An apparatus and method are disclosed for maximizing interference contrast in an interferometric quantum cryptography system to detect eavesdropping by utilizing a tunable emitter station in communications with a receiver station via a quantum communications channel and a “public” communications channel. The tunable emitter station tracks and compensates for interferometer drifts by adjusting the interference contrast of the QC system to minimize or eliminate inherent perturbations induced into key bit transmissions. Tuning of the photo emitter's output wavelength is accomplishable using temperature and/or drive current adjustment of the emitter's tunable optical subsystem.