  State disturbance by a quantum measurement is at the core of foundational
quantum physics and constitutes a fundamental basis of secure quantum
information processing. While quantifying an information-disturbance relation
has been a long-standing problem, recently verified reversibility of a quantum
measurement requires to refine such a conventional information trade-off toward
a complete picture of information conservation in quantum measurement. Here we
experimentally demonstrate complete trade-off relations among all information
contents, i.e., information gain, disturbance and reversibility in quantum
measurement. By exploring various quantum measurements applied on a photonic
qutrit, we observe that the information of a quantum state is split into three
distinct parts accounting for the extracted, disturbed, and reversible
information. We verify that such different parts of information are in
trade-off relations not only pairwise but also globally all-at-once, and find
that the global trade-off relation is tighter than any of the pairwise
relations. Finally, we realize optimal quantum measurements that inherently
preserve quantum information without loss of information, which offer wider
applications in measurement-based quantum information processing.
