina A. Meier, Fumihiro Kaneda, Paul G. Kwiat

As optical quantum information processing protocols and experiments become increasingly more complex, integrated optics provide a small and robust alternative to traditional bulk optics. Specifically, waveguide technology allows for the creation of bright single-photon sources based on the fact that photon pairs can be created at any location along the waveguide. For our goals, we are working on the characterization of a highly nondegenerate Spontaneous Parametric Down-Conversion (SPDC) waveguide source on a periodically poled KTP (PPKTP) crystal. Our current waveguide source uses type-II phase-matching to create collinear signal and idler photons at 1550 nm and 810 nm, respectively, with the promise of generating simultaneous time-bin and polarization entanglement in future iterations. Our intended source application is for use in quantum key distribution and superdense teleportation protocols between a space platform and collection telescopes on Earth.

Advanced Photon Counting Techniques•May 14, 2018•2 citations

Broadband Telecom Entanglement from an All-Fiber Type-0 Sagnac Source

Alessandro Cestelli, Spyridon Grountas, Scott Mc Haffie +3 more

We demonstrate a compact, practical all-fiber source of non-degenerate telecom-band polarization-entangled photon pairs assembled from off-the-shelf components. The compact fiber-integrated architecture is designed to be affordable, straightforward to assemble and align, and compatible with existing optical-fiber infrastructure. Photon pairs are generated through type-0 spontaneous parametric down-conversion in a pigtailed periodically poled lithium-niobate waveguide embedded in a Sagnac interferometer. At 0.5 mW pump power, quantum-state tomography yields a Bell-state fidelity $F_{Φ^-}=0.850$, purity $P=0.836$, and concurrence $C=0.782$. A separate CHSH measurement gives $S=2.3301\pm0.0075$. The measured Bell-state fidelity is sufficient for the reconstructed polarization state to support qubit teleportation above the classical fidelity limit under ideal protocol operations. Analysis of the density matrix shows that approximately 96.7% of the population remains in the desired $|HH\rangle$-$|VV\rangle$ subspace, with a normalized coherence of approximately 0.86. A residual relative-phase offset indicates that local phase compensation could increase the Bell-state fidelity to approximately 0.8865. We further characterize the brightness--quality trade-off and obtain a corrected pair-rate slope of $(0.918\pm0.040)$ Mcps mW$^{-1}$. The broadband emission and fiber interfaces offer a route to multiuser entanglement distribution through off-the-shelf multichannel wavelength-division multiplexers with passbands matched to the signal and idler wavelengths.

