  Photon subtraction can enhance the performance of continuous-variable quantum
key distribution (CV QKD). However, the enhancement effect will be reduced by
the imperfections of practical devices, especially the limited efficiency of a
single-photon detector. In this paper, we propose a non-Gaussian postselection
method to emulate the photon substraction used in coherent-state CV QKD
protocols. The virtual photon subtraction not only can avoid the complexity and
imperfections of a practical photon-subtraction operation, which extends the
secure transmission distance as the ideal case does, but also can be adjusted
flexibly according to the channel parameters to optimize the performance.
Furthermore, our preliminary tests on the information reconciliation suggest
that in the low signal-to-noise ratio regime, the performance of reconciliating
the postselected non-Gaussian data is better than that of the Gaussian data,
which implies the feasibility of implementing this method practically.
