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Pure single photon generation from nonlinear processes

机译：非线性过程产生的纯单光子

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摘要

Summary form only given. Parametric downconversion (PDC) allows the generation of highly coherent, spectrally pure single photons for quantum photonics. In a typical heralded PDC source, the signal photon emerges in a spectrally mixed state due to strong (anti)correlation in the joint spectrum of PDC photon pairs.One method for reducing spectral correlations is spectral filtering, but this compromises the heralding efficiency and the brightness of the source. A more sophisticated method for increasing the heralded photon purity is group-velocity matching, which works by erasing part of the timing information between the pump and PDC photons. What group-velocity matching cannot address, however, are the remaining correlations in the joint spectrum that come from the sinc-shaped phase-matching function (PMF) typical to standard PDC crystals. Further source engineering is therefore required to remove these correlations. Several studies have introduced domain-engineering techniques for shaping the phase matching function (PMF) in periodically poled crystals to improve single photon purities [1-4]. We present a new technique for tailoring crystal nonlinearities which combines the advantages of a deterministic method for domain engineering [4] and an annealing method developed for classical applications in higher-harmonic generation [5]. In our method, we first choose each domain orientation such that the generated field amplitude along the crystal matches the target field amplitude obtained by integrating the desired nonlinearity profile. Using a one-block structure instead of a two-blocks structure (as in [4]) results in a higher flexibility of the algorithm in tracking the target function and yields to more accurate results. We then use an annealing algorithm to slightly vary the width of each domain, further improving the effective PMF. Our technique outperforms its predecessors, particularly for short crystals, leading to high single photon purities, as shown in Fig.1. We experimentally characterise our method through a high-precision measurement of multiphoton interference between two heralded photons generated by two independent sources.We also notice that by considering a complex target field amplitude function it is possible to generalise the algorithm in [5] to any constant domain width (not necessarily equal to the coherence length), leading to a better approximation of the desired phase matching function, especially in the very short crystal regime. Moreover, tracking both the real and imaginary components of the target function allows us to approximate more exotic cases such as chirped nonlinearity profiles. Since scalable quantum photonics will require integrated architectures in which nonlinear processes are typically employed for single-photon generation, it will be interesting to explore new techniques similar to in-fibre Bragg grating structures which might yield quasi-periodic four-wave mixing and apply our algorithm to these new platforms.
机译：仅提供摘要表格。参数下变频（PDC）允许为量子光子产生高度相干的，光谱纯净的单光子。在典型的预示PDC源中，由于PDC光子对的联合光谱中的强（反）相关性，信号光子以光谱混合状态出现。减少光谱相关性的一种方法是光谱滤波，但这会降低预示效率和光源的亮度。组速度匹配是提高先驱光子纯度的一种更复杂的方法，它可以通过擦除泵浦和PDC光子之间的部分定时信息来工作。但是，群速度匹配无法解决的是联合频谱中的其余相关性，这些相关性来自于标准PDC晶体典型的Sinc形相位匹配函数（PMF）。因此，需要进一步的源代码工程来删除这些相关性。多项研究已经引入了域工程技术，以在周期性极化的晶体中成形相位匹配函数（PMF），以提高单光子纯度[1-4]。我们提出了一种用于定制晶体非线性的新技术，该技术结合了领域工程确定性方法的优势[4]和为高次谐波产生的经典应用开发的退火方法[5]。在我们的方法中，我们首先选择每个畴的方向，以使沿晶体产生的场振幅与通过积分所需的非线性分布而获得的目标场振幅相匹配。使用一个块的结构而不是两个块的结构（如[4]所示）会导致算法在跟踪目标函数时具有更高的灵活性，并获得更准确的结果。然后，我们使用退火算法稍微改变每个域的宽度，从而进一步提高有效PMF。如图1所示，我们的技术优于以前的技术，特别是对于短晶体，从而导致高单光子纯度。我们通过高精度测量由两个独立源产生的两个先驱光子之间的多光子干涉来实验性地描述我们的方法。我们还注意到，通过考虑复杂的目标场振幅函数，可以将[5]中的算法推广到任何常数区域宽度（不一定等于相干长度），导致更好地逼近所需的相位匹配函数，尤其是在非常短的晶体状态下。此外，跟踪目标函数的实部和虚部都使我们能够近似更奇特的情况，例如chi非线性轮廓。由于可扩展的量子光子将需要集成的体系结构，在该体系结构中通常会使用非线性过程来生成单光子，因此探索类似于光纤布拉格光栅结构的新技术（可能会产生准周期四波混频）并应用我们的技术将非常有趣。这些新平台的算法。

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  • 来源
  • 会议地点 Munich(DE)
  • 作者

    Francesco Graffitti; Dmytro Kundys; Derryck T. Reid; Agata Brańczyk; Alessandro Fedrizzi;

  • 作者单位

    Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK;

    Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK;

    Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK;

    Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK;

    Scottish Universities Physics Alliance (SUPA), Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK;

  • 会议组织
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    Photonics; Crystals; Frequency conversion; Correlation; Physics; Annealing; Target tracking;

    机译：光子学;晶体;频率转换;相关;物理;退火;目标跟踪;;

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