Using an Optical Parametric Amplifier as a Noiseless Attenuator

Heralded noiseless attenuators, in conjunction with noiseless amplifiers, have been shown to reduce the amount of decoherence a quantum state experiences when it travels through a lossy channel. Here, we introduce a novel noiseless attenuator that can be constructed by appropriate heralding on an optical parametric amplifier. This heralded parametric attenuator is somewhat surprising but it is a direct consequence of post-selecting on vacuum in the idler mode of the device.