Signifying quantum uncertainty relations by optimal observable sets and the tightest uncertainty constants

Quantum uncertainty relations constrain the precision of measurements across multiple non-commuting quantum mechanical observables. Here, we introduce the concept of optimal observable sets and define the tightest uncertainty constants to accurately describe these measurement uncertainties. For any quantum state, we establish optimal sets of three observables for both product and summation forms of uncertainty relations, and analytically derive the corresponding tightest uncertainty constants. We demonstrate that the optimality of these sets remains consistent regardless of the uncertainty relation form. Furthermore, the existence of the tightest constants excludes the validity of standard real quantum mechanics, underscoring the essential role of complex numbers in this field. Additionally, our findings resolve the conjecture posed in [Phys. Rev. Lett. 118, 180402 (2017)], offering novel insights and potential applications in understanding preparation uncertainties.