Toward perfect homodyne detection of twin vacuum beams

We demonstrate the use of an optical phase-sensitive amplifier to recover the quantum correlations in twin light beams after degradation due to optical loss and detector efficiency. We use four-wave mixing in hot $^{85}$Rb vapor cell to generate correlated twin beams in a two-mode squeezed vacuum state. We then use a second four-wave mixing cell as our optical phase-sensitive amplifier to amplify one half of the two-mode state, which can compensate for downstream optical loss and restore the nonclassical correlations of the state.