Quantum physics is on a lot of peoples' minds these days.
It is of course, one of the two theories that have resisted integration into a single scaffolding of natural laws - the other being gravity. But even considered on its own, quantum physics seems to be a subject whose foundations are mired in controversy. Every few days there appears a paper declaiming that there is no problem with quantum mechanics, and another saying that there is a problem and it can be fixed as prescribed, and yet another stating that there is a problem and it is far from being solvable. Every few months, there is a new book on quantum physics to placate the hunger that seems as perennial as the one fed by titles on optimal management practices, financial success and weight loss.
But quantum now also figures prominently in the news as an identified source of next-generation technological innovation. Governments have been pouring tens of billions of dollars (USD) into quantum research and enterpreneurship over the last few years. There is talk and quantification of 'quantum supremacy', the point at which quantum physics becomes clearly more capable than classical methods.
So I thought it may not be a bad time to reconsider some common impressions about quantum mechanics and compare them to - sometimes subtle rejoinders from - state of the art knowledge. Here's a list of ten:
i) The quantum wavefunction is not a physical object as only its absolute magnitude squared - in other words the probability - can be measured. But see this paper about experimental measurement of the quantum wavefunction, already more than a decade old.
ii) It is not possible to beat the Heisenberg Uncertainty Principle. But see this paper.
iii) Quantum mechanics is non-local. Therefore it can be used to transfer information faster than the speed of light. But see the no-communication theorem.
v) Quantum jumps are completely random. But see this amazing experiment performed at Yale in the group of Michel Devoret, following the theoretical proposal of Howard Carmichael. It shows that quantum jumps are unpredictable on long time scales, but are deterministically predictable on short time scales. They can even be reversed!
vi) Quantum teleportation can be used to transport material objects. No, just the quantum state of the object.
vii) Quantum mechanics implies that all physical variables are allowed to take on discrete values. No, depending on the context, physical variables can be continuous in quantum theory, such as position for a free - quantum - particle.
viii) Quantum physics says everything is random. No, the evolution of any quantum system - before measurement - is given by Schrodinger's equation, which is deterministic.
ix) The existence of the multiverse has been proven. No, but the concept has received some Oscars.
x) It is necessary to fully understand quantum mechanics before using it. No, a large number of physicists use it while disagreeing about the fundamental interpretation, if any, of the theory. It is currently not clear what a full understanding of quantum physics entails.
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