  Real-world BB84 Quantum Key Distribution (QKD) systems utilize imperfect
devices that introduce vulnerabilities to their security, known as side-channel
attacks. Measurement-Device-Independent (MDI) QKD authorizes an untrusted third
party to make measurements and removes all side-channel attacks. The typical
implementations of MDI-QKD employ near symmetric channels which are difficult
to realize physically in many practical scenarios such as when asymmetric
channel losses are present, normally a consequence of the communication
environment. Maritime and satellite-based communications are two such instances
in which the channels are characterized by continuously changing losses in
different channels. In this work, we perform asymmetric MDI-QKD in a laboratory
environment with simulated turbulence using an Acousto-Optic Modulator (AOM) to
interrogate the performance of free-space quantum communication. Under
turbulent conditions, scattering and beam wandering cause intensity
fluctuations which decrease the detected signal-to-noise ratio. Using the
7-intensity optimization method proposed by Wang et al., coupled with
Prefixed-Threshold Real-time Selection (P-RTS), we demonstrate enhancement in
the secure key rate under turbulent conditions for finite-size decoy-state MDI
QKD. Furthermore, we show that P-RTS can yield considerably higher secure key
rates for a wide range of atmospheric channel parameters.
