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## Summary:

- Propagation of phonon in BEC, several contributions

Hi, I have some problems with visualization (I'm trying to understand Jeff Steinhauer's experiment, but my questions are general).

Why the quantum vacuum fluctuations are

And if vacuum fluctuations generate excitations (i.e phonon) what is the link with the propagation of wave? Does this excitation produce waves? There are propagating waves plus excitation due to vacuum fluctuations?

And more specifically, he used the correlation between annihilation operators for demonstrated the Hawking radiation but why not the creation operators?

Thanks

Why the quantum vacuum fluctuations are

*guaranteed*by the underlying pointlike atoms composing a BEC?And if vacuum fluctuations generate excitations (i.e phonon) what is the link with the propagation of wave? Does this excitation produce waves? There are propagating waves plus excitation due to vacuum fluctuations?

And more specifically, he used the correlation between annihilation operators for demonstrated the Hawking radiation but why not the creation operators?

Thanks