We present a simple protocol to purify a coherent-state superposition thathas undergone a linear lossy channel. The scheme constitutes only a single beamsplitter and a homodyne detector, and thus is experimentally feasible. Inpractice, a superposition of coherent states is transformed into a classicalmixture of coherent states by linear loss, which is usually the dominantdecoherence mechanism in optical systems. We also address the possibility ofproducing a larger amplitude superposition state from decohered states, andshow that in most cases the decoherence of the states are amplified along withthe amplitude.
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