Title: Quantum Mechanics From Principle of Least Observability

Abstract: We show that the basic non-relativistic quantum formulations can be derived from a least observability principle. The principle extends the least action principle from classical mechanics by factoring in two assumptions. First, the Planck constant defines the discrete amount of action a physical object needs to exhibit during its dynamics in order to be observable. Second, there is constant vacuum fluctuation along a classical trajectory. A novel method is introduced to define the information metrics that measures additional observable information due to vacuum fluctuations, which is then converted to the additional action through the first assumption. Applying the variation principle to minimize the total actions allows us to elegantly recover the basic quantum formulations including the uncertainty relation and the Schr\"{o}dinger equation in both position and momentum representations. Adding the no preferred representation assumption, we obtain the transformation formulation between position and momentum representations. The extended least action principle shows clearly how classical mechanics becomes quantum mechanics. Furthermore, it is a mathematical tool that can bring in new results. By defining the information metrics for vacuum fluctuations using more general definitions of relative entropy, we obtain a generalized Schr\"{o}dinger equation that depends on the order of relative entropy. The principle can be applied to derive more advance quantum formalism such as quantum scalar field theory.