Von Neumann was the first to establish a rigorous mathematical framework for quantum mechanics, known as the Diracvon Neumann axioms, with his 1932 work Mathematical Foundations of Quantum Mechanics. After having completed the axiomatization of set theory, he began to confront the axiomatization of quantum mechanics. He realized, in 1926, that a state of a quantum system could be represented by a point in a (complex) Hilbert space that, in general, could be infinite-dimensional even for a single particle. In this formalism of quantum mechanics, observable quantities such as position or momentum are represented as linear operators acting on the Hilbert space associated with the quantum system.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): What paper did von Neumann produce in 1932?
Mathematical Foundations of Quantum Mechanics