Phase-sensitive amplification via coherent population oscillations in   metastable helium at room temperature
  We report our experimental results on phase-sensitive amplification (PSA) in non-degenerate signal-idler configuration using ultra-narrow coherent population oscillations in metastable helium at room temperature. We achieved a high PSA gain of nearly 7 with a bandwidth of 200 kHz, by using the system at resonance in a single-pass scheme. Further, the measured minimum gain is close to the ideal value, showing that we have a pure PSA. This is also confirmed from our phase-to-phase transfer curves measurements, illustrating that we have a nearly perfect squeezer, which is interesting for a variety of applications. 
J. Lugani, C. Banerjee, M-A. Maynard, P. Neveu, W. Xie, R. Ghosh, F.   Bretenaker, F. Goldfarb
quant-ph