In our latest polarimetric experiment 1 we a demonstrate a simple and precise tradeoff relation between correlation and disturbance of successive spin measurements a neutron polarimetric setup. The information gained through any quantum measurement inevitably causes a certain amount of disturbance on a subsequent measurement due to quantum incompatibility. This intrinsic feature is deeply embedded in the foundations of quantum mechanics and is identified to be a resource for achieving quantum advantages in various quan- tum communication tasks. Therefore, uncovering and characterizing different aspects of this property is highly important.
The correlation and the disturbance induced by quantum measurements are not independent quantities; they are mutually related in a nontrivial way. This relationship is expressed as covariant symmetry interplay between the two quantities. Exploiting these symmetries provides a robust tool for estimating characteristic parameters of measurement devices, such as sharpness and bias, with practical application in high-dimensional settings. Our experimental implementation efficiently demonstrates our theoretical findings, covariant trade-off. This is illustrated below for different mesurements strength of the second measurement, resulting indifferent radia of a quarter circle in the correlation-disturbance plane.
At a fundamental level, we propose that optimal configurations of disturbance, as a way of transmitting information, and correlation, as a measure of predictability, could outperform or even rule out certain classical (hidden variable) models. Associating a classical (noncontextuality) inequality within our scheme offers a perspective on the extent of nonclassicality implied by quantum uncertainties, which also aligns with schemes of two-time Leggett-Garg macroscopic realism, sequential random access codes, self-testing of measurement instruments, and sequential correlation measurements in Bell scenarios. Consequently, our scheme could be effectively adapted to optical-based communication tasks where quantum advantage over classical counterparts can be explored.
1. Ali Asadian, Florian Gams, and Stephan Sponarr, Phys. Rev. Res. 8, L012011 (2026). ↩