I have come across this paper which very explicitly claims that decoherence does not solve the measurement problem and never claimed to. Which is it? Is the measurement problem still a thing? More recently however, I have gained the impression that a lot of people regard decoherence as the solution to this problem, but I have also seen specific claims that decoeherence does not attempt to resolve the measurement problem at all. When I first was introduced to QT we were taught around the formalism of the Copenhagen interpretation (vague and unsatisfactory concepts of observations/measurements with a totally arbitrary line-in-the-sand between quantum and classical) and it was my understanding that the so called, "Measurement Problem" was still one of the big unsolved problems in physics. I understand that this is still very much an active area of research but it seems to me that there is a general belief that decoherence is some sort of holy grail? So take this all with a grain of salt.I am trying to better understand the current scientific consensus (to the extent that such a thing exists) on the interpretation of quantum physics.
#Quantum coherence decoherence free
In what I wrote above I tried to give an intuitive view as free as possible from such interpretations, but I guess some of my personal views have leaked in. What this means intuitively and physically, though, is not clear at all (that's the "measurement problem") and it is at this point that QM interpretations enter the dance. So in which sense is decoherence the "loss" of coherence? Formally, in the sense that interfering terms in the description of the system as a superposition of states vanish. It is precisely because the system behaves as many different systems interfering all together that its description is in some sense similar to a parallel computation.ĭecoherence can be seen as the manifestation of the rest of the world: not being isolated anymore, the quantum system loose its weird freedom, and behave like a proper disciplined classical one. This is where coherence is important for quantum computing. But it seems that this structure is much more free to "explore" its potentialities of evolution. Moreover, there is still consistence in the way properties are linked together: the system (which ultimately is nothing else that the ensemble of all properties needed to describe it) does not loose its structure. This coexistence is a non-trivial mathematical relationship that allows phasing and dephasing, like in wave mechanics (hence the wave-particle duality idea). Instead, the different values a property can take kind of coexist as long as the property is not measured.
In QM, it seems that when such properties are not involved in a too "intense" (again, not a well-defined concept here) interaction with the rest of the world, when they do not manifest themselves in a measurable way, we just cannot assume that they have definite values at all. These properties have well defined values at all time, whether they manifest themselves in a measurable way or not. The point is that in the classical world (to be short, this is the world as seen by physics before QM, let's say the 19th century world), a physical system is a set of actual objects that have definite properties like positions and momenta. Several of the words I used have a problematic or non-trivial meaning. I don't know if the previous sentence is intuitive enough, this is after all a very technical question.
This makes the system behave, well, non-classically. Quantum coherence is the coexistence (in a rather badly defined sense of "existence") of several non-exclusive quasi-classical descriptions of a physical system, which are all "existing" together in such a way that they produce interference effects.
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