  We define the statistical quadrature evolution (QE) method for multicarrier
continuous-variable quantum key distribution (CVQKD). A multicarrier CVQKD
protocol uses Gaussian subcarrier quantum continuous variables (CVs) for
information transmission. The QE scheme utilizes the theory of mathematical
statistics and statistical information processing. The QE model is based on the
Gaussian quadrature inference (GQI) framework to provide a minimal error
estimate of the CV state quadratures. The QE block evaluates a unique and
stable estimation of the non-observable continuous input from the measurement
results and through the statistical inference method yielded from the GQI
framework. The QE method minimizes the overall expected error by an estimator
function and provides a viable, easily implementable, and computationally
efficient way to maximize the extractable information from the observed data.
The QE framework can be established in an arbitrary CVQKD protocol and
measurement setting and is implementable by standard low-complexity functions,
which is particularly convenient for experimental CVQKD.
