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

arXiv:2406.07122 · Optics Express

Compact polarization-entangled photon source based on coexisting noncritically birefringent and quasi phase matching in a nonlinear crystal

Chun-Yao Yang, Chao-Yuan Wang, Kuan‐Heng Lin, Tsung-Ying Tsai, Chih-Chia Lin, Carlota Canalias, Li-Bang Wang, Atsushi Yabushita, Chih‐Sung Chuu

Published Jun 10, 2024• 1 citation
arXivHTMLPDF

Abstract

Polarization-entangled photons are indispensable to numerous quantum technologies and fundamental studies. In this paper, we propose and demonstrate what we believe to be a novel source that generates collinear polarization-entangled photons by simultaneously achieving two distinct types of phase-matching conditions (noncritically birefringent and quasi phase matching) in a periodically poled nonlinear crystal with a large poling period of 2 mm. The photon pairs are generated in a polarization-entangled state with a fidelity and concurrence of 0.998 and 0.935, respectively, and violate the Clauser-Horne-Shimony-Holt inequality by 84 standard deviations. The compact source does not require interferometer, delicate domain structures, or post selection, and is advantageous for scalable quantum computing and communication, where many replicas or chip-scale devices are needed.

DOI
10.1364/oe.527688

Related papers

Robust and bright polarization-entangled photon sources exploiting non-critical phase matching without periodic poling

Ilhwan Kim, Yosep Kim, Yong‐Su Kim +2 more

Entangled photon sources are essential for quantum information applications, including quantum computation, quantum communication, and quantum metrology. Periodically poled (PP) crystals are commonly used to generate bright photon sources through quasi-phase matching. However, fabricating uniform micron-scale periodic structures poses significant technical difficulties, typically limiting the crystal thickness to less than a millimeter. Here, we adopt non-critical phase matching to produce a robust and bright polarization-entangled photon source based on a bulk KTP crystal located in a Sagnac interferometer. This method is tolerant to variations in pump incidence angles and temperature, and theoretically offers about a 2.5-fold brightness enhancement compared to quasi-phase matching at a specific wavelength. Additionally, the absence of periodic poling allows for a larger crystal cross-section. Using a bulk KTP crystal without a PP structure, we experimentally produce the four Bell states with a brightness of 25.1 kHz/mW at a wavelength of 1079 nm, achieving purity, concurrence, and fidelity values close to 0.99. We believe our scheme will serve as a key building block for scalable and practical photonic quantum information applications.

arXiv:2409.07673•Optics Express•May 7, 2025•4 citations

Direct polarization-entangled photon pair generation using domain-engineered nonlinear crystals

Anatoly Shukhin, Inbar Hurvitz, Leonid Vidro +2 more

A biphoton polarization-frequency entanglement source was realized by shaping the phase-matching function of a periodically poled KTP crystal. It provides a simple method to achieve polarization (or spectral) entanglement in a simple collinear setup, based on single-pass SPDC and a dichroic (or polarizing) beam splitter. This is a robust and cost-effective configuration that can be easily implemented outside the laboratory environment. We characterized the source using two approaches: reconstructing the density matrix of the generated state with quantum state tomography, by recording the coincidences across 16 mutual polarization settings, in addition to a new method based on quantifying the symmetry of the joint spectral intensity by swapping between the signal and idler wavelengths. The polarization-entangled source violates the Clauser–Horne–Shimony–Holt inequality with a measured S =2.747±0.004. We also measured the polarization entanglement visibility in two mutually unbiased polarization bases and evaluated the squeezing level by characterizing the reduction in visibility at high pump power.

arXiv:2506.06460•Optica Quantum•Sep 3, 2025•8 citations

Non-collinear and non-degenerate polarization-entangled photon generation via concurrent type-I parametric downconversion in PPLN

Hugues Guillet de Chatellus, Alexander V. Sergienko, Bahaa E. A. Saleh +2 more

A periodically poled lithium niobate (PPLN) crystal has been used as an efficient source of non-collinearly generated polarization-entangled photon pairs at 810 and 1550 nm. The PPLN crystal was endowed with a specially designed poling pattern and the entangled photons were generated via the nonlinear optical process of spontaneous parametric down conversion (SPDC). A novel design based on overlapping two concurrent type-I quasi-phase-matching structures in a single PPLN crystals produced correlated pairs of alternatively polarized photons in largely separated spectral regions. The phase of the resulting two-photon state is directly linked to parameters of the nonlinear grating. Continuous tunability of the generated Bell state, from Phi(+) to Phi(-), has been demonstrated by translating a slightly wedged crystal perpendicular to the pump beam.

