  An upper bound between the information gain and state reversibility of weak
measurement was first developed by Y. K. Cheong and S. W. Lee [Phys. Rev. Lett.
109, 150402 (2012)]. Their results are valid for arbitrary d-level quantum
systems. In light of the commonly used qubit system in quantum information, a
sharp tradeoff relation can be obtained. In this letter, this tradeoff relation
is experimentally verified with polarization encoded single photons from a
quantum dot. Furthermore, a complete traversal of weak measurement operators is
realized, and the mapping to the least upper bound of this tradeoff relation is
obtained. Our results complement the theoretical work and provide a universal
ruler for the characterization of weak measurements.
