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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

QPMoptics: a novel tool to simulate and optimise photon pair creation

Fabian Laudenbach, Hannes Hübel, Michael Hentschel, Andreas Poppe

Published Apr 27, 2016• 3 citations
Publisher

Abstract

We present a new scientific software which is able to simulate any experimental setup based on photon pair creation with spontaneous parametric down-conversion in periodically poled crystals. Moreover, our software is able to optimise experimental parameters for the sake of high down-conversion efficiency and quantum performance. Given the optional input of any relevant individual experimental setup, the large number of output parameters and plots and the user-friendly intuitive graphical user interface, we believe that our software can be a helpful tool to any experimentalist who uses the quasi-phase-matching technique to generate collinearly propagating photon pairs.

DOI
10.1117/12.2230141

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We present a new scientific software which is able to simulate any experimental setup based on photon pair creation with spontaneous parametric down-conversion in periodically poled crystals. Moreover, our software is able to optimise experimental parameters for the sake of high down-conversion efficiency and quantum performance. Given the optional input of any relevant individual experimental setup, the large number of output parameters and plots and the user-friendly intuitive graphical user interface, we believe that our software can be a helpful tool to any experimentalist who uses the quasi-phase-matching technique to generate collinearly propagating photon pairs.
We present a scheme for engineering the joint spectrum of photon pairs created via spontaneous parametric down-conversion. Our method relies on customizing the poling configuration of a quasi-phase-matched crystal. We use simulated annealing to find an optimized poling configuration which allows almost arbitrary shaping of the crystal's phase-matching function. This has direct application in the creation of pure single photons---currently one of the most important goals of single-photon quantum optics. We describe the general algorithm and provide code, written in C++, that outputs an optimized poling configuration given specific experimental parameters.
The process of spontaneous parametric down-conversion (SPDC) in nonlinear crystals makes it fairly easy to generate entangled photon states. It has been known for some time that the conversion efficiency can be improved by employing quasi-phase-matching in periodically poled crystals. Using two single-photon detectors, we have analyzed the photon pairs generated by SPDC in a periodically poled lithium niobate crystal pumped by a femtosecond laser. Several parameters could be varied in our setup, allowing us to obtain data in close agreement with both thermal and Poissonian photon-pair distributions.
High-brightness correlated photon pairs at longer wavelengths are of key interest for mid-infrared quantum imaging, spectroscopy, and sensing applications. Here, we report numerically investigated optimum conditions for the generation of correlated photon pairs via the spontaneous parametric down-conversion (SPDC) process at longer wavelengths, exploiting bulk quasi-phase-matched (QPM) nonlinear crystals. Using numerical simulation within a unified numerical analysis framework, the performance of various crystals in terms of emission angles in non-collinear interaction, the spatial profile of correlated photon pairs, and the absolute gain has been evaluated. Among the crystals studied, orientation-patterned gallium arsenide has been found to demonstrate significant potential for photon pair generation in mid-infrared (IR), with high absolute gain. In line with the analysis performed, we have further developed a web-deployable numerical analysis platform for efficient SPDC in QPM nonlinear crystals under optimal conditions across near-IR to mid-IR. The findings of this work contribute to the advancement of quantum technologies by offering insights into the design and optimization of high-brightness single-photon sources from near-IR to mid-IR, while providing an interactive numerical analysis platform for the systematic investigation of phase-matching and gain characteristics.
We present a theoretical and experimental study of the angular and temperature dependence of the photon pairs produced by spontaneous parametric down-conversion in a periodically poled KTP crystal. In the experiment, two detectors are placed at different angles in the emitted light, and the detected photon pair rate is measured as a function of one angle or of crystal temperature. In the theoretical work, exact results for the pair rates are obtained through importance-sampled numerical integration of the fourth-order coherence function over regions representing the experimental integration parameters. Conditions studied range from well-resolved results in which detector angular and filter bandwidth integration effects are negligible, to other cases in which such effects are large and pair rates exceed ${10}^{5}\phantom{\rule{4pt}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. Throughout these cases, good agreement is often seen between experimental and theoretical results, while some differences that are noted provide insight into the actual crystal quasi-phase-matching function.
For advanced quantum information technology, sources of photon pairs in quantum mechanically factorable states are of great importance for realizing high-fidelity photon-photon quantum gate operations. Here we experimentally demonstrate a technique to produce spectrally factorable photon pairs utilizing multi-order quasi-phase-matching (QPM) conditions in spontaneous parametric downconversion (SPDC). In our scheme, a spatial nonlinearity profile of a nonlinear optical crystal is shaped with current standard poling techniques, and the associated phase-matching function can be approximated to a Gaussian form. By the measurement of a phase-matching function and the second-order autocorrelation function, we demonstrate that telecom-band photon pairs produced by our custom-poled crystal are highly factorable with > 95% single-photon purity.
Pair creation by spontaneous parametric down-conversion (SPDC) has become a reliable source for single-photon states, used in many kinds of quantum information experiments and applications. In order to be spectrally pure, the two photons within a generated pair should be as frequency-uncorrelated as possible. For this purpose most experiments use narrow bandpass filters, having to put up with a drastic decrease in count rates. This article elaborates (theoretically and by numerical evaluation) the alternative method to engineer a setup such that the SPDC-generated quantum states are intrinsically pure. Using pulsed pump lasers and periodically poled crystals this approach makes bandpass filtering obsolete and allows for significantly higher output intensities and therefore count rates in the detectors. After numerically scanning all common wavelength regimes, polarisation configurations and three different non-linear crystals, we present a broad variety of setups which allow for an implementation of this method.