Heisenberg’s uncertainty principle is, without any doubt, one of the most profound statements in modern quantum physics. It states that pairs of certain properties of a quantum particle cannot be measured with arbitrary accuracy - for instance position and momentum. This is often justified by the notion that every measurement necessarily disturbs the quantum particle, which affects the results of any further measurements. This, however, turns out to be an oversimplification: the uncertainty is partly rooted in the quantum nature of the particle itself. Quantum particles cannot be described as point-like objects with a well-defined velocity. Instead, quantum particles behave like waves, which in general cannot be assigned an exact position. Consequently, a generalized uncertainty principle taking both kinds of uncertainty into account, that is from the measurement process and from the quantum behavior, was developed in 2003 and experimentally tested for the first time by us using neutrons. The present research project is aimed to further investigate these uncertainty relations with neutrons.
The second topic of the research projects are so called weak values, which are obtained in an experimental procedure usually referred to as weak measurements. The basic idea behind weak measurements is to gain very little information about the observed system, by keeping the disturbance on it, caused by the measurement process, (negligible) small. Weak values have a lot of useful applications. In our case they can be utilized to completely characterize, or more precisely, to reconstruct the state of a quantum system, or express error and disturbance for measurement uncertainty relations, which is also foreseen in the research project.
These two phenomena are investigated with neutrons by applying a well-know neutron optical tool, namely the neutron interferometer. Neutron interferometry is based on the wave nature of neutrons. If neutrons are isolated from the atomic nucleus, for example in the fission process of a research reactor, they behave like waves. This is usually refereed the as wave-particle duality. Inside the interferometer partial wave-function of the sub-beams in the individual interferometer paths are created and recombined coherently afterwards, resulting in interference effects. The resulting high sensitivity makes the neutron interferometer perfectly suited for investigations of uncertainty relations and weak values.
