Temporally ultralong biphotons with a linewidth of 50 kHz

I. INTRODUCTION

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ChooseTop of pageABSTRACTI. INTRODUCTION <<II. EXPERIMENTAL SETUPIII. THEORETICAL MODELIV. RESULTS AND DISCUSSIO...V. CONCLUSIONREFERENCESPrevious sectionNext sectionSources of biphotons or pairs of time-correlated single photons are widely utilized in quantum information research and applications. While one of the paired photons is detected to trigger, or start, a quantum operation, the other will be used in the operation as a heralded single photon or, if carrying a wave function or quantum state, a heralded qubit. Biphotons are produced mainly via two kinds of schemes: spontaneous parametric down conversion (SPDC) and spontaneous four-wave mixing (SFWM). A SPDC biphoton source is commonly made of a nonlinear crystal placed inside an optical cavity.1–101. X.-H. Bao, Y. Qian, J. Yang, H. Zhang, Z.-B. Chen, T. Yang, and J.-W. Pan, “Generation of narrow-band polarization-entangled photon pairs for atomic quantum memories,” Phys. Rev. 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Zhang, “Sub-megahertz narrow-band photon pairs at 606 nm for solid-state quantum memories,” APL Photonics 5, 066105 (2020). https://doi.org/10.1063/5.0006021 A SFWM biphoton source generally consists of a cold atom cloud,11–1711. L. Zhao, X. Guo, C. Liu, Y. Sun, M. M. T. Loy, and S. Du, “Photon pairs with coherence time exceeding 1 μs,” Optica 1, 84–88 (2014). https://doi.org/10.1364/optica.1.00008412. Z. Han, P. Qian, L. Zhou, J. F. Chen, and W. Zhang, “Coherence time limit of the biphotons generated in a dense cold atom cloud,” Sci. Rep. 5, 9126 (2015). https://doi.org/10.1038/srep0912613. L. Zhao, Y. Su, and S. Du, “Narrowband biphoton generation in the group delay regime,” Phys. Rev. A 93, 033815 (2016). https://doi.org/10.1103/physreva.93.03381514. P. Farrera, G. Heinze, B. Albrecht, M. Ho, M. Chávez, C. Teo, N. Sangouard, and H. de Riedmatten, “Generation of single photons with highly tunable wave shape from a cold atomic ensemble,” Nat. 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White, “Sub-megahertz linewidth single photon source,” APL Photonics 1, 096101 (2016); https://doi.org/10.1063/1.4966915Erratum 2, 119901 (2017). https://doi.org/10.1063/1.5005838 and Liu et al. demonstrated a biphoton source with a linewidth of 265 kHz.1010. J. Liu, J. Liu, P. Yu, and G. Zhang, “Sub-megahertz narrow-band photon pairs at 606 nm for solid-state quantum memories,” APL Photonics 5, 066105 (2020). https://doi.org/10.1063/5.0006021 Both sources produced multi-mode biphotons, and the frequency modes of the biphotons spanned several hundreds of MHz. Although SPDC biphoton sources can generate single-mode biphotons, currently all of these single-mode biphotons have linewidths larger than 1 MHz, e.g., Refs. 5–75. D. Rieländer, A. Lenhard, M. Mazzera, and H. de Riedmatten, “Cavity enhanced telecom heralded single photons for spin-wave solid state quantum memories,” New J. Phys. 18, 123013 (2016). https://doi.org/10.1088/1367-2630/aa4f386. C.-H. Wu, T.-Y. Wu, Y.-C. Yeh, P.-H. 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Du, “Narrowband biphoton generation in the group delay regime,” Phys. Rev. A 93, 033815 (2016). https://doi.org/10.1103/physreva.93.033815 Using an atomic vapor heated to 38 °C in the EIT-based SFWM process, Hsu et al. generated biphotons with a linewidth of 320 kHz.22,2422. C.-Y. Hsu, Y.-S. Wang, J.-M. Chen, F.-C. Huang, Y.-T. Ke, E. K. Huang, W. Hung, K.-L. Chao, S.-S. Hsiao, Y.-H. Chen, C.-S. Chuu, Y.-C. Chen, Y.-F. Chen, and I. A. Yu, “Generation of sub-MHz and spectrally-bright biphotons from hot atomic vapors with a phase mismatch-free scheme,” Opt. Express 29, 4632 (2021). https://doi.org/10.1364/oe.41547324. J.-M. Chen, C.-Y. Hsu, W.-K. Huang, S.-S. Hsiao, F.-C. Huang, Y.-H. Chen, C.-S. Chuu, Y.-C. Chen, Y.-F. Chen, and I. A. Yu, “Room-temperature biphoton source with a spectral brightness near the ultimate limit,” Phys. Rev. Res. 4, 023132 (2022). https://doi.org/10.1103/physrevresearch.4.023132 Among all the biphoton sources of integrated photonics devices, the narrowest linewidth was 92 MHz.3737. T. J. Steiner, J. E. Castro, L. Chang, Q. Dang, W. Xie, J. Norman, J. E. Bowers, and G. Moody, “Ultrabright entangled-photon-pair generation from an AlGaAs-on-insulator microring resonator,” PRX Quantum 2, 010337 (2021). https://doi.org/10.1103/prxquantum.2.010337 There has been no report on the biphoton source with a linewidth below 100 kHz until now. Please see Table I for the list of all biphoton sources with linewidths below 1 MHz.Table icon

