‘Zero-point energy’ is a misnomer. It has come into use to describe the energy that exists in a complete vacuum, which without any atoms to create thermal energy must be at -273 degrees celsius.
The assumption that this is the lowest energy that anything can be, with the minimum level of energy of all atoms measured relative to this, emerges from Einstein’s denial of the existence of the aether. People are realising the aether does exist and contains energy. It is continually creating particles and anti-particles. Feynman said that there is enough energy in a mugful of the vacuum to boil all the oceans of the world. It seems that this energy can interact with electrons in a plasmoid, or perhaps creates electrons to make the plasma.
The ‘zero-point’, what we consider to be the minimum energy of matter, is better thought of as a ‘sea-level’ of energy. Confusing terms such as ‘negative energy’ then become understandable as something with less energy than an atom at ‘ground state’, but from which energy can still be extracted. Ashton Forbes, who has largely taught himself the science around this has done a useful review including video of scientists who have working on this in secret projects for more than a decade,
There are several companies that claim to have ‘above unity’ devices – devices which emit more energy than the energy required to start them running. What none have yet achieved is to make the excess energy power the device, turning it into a perpetual motion machine from which energy can be extracted. This may be a matter of only a couple of years away, if companies like ENG8 are to be believed. You can see a demonstration of their product.