State-dependent linear-optical qubit amplifier.

We propose a linear-optical setup for heralded qubit amplification with tunable output qubit fidelity. We study its success probability as a function of output qubit fidelity, showing that at the expense of lower fidelity, the setup can considerably increase probability of successful operation. These results are subsequently applied in a proposal for state-dependent qubit amplification. Similar to state-dependent quantum cloning, the a priori information about the input state allows us to optimize the qubit amplification procedure to obtain a better fidelity versus success probability trade-off [ABSTRACT FROM AUTHOR]