Optics Express•Oct 16, 2006•39 citations

Compact polarization-entangled source near 810 nm and its application to nonlocal retardance measurement

Shani Izhak, Inbar Hurvitz, H. S. Eisenberg +1 more

We present direct single-pass generation of polarization-entangled photon pairs near 810 nm in a domain-engineered nonlinear crystal pumped by a continuous-wave 405 nm laser. Despite operating outside the natural group-velocity matching regime, the source produces high-quality polarization entanglement with a Clauser–Horne–Shimony–Holt parameter of S =2.764±0.002. We further exploit the intrinsic phase sensitivity of the entangled state to perform nonlocal, wavelength-dependent retardance measurements of birefringent waveplates through two-photon polarization correlations. Our results establish a high-performance alternative to conventional polarization entanglement sources, combining room-temperature silicon-detector compatibility, compactness, and spectral flexibility, in a practical platform for phase-sensitive quantum metrology.

Optics Letters•May 19, 2026•0 citations

Broadband entangled photon source based on spatial multiplexing of single-pass, type-0 SPDC in bulk crystal

Milan Jana, swagata sarkar, Ayan Nai +1 more

We demonstrate a broadband entangled photon source based on a single-pass, type-0 phase-matched, non-collinear spontaneous parametric down-conversion (SPDC) process. By spatially multiplexing the intrinsically random transverse momentum states of biphotons emitted in an annular spatial distribution from a single-frequency-pumped, 2-mm-long periodically poled KTP crystal, we generate polarization-entangled pair photons with a spectral bandwidth of ∼130 nm centered at 810 nm. The negligible group-velocity mismatch of the co-polarized near-degenerate photons in single-pass and low birefringence of standard optical components preserves indistinguishability across the broadband emission without phase compensation, enabling high-quality polarization entanglement over the entire emission bandwidth. The source achieves a brightness of 0.57 Mpairs/s/mW and a two-photon coherence length of 6.97 μm, while exhibiting an interference visibility exceeding 95%, a Bell–CHSH parameter of 2.526 ± 0.005 that remains stable over 12 h of continuous operation and violates the Bell inequality by more than 100 standard deviations, and a state fidelity of 96.3%. The generic scheme providing the broadest bandwidth entangled biphotons at 810 nm, to our knowledge, can readily be used for other wavelengths as required for multiparty quantum networks and quantum sensing applications.

•Oct 27, 2026•0 citations

Robust, bright entangled photon source based on type-0, non-collinear phase-matching in periodically poled crystal

M. V. Jabir, G. K. Samanta

We demonstrate a novel source of high-brightness polarization entangled photons at room temperature. Using non-collinear phase-matching of PPKTP crystal we generate entangled state with 18.76kHz/mW/nm number of photon pairs, with fidelity ~0.975.

