Noiseless Signal Amplification using Positive Electro-Optic Feedforward

We propose an electro-optic feedforward scheme which can in principle produce perfect noiseless signal amplification (signal transfer coefficient of $T_{\mathrm{s}}=1\mathrm{}$). We demonstrate the scheme experimentally and report, for a signal gain of 13.4 dB, a signal transfer coefficient of $T_{\mathrm{s}}=0.88\mathrm{}$ which is limited mainly by detector efficiencies (92%). The result clearly exceeds the standard quantum limit, $T_{\mathrm{s}}=0.5\mathrm{}$, set by the high gain limit of a phase insensitive linear amplifier. We use the scheme to amplify a small signal carried by 35% amplitude squeezed light and demonstrate that, unlike the fragile squeezed input, the signal amplified output is robust to propagation losses.