Extra phase noise from thermal fluctuations in non-linear optical crystals

Recent experiments with Optical Parametric Oscillators have shown [1–3] that an unpredicted extra noise on the phase of the fields reduces the level of squeezing or quantum correlations. In some cases, it can hinder the attempts to observe entanglement in those systems [4]. It is probably the main reason why signal and idler entanglement above threshold remained unobserved by almost 20 years after its prediction [5].