TABLE I. Biphoton sources with spectral profiles of the full width at the half maximum (FWHM) below 1 MHz.

ProcessMediumTypeaTemporal FWHM (μs)Spectral FWHM (kHz)gs,as(2)(0)ReferencesSPDCNonlinear crystalMM0.33c430d5.244. M. Rambach, A. Nikolova, T. J. Weinhold, and A. G. White, “Sub-megahertz linewidth single photon source,” APL Photonics 1, 096101 (2016); https://doi.org/10.1063/1.4966915Erratum 2, 119901 (2017). https://doi.org/10.1063/1.5005838SPDCNonlinear crystalMM0.83c265d3.91010. J. Liu, J. Liu, P. Yu, and G. Zhang, “Sub-megahertz narrow-band photon pairs at 606 nm for solid-state quantum memories,” APL Photonics 5, 066105 (2020). https://doi.org/10.1063/5.0006021SFWMCold atom cloudSM1.7430111111. L. Zhao, X. Guo, C. Liu, Y. Sun, M. M. T. Loy, and S. Du, “Photon pairs with coherence time exceeding 1 μs,” Optica 1, 84–88 (2014). https://doi.org/10.1364/optica.1.000084SFWMCold atom cloudSM2.13806.81212. Z. Han, P. Qian, L. Zhou, J. F. Chen, and W. Zhang, “Coherence time limit of the biphotons generated in a dense cold atom cloud,” Sci. Rep. 5, 9126 (2015). https://doi.org/10.1038/srep09126SFWMCold atom cloudSM2.92506.11313. L. Zhao, Y. Su, and S. Du, “Narrowband biphoton generation in the group delay regime,” Phys. Rev. A 93, 033815 (2016). https://doi.org/10.1103/physreva.93.033815SFWMCold atom cloudSM13.4504.4This workSFWMHot atomic vaporSM0.663206.42222. C.-Y. Hsu, Y.-S. Wang, J.-M. Chen, F.-C. Huang, Y.-T. Ke, E. K. Huang, W. Hung, K.-L. Chao, S.-S. Hsiao, Y.-H. Chen, C.-S. Chuu, Y.-C. Chen, Y.-F. Chen, and I. A. Yu, “Generation of sub-MHz and spectrally-bright biphotons from hot atomic vapors with a phase mismatch-free scheme,” Opt. Express 29, 4632 (2021). https://doi.org/10.1364/oe.415473 and 2424. J.-M. Chen, C.-Y. Hsu, W.-K. Huang, S.-S. Hsiao, F.-C. Huang, Y.-H. Chen, C.-S. Chuu, Y.-C. Chen, Y.-F. Chen, and I. A. Yu, “Room-temperature biphoton source with a spectral brightness near the ultimate limit,” Phys. Rev. Res. 4, 023132 (2022). https://doi.org/10.1103/physrevresearch.4.023132

Here, we report a cold-atom SFWM source of biphotons with a tunable temporal width. A novel scheme for the arrangement of classical fields’ and biphotons’ propagation directions was used in the experiment. The scheme not only maintains a nearly phase-mismatch-free condition but also effectively reduces classical light’s leakages to the single-photon counting modules (SPCMs). Consequently, while maintaining non-classicality, the biphotons had a temporal width as long as 13.4 µs or a spectral linewidth as narrow as 50 kHz. A large optical depth (OD) as well as a negligible decoherence rate in the experimental system enabled the propagation delay time of the EIT effect to dominate the temporal profile of the biphoton wave packet. Furthermore, we were able to tune the temporal or, equivalently, spectral width by about 24 folds, and at the same time, the change in the generation rate of the biphoton source was less than 15%. A generation rate per pump power per linewidth of 1.2 × 106 pairs/(s mW MHz) was achieved at the temporal width of 13.4 µs. In quantum operations, this biphoton source can meet any harsh requirements of linewidth.

II. EXPERIMENTAL SETUP

Section:

ChooseTop of pageABSTRACTI. INTRODUCTIONII. EXPERIMENTAL SETUP <<III. THEORETICAL MODELIV. RESULTS AND DISCUSSIO...V. CONCLUSIONREFERENCESPrevious section

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