Estimation of mean photon number based on single photon detection of weak coherent pulses

Abstract

The demand for single photon sources in quantum key distribution (QKD) systems has necessitated the 
use of weak coherent pulses (WCPs) characterized by a Poissonian distribution. Ensuring security against 
eavesdropping attacks requires keeping the mean photon number (µ) small and known to legitimate partners. However, 
accurately determining µ poses challenges due to discrepancies between theoretical calculations and practical 
implementation. This paper introduces two experiments. The first experiment involves theoretical calculations of µ 
using several filters to generate the WCPs. The second experiment utilizes a variable attenuator to generate the WCPs, 
and the value of µ was estimated from the photons detected by the BB84 detection setup. The second experiment 
represents an accurate method for estimating the value of µ because of using single photon detectors with high timing 
resolution and low dark counts, in addition to using a Time-to-digital convertor with a bin size of 81 ps.