Frontiers in Optics•Jan 1, 2017•0 citations
Polarization-entangled photons are indispensable to numerous quantum technologies and fundamental studies. In this paper, we propose and demonstrate what we believe to be a novel source that generates collinear polarization-entangled photons by simultaneously achieving two distinct types of phase-matching conditions (noncritically birefringent and quasi phase matching) in a periodically poled nonlinear crystal with a large poling period of 2 mm. The photon pairs are generated in a polarization-entangled state with a fidelity and concurrence of 0.998 and 0.935, respectively, and violate the Clauser-Horne-Shimony-Holt inequality by 84 standard deviations. The compact source does not require interferometer, delicate domain structures, or post selection, and is advantageous for scalable quantum computing and communication, where many replicas or chip-scale devices are needed.
Entangled photon sources are essential for quantum information applications, including quantum computation, quantum communication, and quantum metrology. Periodically poled (PP) crystals are commonly used to generate bright photon sources through quasi-phase matching. However, fabricating uniform micron-scale periodic structures poses significant technical difficulties, typically limiting the crystal thickness to less than a millimeter. Here, we adopt non-critical phase matching to produce a robust and bright polarization-entangled photon source based on a bulk KTP crystal located in a Sagnac interferometer. This method is tolerant to variations in pump incidence angles and temperature, and theoretically offers about a 2.5-fold brightness enhancement compared to quasi-phase matching at a specific wavelength. Additionally, the absence of periodic poling allows for a larger crystal cross-section. Using a bulk KTP crystal without a PP structure, we experimentally produce the four Bell states with a brightness of 25.1 kHz/mW at a wavelength of 1079 nm, achieving purity, concurrence, and fidelity values close to 0.99. We believe our scheme will serve as a key building block for scalable and practical photonic quantum information applications.
A biphoton polarization-frequency entanglement source was realized by shaping the phase-matching function of a periodically poled KTP crystal. It provides a simple method to achieve polarization (or spectral) entanglement in a simple collinear setup, based on single-pass SPDC and a dichroic (or polarizing) beam splitter. This is a robust and cost-effective configuration that can be easily implemented outside the laboratory environment. We characterized the source using two approaches: reconstructing the density matrix of the generated state with quantum state tomography, by recording the coincidences across 16 mutual polarization settings, in addition to a new method based on quantifying the symmetry of the joint spectral intensity by swapping between the signal and idler wavelengths. The polarization-entangled source violates the Clauser–Horne–Shimony–Holt inequality with a measured S =2.747±0.004. We also measured the polarization entanglement visibility in two mutually unbiased polarization bases and evaluated the squeezing level by characterizing the reduction in visibility at high pump power.
A periodically poled lithium niobate (PPLN) crystal has been used as an efficient source of non-collinearly generated polarization-entangled photon pairs at 810 and 1550 nm. The PPLN crystal was endowed with a specially designed poling pattern and the entangled photons were generated via the nonlinear optical process of spontaneous parametric down conversion (SPDC). A novel design based on overlapping two concurrent type-I quasi-phase-matching structures in a single PPLN crystals produced correlated pairs of alternatively polarized photons in largely separated spectral regions. The phase of the resulting two-photon state is directly linked to parameters of the nonlinear grating. Continuous tunability of the generated Bell state, from Phi(+) to Phi(-), has been demonstrated by translating a slightly wedged crystal perpendicular to the pump beam.
We present direct single-pass generation of polarization-entangled photon pairs near 810 nm in a domain-engineered nonlinear crystal pumped by a continuous-wave 405 nm laser. Despite operating outside the natural group-velocity matching regime, the source produces high-quality polarization entanglement with a Clauser–Horne–Shimony–Holt parameter of S =2.764±0.002. We further exploit the intrinsic phase sensitivity of the entangled state to perform nonlocal, wavelength-dependent retardance measurements of birefringent waveplates through two-photon polarization correlations. Our results establish a high-performance alternative to conventional polarization entanglement sources, combining room-temperature silicon-detector compatibility, compactness, and spectral flexibility, in a practical platform for phase-sensitive quantum metrology.
We demonstrate a broadband entangled photon source based on a single-pass, type-0 phase-matched, non-collinear spontaneous parametric down-conversion (SPDC) process. By spatially multiplexing the intrinsically random transverse momentum states of biphotons emitted in an annular spatial distribution from a single-frequency-pumped, 2-mm-long periodically poled KTP crystal, we generate polarization-entangled pair photons with a spectral bandwidth of ∼130 nm centered at 810 nm. The negligible group-velocity mismatch of the co-polarized near-degenerate photons in single-pass and low birefringence of standard optical components preserves indistinguishability across the broadband emission without phase compensation, enabling high-quality polarization entanglement over the entire emission bandwidth. The source achieves a brightness of 0.57 Mpairs/s/mW and a two-photon coherence length of 6.97 μm, while exhibiting an interference visibility exceeding 95%, a Bell–CHSH parameter of 2.526 ± 0.005 that remains stable over 12 h of continuous operation and violates the Bell inequality by more than 100 standard deviations, and a state fidelity of 96.3%. The generic scheme providing the broadest bandwidth entangled biphotons at 810 nm, to our knowledge, can readily be used for other wavelengths as required for multiparty quantum networks and quantum sensing applications.