quant-pharXiv:2610.08025•Oct 7, 2026•0 citations
We present integrated sources of polarization entanglement built on portable platforms for quantum communication. We employ type-II degenerate spontaneous parametric down conversion processes in PPKTP waveguides to generate pairs of orthogonally polarized photons at near-infrared wavelengths. The photons are sent to a 50/50 non-polarizing beam splitter (NPBS) to generate post-selected polarization-entangled states via coincidence measurements. The small size of the waveguides allows the installation of several units on the same platform, and thereby the generation of multiple entangled states simultaneously. We use a computer-controlled tomography system to characterize the produced states and combine the photons from adjacent waveguides on another NPBS to perform Bell-state measurements, a prerequisite to entanglement swapping. The overall experiment is compact and requires little alignment when set, making it an attractive option for local quantum networking using mobile platforms, e.g., drones or satellites.
We present integrated sources of polarization entanglement built on portable platforms for quantum communication. We employ type-II degenerate spontaneous parametric down conversion processes in periodically poled potassium titanyl phosphate (PPKTP) waveguides to generate pairs of orthogonally polarized photons at near-infrared wavelengths. We use balanced non-polarizing beam splitter (NPBS) to generate post-selected polarization-entangled states via coincidence measurements and investigate the power and spectral tunability of the system. The small size of the waveguides allows the installation of several units on the same platform, and thereby the generation of multiple entangled states simultaneously. We built a separate platform containing a computer-controlled tomography system to characterize the produced states and another NPBS is installed to combine photons from adjacent waveguides and assess their interferability, a prerequisite to entanglement swapping. The overall experiment is compact and requires little alignment when set, making it an attractive option for local quantum networking using mobile platforms, e.g., drones or satellites.
We discuss two novel entanglement sources utilizing spontaneous parametric downconversion in periodically poled waveguides. Using quasi-phase matched KTP crystals, we have demonstrated a post-selection-based polarization entangled degenerate source at 810 nm, as well as a post-selection-free non-degenerate collinear source producing entangled photons at 810 nm and 1550 nm. The sources exhibit high brightness and state quality – with the non-degenerate source achieving fidelities and purities up to 99% – with clear paths for further improvement. Furthermore, they are compact, stable, and need little alignment when set, critical for practical quantum communication and network applications. Lastly, their small size, weight, and power (SWaP) makes them an attractive option for mobile platforms, e.g., with drones or satellites.
Entangled photons are fundamental resources for quantum communication, computing, and networking. Among them, polarization-entangled photon pairs play an important role due to their straightforward state manipulation and direct use in quantum key distribution, teleportation, and network protocols. However, realizing compact, efficient, and scalable polarization-entangled sources that meet the requirements of practical deployment remains a major challenge. Here, we present a simple yet high-performance on-chip polarization-entangled photon-pair source on thin-film lithium niobate (TFLN). Our device employs dual quasi-phase matching (D-QPM) that sequentially supports type-0 and type-I spontaneous parametric down-conversion in a single nanophotonic waveguide, eliminating the need for interferometers, polarization rotators, or other complex circuits. The source directly produces high-fidelity Bell states with broad bandwidth, high brightness, and low noise. Using this integrated platform, we realize wavelength-multiplexed entanglement distribution in a four-user quantum network deployed over metropolitan fiber links up to 50 km. These results establish a robust and scalable pathway toward practical quantum communication systems and multi-user quantum mesh networks based on integrated photonics.
As optical quantum information processing protocols and experiments become increasingly more complex, integrated optics provide a small and robust alternative to traditional bulk optics. Specifically, waveguide technology allows for the creation of bright single-photon sources based on the fact that photon pairs can be created at any location along the waveguide. For our goals, we are working on the characterization of a highly nondegenerate Spontaneous Parametric Down-Conversion (SPDC) waveguide source on a periodically poled KTP (PPKTP) crystal. Our current waveguide source uses type-II phase-matching to create collinear signal and idler photons at 1550 nm and 810 nm, respectively, with the promise of generating simultaneous time-bin and polarization entanglement in future iterations. Our intended source application is for use in quantum key distribution and superdense teleportation protocols between a space platform and collection telescopes on Earth.
We demonstrate a compact, practical all-fiber source of non-degenerate telecom-band polarization-entangled photon pairs assembled from off-the-shelf components. The compact fiber-integrated architecture is designed to be affordable, straightforward to assemble and align, and compatible with existing optical-fiber infrastructure. Photon pairs are generated through type-0 spontaneous parametric down-conversion in a pigtailed periodically poled lithium-niobate waveguide embedded in a Sagnac interferometer. At 0.5 mW pump power, quantum-state tomography yields a Bell-state fidelity FΦ−=0.850F_{Φ^-}=0.850FΦ−​=0.850, purity P=0.836P=0.836P=0.836, and concurrence C=0.782C=0.782C=0.782. A separate CHSH measurement gives S=2.3301±0.0075S=2.3301\pm0.0075S=2.3301±0.0075. The measured Bell-state fidelity is sufficient for the reconstructed polarization state to support qubit teleportation above the classical fidelity limit under ideal protocol operations. Analysis of the density matrix shows that approximately 96.7% of the population remains in the desired ∣HH⟩|HH\rangle∣HH⟩-∣VV⟩|VV\rangle∣VV⟩ subspace, with a normalized coherence of approximately 0.86. A residual relative-phase offset indicates that local phase compensation could increase the Bell-state fidelity to approximately 0.8865. We further characterize the brightness--quality trade-off and obtain a corrected pair-rate slope of (0.918±0.040)(0.918\pm0.040)(0.918±0.040) Mcps mW−1^{-1}−1. The broadband emission and fiber interfaces offer a route to multiuser entanglement distribution through off-the-shelf multichannel wavelength-division multiplexers with passbands matched to the signal and idler wavelengths.