Phys.org  September 17, 2020 Phase-sensitive optical amplifiers (PSAs) with their uniquely low noise figure of 0 dB promise to provide the best possible sensitivity for Gb/s-rate long-haul free-space links. An international team of researchers (Sweden, USA – MIT, UC San Diego, industry, Japan) demonstrate a novel approach using a PSA-based receiver in a free-space transmission experiment with an unprecedented bit-error-free, black-box sensitivity of 1 photon-per-information-bit (PPB) at an information rate of 10.5 Gb/s. The system adopts a simple modulation format (quadrature-phase-shift keying, QPSK), standard digital signal processing for signal recovery and forward-error correction and is straightforwardly scalable to higher data rates…read more. […]