Our common understanding of the quantum measurement process is incomplete. On the one hand, quantum measurements are performed by the billions every day (every time an elementary particle leaves its traces in a detector at the Large Hadron Collider at CERN. a quantum measurement is being performed), and the results of these measurements have corroborated existing theory to an astonishing degree. On the other hand, many physicists will freely admit that they do not know what actually happens in such a measurement. The most widely used framework is the Copenhagen interpretation, which points that during a measurement, the quantum wave function (that might be in a superposition of states) collapses so as to to agree with the state of the measurement device. In that way, classical reality forces quantum reality to agree with it. However, this assumption has led to countless contradictions and paradoxes. Here we present a formalism that suggests that this collapse is an illusion, and that after measurement the wave function is still in a superposition, which now includes the observer. At the same time, the measurement device does not reflect the underlying quantum reality. In the worst case, the classical device reveals nothing about the underlying truth. In other words, classical devices lie about the underlying quantum reality. A formalism based entirely on quantum information theory allows us to reach those conclusions unambiguously, and suggests that experiments can tell apart theories that are based on a collapse picture, and others (such as ours) in which the underlying wave function does not collapse.
Our quantum-information-theoretic reformulation of the measurement process answers several of the most profound questions discussed in the literature:
-Is the reduction of the wave function real?
-Is quantum reality accessible via standard quantum measurements?
-What quantum protocols can reveal the nature of the quantum world?