The difference between the quantum-mechanical world and the classical world that we experience in our daily life, is well illustrated by the process of quantum measurement. The problem of quantum measurement is as old as Quantum Mechanics itself, now approaching a century. A quantum system may have properties that are undecided until one makes a measurement of the system. In the quantum measurement, such an undecided property suddenly becomes stochastically decided, with certain probabilities for the possible outcomes. The problem is that this process has not yet been given a physical explanation. This situation has opened up for several extraordinary interpretations on how Quantum Mechanics works and how quantum measurement can be understood.
An essential question is whether the observed randomness in quantum measurement is inherent, i.e., whether there is a fundamental mechanism that stochastically determines the result. The alternative would be to show how quantum measurement could be described as a quantum-mechanical interaction between the measurement apparatus and the measured system, combined with a statistical analysis. In the latter case, a single measurement would be a deterministic quantum-mechanical process in which the unknown initial state of the measurement apparatus determines the result.
In their work, Karl-Erik Eriksson
and Kristian Lindgren
, professors at Physical Resource Theory, Department of Space, Earth and Environment, follow the latter path and identify a quantum-theoretical mechanism in which unknown microscopic details of the measurement apparatus influence the process. They demonstrate that this results in a bifurcation process in which the possible outcomes occur with the expected probabilities.
Until today the discussion on quantum measurement has primarily been carried out in Quantum Mechanics as it was used in the 1920s and in the 1930s, a theory that lacks reversibility in the form of inverse processes. With the development of Quantum Field Theory in the 1940s and 1950s, quantum theory became consistent with the Special Theory of Relativity and included reversibility. This meant a total change of the picture of what may happen in quantum mechanics, a fact that opens for the new approach by Eriksson and Lindgren. Thus the measurement problem can be solved within Quantum Mechanics itself without any modification or extension.
The present work is the continuation of a larger collaboration that has also involved Professor Erik Sjöqvist, Uppsala University, and Professor Martin Cederwall, also at Chalmers.
The research now proceeds with more detailed modelling of quantum measurement as a purely physical process with possible applications in, for example, nanotechnology.