According to Heisenberg the world unobserved exists in a state of POTENTIA, a bundle of mere possibilities, tendencies to exist, a state of existence, in Heisenberg's words, halfway between an idea and a thing.
But when the world is observed, in what physicists call "an irreversible measurement act", one of these unreal quantum potentias turns real and enters the world as a ACTUALITY. All other potentias completely vanish as though they had never been.
POTENTIA before observation; ACTUALITY after observation: that's quantum reality according to Heisenberg.
Recently some researchers have been investigating under what conditions this situation can be reversed. What would you have to do in the world to turn ACTUALITY back into POTENTIA?
Early work along these lines goes by the name "the quantum eraser effect". Physicist and author Casey Blood sent me a nice web page on quantum erasure.
In a paper published today in the physics arXiv, Andrew Jordan at the University of Rochester and Alexander Korotkov from UC Riverside have proposed to "uncollapse the wavefunction by undoing quantum measurements" using techniques more drastic than the quantum eraser. After a century of effort the quantum measurement problem still remains one of the great unsolved questions in physics. Drs. J and K propose to shed new light on the problem of measurement by investigating the inverse process of "unmeasurement"--uncovering the conditions under which solid ACTUALITY can be turned back into dreamy POTENTIA.
Obviously if this measurement is in your head some kind of amnesia must happen. You're going to have to forget the value of whatever variable you happened to measure as you very carefully return the system to its original unmeasured state.
The authors discuss the unmeasurement process in theory but also apply their thinking to a variety of actual quantum systems, including quantum dots, superconducting phase qubits, electron spins and polarization states. It appears that for these small systems unmeasurement is a realizable option.
The difficulties of achieving unmeasurement increase with the size of the system so it's highly unlikely that we could weaponize this process to create a Unreality Ray that infects everything in its path with a kind of atomic Alzheimer's thus returning formerly solid matter to the Taoist's original Uncarved Block. Unreality Rays are surely the stuff of science fiction; the future of J & K's "uncollapse process" may lie instead in a sort of friendly competition between physics labs to see just how big a piece of actuality one can really unmeasure.
Let the games begin.
Gentlemen, deploy your tools of unmeasurement.