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Journal of Physics Conference Series

Influence of light source and detector’s imperfections on the photon counting statistics

Aleksei Reutov, Сыч Денис Васильевич

Published Jul 1, 2021• 0 citations
Publisher

Abstract

Abstract Photon counting provides a valuable tool for measuring quantum properties of light. Unavoidable imperfections of photon detectors lead to discrepancies between the statistics of photons and statistics of photon counts. Here we consider dead-time corrections and influence of intensity fluctuations for simulated Poissonian statistics of photo counts for the pulsed or continuous wave coherent light sources. We analyse dependence between the statistical moments of corrected distribution and the mean photon number, dead-time, and level of intensity fluctuations.

DOI
10.1088/1742-6596/1984/1/012009

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Abstract Photon counting provides a valuable tool for measuring quantum properties of light. Unavoidable imperfections of photon detectors lead to discrepancies between the statistics of photons and statistics of photon counts. Here we consider dead-time corrections and influence of intensity fluctuations for simulated Poissonian statistics of photo counts for the pulsed or continuous wave coherent light sources. We analyse dependence between the statistical moments of corrected distribution and the mean photon number, dead-time, and level of intensity fluctuations.
Abstract Measurement of photon statistics is an important tool for the verification of quantum properties of light. Due to the various imperfections of real single photon detectors, the observed statistics of photon counts deviates from the underlying statistics of photons. Here we analyze statistical properties of coherent states, and investigate a connection between Poissonian distribution of photons and sub-Poissonian distribution of photon counts due to the detector dead-time corrections. We derive a functional dependence between the mean number of photons and the mean number of photon counts, as well as connection between higher-order statistical moments, for the pulsed or continuous wave coherent light sources, and confirm the results by numerical simulations.
Photonic quantum technologies require single photon sources and detectors operating at high efficiency, but at high rates detector imperfections can lead to inaccurate measurements. We show that the combination of the detector deadtime and the source statistics together determine the saturation level of a single photon detector, with anti-bunched sources leading to a greater detection rate than coherent or thermal light of the same intensity. At high photon rates this behavior distorts second-, third- and fourth- order correlation measurements, in agreement with our numerical simulations. Finally, we discuss the implications for entangled light detection and photonic logic.
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.
If a beam of light is coherent, then the photons constituting the beam arrive at random moments in time. Consequently, the photon counting statistics in a given time interval below the coherence time, should in theory follow a Poissonian distribution. When the measurement interval exceeds the coherence time, the distribution should broaden and become a super-Poissonian distribution. The aim of this study is to experimentally demonstrate the Poissonian nature of light, as well as quantifying the transition to a super-Poissonian distribution. In the experiment, a low-intensity laser beam was measured with single-photon detectors, able to capture individual photons. The arrival time of the photons was detected with an oscilloscope, and the data further analysed with our own Python code. The probability distribution of the arrival time of photons was constructed and fitted with a Poissonian distribution for different time intervals. The results showed a clear Poissonian distribution for all intervals from 0.2 μs up to 2000 μs. We did however, observe tendencies of randomness for the longest measured intervals. A Poissonian distribution is defined by the variance being equal to the mean, whilst for a super-Poissonian distribution the variance is higher. The biggest measured ratio between the variance and the mean in our experiment was 1.06 for interval time 2000 μs, which is too small to infer super-Poissonian. Due to limited data memory, our dataset was restricted in length and resolution. Therefore, longer intervals could not be studied without statistical uncertainty. To cross-check the result we also calculated the probability distribution for the arrival time itself. The result perfectly fitted an exponential distribution which was in accordance with the theory of coherent light. Hence, within the given measurement accuracy and statistical uncertainty, it is safe to conclude that the laser beam is coherent for all tested time intervals. However, this does not allow us to conclude that it is a single-mode laser.
The widely used experimental technique of continuous-wave detection assumes counting pulses of photocurrent from a click-type detector inside a given measurement time window. With such a procedure we miss out the photons detected after each photocurrent pulse during the detector dead time. Additionally, each pulse may initialize a so-called afterpulse, which is not associated with the real photons. We derive the corresponding quantum photocounting formula and experimentally verify its validity. Statistics of photocurrent pulses appears to be nonlinear with respect to the quantum state, which is explained by the memory effect of the previous measurement time windows. Expressions---in general, nonlinear---connecting statistics of photons and pulses are derived for different measurement scenarios. We also consider an application of the obtained results to quantum state reconstruction with unbalanced homodyne detection.
Single-photon detectors are “blind” after the detection of a photon, and thereafter display a characteristic recovery in efficiency, during which the number of undetected photons depends on the statistics of the incident light. We show how the efficiency recovery, photon statistics, and intensity have an interdependent relationship which suppresses a detector’s ability to count photons and measure correlations. We also demonstrate this effect with an experiment using n such detectors to determine the n th -order correlation function with pseudothermal light. Published by the American Physical Society 2024