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The wigner function of squeezed state has no negative values. And as far as I know a nagative value is an indecator of quantum effects. So does that mean a squeezed state is a classical light?

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    $\begingroup$ Positivity of WF is not a necessary and stufficient condition for classicality; the counterexample is exactly squeezed states. $\endgroup$ Feb 25 '19 at 2:50
  • $\begingroup$ @ZeroTheHero then what is it that is quantum about squeezed states? $\endgroup$
    – Jagerber48
    Feb 25 '19 at 5:00
  • $\begingroup$ @jgerber one of the variances will be below the standard quantum limit. $\endgroup$ Feb 25 '19 at 14:17
  • $\begingroup$ @ZeroTheHero classically there is no limit to how small the Quadra tire variances can become so there must be a longer story to explain what non classical phenomena arise with squeezed states $\endgroup$
    – Jagerber48
    Feb 25 '19 at 14:59
  • $\begingroup$ @jgerber I don't follow. There is a well-defined standard quantum limit, obtained from coherent states which are themselves "classical". If you beat this SQL with a state, this state is quantum. Of course you can only do this because the state contains quantum correlations. $\endgroup$ Feb 25 '19 at 15:01

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