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Acta Physica Sinica

Preparation of spectrally pure single-photon source at 3 μm mid-infrared band from lithium niobate crystal with domain sequence algorithm

Chen-Tao Zhang, Xiao-Tao Shi, Wen-Xin Zhu, Jin-Long Zhu, Xiangying Hao, Rui‐Bo Jin

Published Jan 1, 2022• 4 citations
Publisher

Abstract

The single-photon source in mid-infrared (MIR) band is very important for the next generation of quantum sensing, quantum communication and quantum imaging. At present, the commonly used method of generating MIR single-photon source is based on the spontaneous parametric down conversion (SPDC) process in the periodically poled lithium niobate (PPLN) crystal. However, the spectral purity of single-photon source based on the ordinary PPLN is not high, specifically, its maximum value is only about 0.82, which affects the fidelity of quantum information processing scheme. In this paper, 4000 polarized domains in a 30-mm-long LN crystal are customized by using the domain design theory. The sidelobes in the phase matching function are eliminated, and the Gaussian distribution is obtained. The calculated spectral purity of the single-photon source can reach 0.99, and its tunable range is 2.7–3.3 μm. The customized poled lithium niobate (CPLN) is expected to provide a single-photon source with excellent performance for the study of quantum information in the MIR band.

DOI
10.7498/aps.71.20220739

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The single-photon source in mid-infrared (MIR) band is very important for the next generation of quantum sensing, quantum communication and quantum imaging. At present, the commonly used method of generating MIR single-photon source is based on the spontaneous parametric down conversion (SPDC) process in the periodically poled lithium niobate (PPLN) crystal. However, the spectral purity of single-photon source based on the ordinary PPLN is not high, specifically, its maximum value is only about 0.82, which affects the fidelity of quantum information processing scheme. In this paper, 4000 polarized domains in a 30-mm-long LN crystal are customized by using the domain design theory. The sidelobes in the phase matching function are eliminated, and the Gaussian distribution is obtained. The calculated spectral purity of the single-photon source can reach 0.99, and its tunable range is 2.7–3.3 μm. The customized poled lithium niobate (CPLN) is expected to provide a single-photon source with excellent performance for the study of quantum information in the MIR band.
By utilizing the extended phase-matching (EPM) method, we investigate the generation of single photons with high spectral-purity in a magnesium-doped periodically-poled lithium niobate (MgO:PPLN) crystal via the spontaneous parametric down-conversion (SPDC) process. By adjusting the temperature and pump wavelength, the wavelength of the single photons can be tuned from telecom to mid-infrared (MIR) wavelengths, for which the spectral-purity can be above 0.95 with high transmission filters. In experiments, we engineer a MgO:PPLN with poling period of 20.35 μm which emits the EPM photon pair centered at 1496.6 nm and 1644.0 nm and carry out the joint spectral intensity (JSI) and Glauber’s second-order self-correlation measurements to characterize the spectral purity. The results are in good agreement with the numerical simulations. Our work may provide a valuable approach for the generation of spectrally pure single photons at a wide range of wavelengths which is competent for various photonic quantum technologies.
Abstract Quantum light sources in the mid‐infrared (MIR) band play an important role in many applications, such as quantum sensing, quantum imaging, and quantum communication. However, there is still a lack of high‐quality quantum light sources in the MIR band, such as the spectrally pure single‐photon source. In this work, the generation of a spectrally‐pure state in an optimized poled lithium niobate crystal using a metaheuristic algorithm is presented. In particular, the particle swarm optimization algorithm is adopted to optimize the duty cycle of the poling period of the lithium niobate crystal. With this approach, the spectral purity can be improved from 0.820 to 0.998 under the third group‐velocity‐matched condition, and the wavelength‐tunable range from 3.0 to 4.0 µm for the degenerate case and 3.0 to 3.7 µm for the nondegenerate case. This work paves the way for developing quantum photonic technologies at the MIR wavelength band.
Mid-infrared quantum light sources hold broad application prospects in fields such as gas sensing and infrared thermal imaging. However, currently used mid-infrared quantum entangled light sources primarily rely on bulk periodically poled lithium niobate (PPLN) crystals, which limits brightness and integration. This paper proposes a theoretical scheme based on lithium niobate thin films, in which 1556.9 nm pumping is used to generate entangled photon pairs with a central wavelength of 3113.8 nm. By optimizing the waveguide structure and periodic polarization design, type-II phase matching and group velocity matching are achieved. This enables transverse electric (TE)-polarized pump input to be down converted to generate photon pairs with TE and transverse magnetic (TM) polarizations. Furthermore, by combining a domain arrangement algorithm used for the customized design of polarization direction in PPLN waveguides, precise phase matching is achieved, resulting in a quantum light source with a purity as high as 0.999 and a brightness of 6.18×106\times 10^6×106 cps/mW, which is three orders of magnitude higher than that of the bulk PPLN crystal source. This study provides a promising solution for realizing high-brightness, high-purity on-chip quantum light sources in the mid-infrared band.
The mid-infrared (MIR) band entangled photon source is vital for the next generation of quantum communication, quantum imaging, and quantum sensing. However, the current entangled states are mainly prepared in the visible or near-infrared bands. It is still lacking high-quality entangled photon sources in the MIR band. In this work, we optimize the poling sequence of lithium niobate to prepare two kinds of typical entangled states, the Hermit–Gaussian state and the comb-like entangled state at 3.2 µm. We have also calculated the photon pair rates and estimated the effect of fabrication resolution in the schemes. Our approach will provide entangled photon sources with excellent performance for the study of quantum information in the MIR band.
We theoretically investigate the preparation of mid-infrared (MIR) spectrally-uncorrelated biphotons from a spontaneous parametric down-conversion process using doped LN crystals, including MgO doped LN, ZnO doped LN, and In2O3 doped ZnLN with doping ratio from 0 to 7 mol%. The tilt angle of the phase-matching function and the corresponding poling period are calculated under type-II, type-I, and type-0 phase-matching conditions. We also calculate the thermal properties of the doped LN crystals and their performance in Hong-Ou-Mandel interference. It is found that the doping ratio has a substantial impact on the group-velocity-matching (GVM) wavelengths. Especially, the GVM2 wavelength of co-doped InZnLN crystal has a tunable range of 678.7 nm, which is much broader than the tunable range of less than 100 nm achieved by the conventional method of adjusting the temperature. It can be concluded that the doping ratio can be utilized as a degree of freedom to manipulate the biphoton state. The spectrally uncorrelated biphotons can be used to prepare pure single-photon source and entangled photon source, which may have promising applications for quantum-enhanced sensing, imaging, and communications at the MIR range.
Spontaneous parametric down-conversion (SPDC) spectroscopy using photon pairs is a promising avenue towards affordable mid-infrared (MIR) spectroscopy. Here, we experimentally investigate the feasibility of using periodically poled waveguides in lithium niobate for SPDC spectroscopy applications. We find the waveguides suitable to generate wavelength non-degenerate photon pairs with one photon in the MIR spectral range with high fluence. We use this to determine the cutoff wavelengths of the waveguide mode in the MIR by performing only measurements in the near-infrared spectral range.