Large effects from quantum reference frames

Abstract Reference frames are used to parameterize measurements of physical effects, but since their practical realization uses material objects, they may affect observations performed in a combined quantum state of the measured system together with the frame. Here, a procedure is used that makes it possible to describe non-monotonic reference scales in a quantum treatment, revealing large quantum effects in the measured system whenever a reference frame encounters a turning point. Subtle quantum correlations in the combined state of system and frame, and more broadly the concept of relational quantum mechanics, can be tested via a characteristic and surprisingly large shift in the measured value.