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arXiv:2304.14245 · Optics Letters

Discrete frequency-bin entanglement generation via cascaded second-order nonlinear processes in Sagnac interferometer

Jiarui Li, Chenzhi Yuan, Si Shen, Zichang Zhang, Ruiming Zhang, Hao Li, You Wang, Guangwei Deng, Lixing You, Zhen Wang, Hai‐Zhi Song, Yunru Fan, Guang‐Can Guo, Qiang Zhou

Published Apr 27, 2023• 10 citations
arXivHTMLPDF

Abstract

Discrete frequency-bin entanglement is an essential resource for applications in quantum information processing. In this Letter, we propose and demonstrate a scheme to generate discrete frequency-bin entanglement with a single piece of periodically poled lithium niobate waveguide in a modified Sagnac interferometer. Correlated two-photon states in both directions of the Sagnac interferometer are generated through cascaded second-order optical nonlinear processes. A relative phase difference between the two states is introduced by changing the polarization state of pump light, thus manipulating the two-photon state at the output of the Sagnac interferometer. The generated two-photon state is sent into a fiber polarization splitter, and then a pure discrete frequency-bin entangled two-photon state is obtained by setting the pump light. The frequency entanglement property is measured by a spatial quantum beating with a visibility of 96.0±6.1%. The density matrix is further obtained with a fidelity of 98.0±3.0% to the ideal state. Our demonstration provides a promising method for the generation of pure discrete frequency-bin entanglement at the telecom band, which is desired in quantum photonics.

DOI
10.1364/ol.489656

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Discrete frequency-bin entanglement is an essential resource for applications in quantum information processing. In this Letter, we propose and demonstrate a scheme to generate discrete frequency-bin entanglement with a single piece of periodically poled lithium niobate waveguide in a modified Sagnac interferometer. Correlated two-photon states in both directions of the Sagnac interferometer are generated through cascaded second-order optical nonlinear processes. A relative phase difference between the two states is introduced by changing the polarization state of pump light, thus manipulating the two-photon state at the output of the Sagnac interferometer. The generated two-photon state is sent into a fiber polarization splitter, and then a pure discrete frequency-bin entangled two-photon state is obtained by setting the pump light. The frequency entanglement property is measured by a spatial quantum beating with a visibility of 96.0±6.1%. The density matrix is further obtained with a fidelity of 98.0±3.0% to the ideal state. Our demonstration provides a promising method for the generation of pure discrete frequency-bin entanglement at the telecom band, which is desired in quantum photonics.
By using cascaded second-order nonlinear optical processes in a piece of periodically poled lithium niobate waveguide, we generate 1.5 μ\muμ m discrete frequency-bin entangled two-photon state with a spatial quantum beating visibility of 93.0 ± 5.2%.
In this work, we propose and demonstrate the frequency-bin entangled two-photon state via cascaded second harmonic generation and spontaneous parametric down conversion (SHG-SPDC) processes in a single piece of PPLN waveguide. Our scheme is based on all fiber-pigtailed components at 1.5 μm telecom band. Two frequency-bins at 1531.34 nm and 1548.91 nm with bandwidth of 1.04 nm are prepared to be entangled. The frequency entanglement property of our generated two-photon states is measured by spatial two-photon quantum beating. A two-photon beating curve with a visibility of 87.92±0.47% is obtained, showing a good property of frequency-bin entanglement.
Entangled photon pairs are one of the most important resources for the development of quantum communication technologies. In order to produce pulsed photon pairs in the telecommunication band from 1.5 mum pump light, most of the previous experiments used two successive periodically poled lithium niobate (PPLN) waveguides. We report what we believe to be a new method using cascaded second-order nonlinearity in a single PPLN waveguide to produce high-purity time-bin entangled photon pairs. We confirmed the generation of entanglement through a two-photon interference experiment showing a coincidence fringe with a visibility of up to 97%.
In this Letter, the generation of a 1.5 μm discrete frequency-entangled two-photon state is realized based on a piece of commercial polarization-maintaining fiber (PMF). It is connected with a polarization beam splitter to realize a modified Sagnac fiber loop (MSFL). Correlated two-photon states are generated through a spontaneous four-wave-mixing process along the two propagation directions of the MSFL, and output from the MSFL with orthogonal polarizations. Their quantum interference is realized through a 45° polarization collimation between polarization axes of PMFs inside and outside the MSFL, while their phase difference is controlled by the polarization state of the pump light. The frequency-entangled property of the two-photon state is demonstrated by a spatial quantum beating experiment with a fringe visibility of 98.2±1.3%, without subtracting the accidental coincidence counts. The proposed scheme generates a 1.5 μm discrete frequency-entangled two-photon state in a polarization-maintaining way, which is desired in practical quantum light sources.
Abstract In this paper, we demonstrate the generation of high-performance entangled photon-pairs in different degrees of freedom from a single piece of fiber pigtailed periodically poled LiNbO 3 (PPLN) waveguide. We utilize cascaded second-order nonlinear optical processes, i.e., second-harmonic generation (SHG) and spontaneous parametric downconversion (SPDC), to generate photon-pairs. Previously, the performance of the photon-pairs is contaminated by Raman noise photons. Here by fiber-integrating the PPLN waveguide with noise-rejecting filters, we obtain a coincidence-to-accidental ratio (CAR) higher than 52,600 with photon-pair generation and detection rate of 52.36 kHz and 3.51 kHz, respectively. Energy-time, frequency-bin, and time-bin entanglement is prepared by coherently superposing correlated two-photon states in these degrees of freedom, respectively. The energy-time entangled two-photon states achieve the maximum value of CHSH-Bell inequality of S = 2.71 ± 0.02 with two-photon interference visibility of 95.74 ± 0.86%. The frequency-bin entangled two-photon states achieve fidelity of 97.56 ± 1.79% with a spatial quantum beating visibility of 96.85 ± 2.46%. The time-bin entangled two-photon states achieve the maximum value of CHSH-Bell inequality of S = 2.60 ± 0.04 and quantum tomographic fidelity of 89.07 ± 4.35%. Our results provide a potential candidate for the quantum light source in quantum photonics.