There are claims that LENR extracts energy from the vacuum. The question naturally arises about how can such an improbable thing can possibly happen.
A experiment done using a optical cavity shows how the vacuum can tap into the vacuum fluctuations that occur in empty space to produce real effects. http://www.pnas.org/content/110/11/4234.full.pdf Dynamical Casimir effect in a Josephson metamaterial This experiment shows how an optical cavity can be tuned electrically using the KERR effect in such a way to convert virtual photons into real photons through the adjustment of the index of refraction of the vacuum in the cavity to produce a resonance based casimir effect. The KERR effect is a mechanism to adjust the speed of light in the vacuum so that the cavity can be modified into a resonance condition in such a way as to use the casimir effect to extract real photons from the vacuum. This KERR effect adjustment mechanism might be operable in LENR as well as the EMDRIVE. Quote The zero-point energy stored in the modes of an electromagnetic cavity has experimentally detectable effects, giving rise to an attractive interaction between the opposite walls, the static Casimir effect. A dynamical version of this effect was predicted to occur when the vacuum energy is changed either by moving the walls of the cavity or by changing the index of refraction, resulting in the conversion of vacuum fluctuations into real photons. Here, we demonstrate the dynamical Casimir effect using a Josephson metamaterial embedded in a microwave cavity at 5.4 GHz. We modulate the effective length of the cavity by flux-biasing the metamaterial based on superconducting quantum interference devices (SQUIDs), which results in variation of a few percentage points in the speed of light. We extract the full 4 × 4 covariance matrix of the emitted microwave radiation, demonstrating that photons at frequencies symmetrical with respect to half of the modulation frequency are generated in pairs. At large detunings of the cavity from half of the modulation frequency, we find power spectra that clearly show the theoretically predicted hallmark of the Casimir effect: a bimodal, “sparrow-tail” structure. The observed substantial photon flux cannot be assigned to parametric amplification of thermal fluctuations; its creation is a direct consequence of the noncommutativity structure of quantum field theory.