Non-deterministic noiseless amplification via non-symplectic phase space   transformations
  We analyse the action of an ideal noiseless linear amplifier operator, $g^\hat{n}$, using the Wigner function phase space representation. In this setting we are able to clarify the gain $g$ for which a physical output is produced when this operator is acted upon inputs other than coherent states. We derive compact closed form expressions for the action of $N$ local amplifiers, with potentially different gains, on arbitrary $N$-mode Gaussian states and provide several examples of the utility of this formalism for determining important quantities including amplification and the strength and purity of the distilled entanglement, and for optimising the use of the amplification in quantum information protocols. 
Nathan Walk, Austin P. Lund, Timothy C. Ralph
quant-ph