  In this work we propose the technique for phase-coded weak coherent states
protocols utilizing two signal states and one decoy state which is found as
linear combination of signal states (Schr\"odinger Cat states); the latter
allows to overcome the USD attack. For instance, Schr\"odinger Cat states can
be considered as even coherent states. Moreover we consider decoy states
implementation based on squeezed vacuum states which might not disables USD
completely yet produces discrimination probabilities low enough to distribute
keys in channel with particular losses. Thus we can detect Eve simply by
monitoring the detection rate of decoy states. It should be noted that this
approach can be scaled to more complex schemes.
