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Journal of the Optical Society of America B

Photon-count fluctuations of spontaneous parametric down conversion exhibit long-range correlations

Lian Seng Tey, Sithi Vinayakam Muniandy, Wu Yi Chong

Published Aug 5, 2024• 3 citations
Publisher

Abstract

We investigate the fluctuation dynamics of photons generated by spontaneous parametric down conversion (SPDC) using detrended fluctuation analysis (DFA). SPDC photon pairs were generated via a periodically poled potassium titanyl phosphate waveguide, pumped by a 405 nm continuous-wave laser. The scaling exponents obtained from DFA reveal that SPDC photons exhibit long-range correlations at high pump power regimes. The average scaling exponent of DFA increases from 0.67 to 0.97 as the laser diode drive current increases, indicating the existence of long-range correlations. Our analysis concluded that the scaling exponent of aggregated time series is correlated to the number of SPDC photon pairs.

DOI
10.1364/josab.527547

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We investigate the fluctuation dynamics of photons generated by spontaneous parametric down conversion (SPDC) using detrended fluctuation analysis (DFA). SPDC photon pairs were generated via a periodically poled potassium titanyl phosphate waveguide, pumped by a 405 nm continuous-wave laser. The scaling exponents obtained from DFA reveal that SPDC photons exhibit long-range correlations at high pump power regimes. The average scaling exponent of DFA increases from 0.67 to 0.97 as the laser diode drive current increases, indicating the existence of long-range correlations. Our analysis concluded that the scaling exponent of aggregated time series is correlated to the number of SPDC photon pairs.
Understanding photon-count dynamics is crucial for applications such as quantum random number generators and quantum key distributions, where random and memoryless photon-count arrival processes are essential for performance and security. We investigated the fluctuation dynamics of aggregated photon-count time series for two distinct light sources: a 780-nm laser diode and a spontaneous parametric down-conversion source, using detrended fluctuation analysis (DFA) and the index of dispersion for intervals (IDI). Despite the degradation of photon statistics to Poissonian due to optical losses and detector inefficiencies, our analysis reveals significant long-range dependence at large timescales. The DFA scaling exponents α[over ¯]>0.75 and IDI values c_{k}^{2}>1 at high mean photon count and large aggregation timescales indicate photon-count fluctuations deviated from Poisson model. Our findings underscore the necessity of models beyond Poisson statistics to accurately describe the photon-count dynamics over extended timescales.
We present a simple but highly efficient source of polarization-entangled photons based on spontaneous parametric down-conversion (SPDC) in bulk periodically poled potassium titanyl phosphate crystals (PPKTP) pumped by a 405 nm laser diode. Utilizing one of the highest available nonlinear coefficients in a non-degenerate, collinear type-0 phase-matching configuration, we generate polarization entanglement via the crossed-crystal scheme and detect 0.64 million photon pair events/s/mW, while maintaining an overlap fidelity with the ideal Bell state of 0.98 at a pump power of 0.025 mW.
We present a simple but highly efficient source of polarization-entangled photons based on spontaneous parametric down-conversion (SPDC) in bulk periodically poled potassium titanyl phosphate crystals (PPKTP) pumped by a 405 nm laser diode. Utilizing one of the highest available nonlinear coefficients in a non-degenerate, collinear type-0 phase-matching configuration, we generate polarization entanglement via the crossed-crystal scheme and detect 0.64 million photon pair events/s/mW, while maintaining an overlap fidelity with the ideal Bell state of 0.98 at a pump power of 0.025 mW.
The properties of the backward-wave spontaneous parametric down-conversion (SPDC) in a periodically poled potassium titanyl phosphate (KTP) waveguide are studied in the context of creating narrowband heralded sources of single-photon states. The effective index of refraction and spatial profile of different waveguide modes, efficiency of different SPDC processes and purity of heralded photons are calculated numerically for a given waveguide. Compared to the usual co-propagating SPDC, spectral narrowing of the backward-wave SPDC was observed as should be expected. Generation biphoton states in backward-wave regime is experimentally observed in two-photon detection scheme.
The properties of the backward-wave spontaneous parametric down-conversion (SPDC) in a periodically poled potassium titanyl phosphate (KTP) waveguide are studied in the context of creating narrowband heralded sources of single-photon states. The effective index of refraction and spatial profile of different waveguide modes, efficiency of different SPDC processes and purity of heralded photons are calculated numerically for a given waveguide. Compared to the usual co-propagating SPDC, spectral narrowing of the backward- wave SPDC was observed as should be expected.
Over the past decade, counter-propagating spontaneous parametric down-conversion (CPSPDC) has attracted interest due to its ability to generate narrowband and spectrally pure photon pairs without the need for strong spectral filtering. While prior work has established the spectral characteristics of CPSPDC, its performance as a heralded single-photon source (HSPS) remains limited. Here, we present a detailed HSPS characterization of a first-order quasi-phase-matched CPSPDC source based on a sub-μm periodically poled potassium titanyl phosphate crystal. We measure an internal pair-generation rate of 1.3×10 3 pairs/s/mW under CW pumping, in addition to a high coincidence-to-accidental ratio exceeding 1.4×10 5 , and furthermore obtain the lowest heralded second-order correlation value of (8.57±4.95)×10 -6 ever reported. We also show a Hong–Ou–Mandel interference experiment that yields a raw visibility of 70±1%, confirming photon indistinguishability. These results demonstrate CPSPDC as a strong candidate for generating high-quality single photons for quantum information processing and long-distance quantum communication applications.