Observation of nonadditive mixed state phases with polarized neutrons

TL;DR

This paper experimentally investigates mixed state phases in polarized neutrons, demonstrating that geometric and dynamical phases do not simply add up in mixed states, highlighting fundamental quantum phase behavior.

Contribution

It provides the first experimental evidence that in mixed states, geometric and dynamical phases do not sum to the total phase, unlike in pure states.

Findings

Geometric and dynamical phases are experimentally measured in neutron polarimetry.

Sum of individual phases differs from total phase in mixed states.

Pure states show additive phase behavior, mixed states do not.

Abstract

In a neutron polarimetry experiment the mixed state relative phases between spin eigenstates are determined from the maxima and minima of measured intensity oscillations. We consider evolutions leading to purely geometric, purely dynamical and combined phases. It is experimentally demonstrated that the sum of the individually determined geometric and dynamical phases is not equal to the associated total phase which is obtained from a single measurement, unless the system is in a pure state.