  A promising result from optical quantum metrology is the ability to achieve
sub-shot-noise performance in transmission or absorption measurements. This is
due to the significantly lower uncertainty in light intensity of quantum beams
with respect to their classical counterparts. In this work, we simulate the
outcome of an experiment that uses a multiplexed single-photon source based on
pair generation by continuous spontaneous parametric down conversion (SPDC)
followed by a time multiplexing set-up with a binary temporal division
strategy, considering several types of experimental losses. With such source,
the sub-Poissonian statistics of the output signal is the key for achieving
sub-shot-noise performance. We compare the numerical results with two
paradigmatic limits: the shot-noise limit (achieved using coherent sources) and
the quantum limit (obtained with an ideal photon-number Fock state as the input
source). We also investigate conditions in which threshold detectors can be
used, and the effect of input light fluctuations on the measurement error.
Results show that sub-shot-noise performance can be achieved, even without
using number-resolving detectors, with improvement factors that range from 1.5
to 2. This technique would allow measurements of optical absorption of a sample
with reasonable uncertainty using ultra-low light intensity and minimum
disruption of biological or other fragile specimens.
