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In the paper by Eric Davis referenced here:

https://www.mysterywire.com/documents/traversable-wormholes-stargates-and-negative-energy/

We find the following references to a squeezed vacuum on page 12, towards the bottom:

"Substantial theoretical and experimental work has shown that in many quantum systems the limits to measurement precision imposed by the quantum vacuum zero point fluctuations (ZPF) can be breached by decreasing the noise in one observable (measurable quantity) at the expense of increasing the noise in the conjugate observable; at the same time, the variations in the first observable, say the energy, becomes 'negative.'"

Eric Davis isn't exactly a mainstream physicist, and I am wondering if he is misinterpreting a more conventional process and what it means to say that vacuum energy density and flux is negative in the case of Quantum Field Theory. He also describes some experimental laser setups where supposed regions of squeezed vacuum can be established. Is this the same type of filtering that goes on in a Casimir cavity? Are we close to creating something truly fantastic like negative energy or mass? or is this just handwaving and fringe BS from a hype artist? I'd like some expert opinions.

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"Squeezed vacuum" is the name given to a state of the quantum harmonic oscillator which is like the ground state but has more uncertainty in one of the variables (such as position or momentum) and less in the other. It can be expressed as a superposition of energy eigenstates. When expressed that way only the eigenstates with even values of the vibrational quantum number contribute. It is a state whose mean energy is above the ground state energy. It is in many respects a perfectly ordinary state. The name is perhaps a little unfortunate because it suggests the state has something to do with the vacuum, which it doesn't particularly (any more than other excited states).

There is nothing physically impossible such as a mean energy below the ground state energy here.

Be careful of the term "exotic", by the way. It is often used when the writer could, and perhaps ought to, say "impossible in standard quantum theory" but they want to sneak something past our attention.

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In wikipédia, Squeezed coherent state, we can read : "Trivial examples, which are in fact not squeezed, are the ground state $ |0\rangle $ of the quantum harmonic oscillator and the family of coherent states $| \alpha \rangle$ ."

It is an application of the Bogoliubov transformations on the vacuum (Fock vacuum state).

For more technical details on squeezed states by A.Aspect, G.Grunberg and C.Fabre, starting on page 341.

The relation between the field phase and the photon number is applied in
the experiments of interaction of a field in a cavity by Serge Haroche.

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Casimir effect could be actually regarded as a "squezzed vacuum" effect in the sense that the number of allowed modes of modulation and frequency spectra are restricted by the distance of the two plates. You should really see the presentation and new published paper:

presentation

paper

Of a theoretical proposal and simulation of how this effect could be used to create a time wrap bubble which actually is an application of negative vacuum energy thus an Alcubierre warp metric.

While conducting analysis related to a DARPAfunded project to evaluate possible structure of the energy density present in a Casimir cavity as predicted by the dynamic vacuum model, a micro/nano-scale structure has been discovered that predicts negative energy density distribution that closely matches requirements for the Alcubierre metric. The simplest notional geometry being analyzed as part of the DARPA-funded work consists of a standard parallel plate Casimir cavity equipped with pillars arrayed along the cavity mid-plane with the purpose of detecting a transient electric field arising from vacuum polarization conjectured to occur along the midplane of the cavity. An analytic technique called worldline numerics was adapted to numerically assess vacuum response to the custom Casimir cavity, and these numerical analysis results were observed to be qualitatively quite similar to a two-dimensional representation of energy density requirements for the Alcubierre warp metric...

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