Quantum mechanics is a branch of physics that deals with phenomena at microscopic scales, describing the wavelike and particle-like behavior of energy and matter. Erwin Schrödinger developed the wave equation and Schrödinger equation, which provide a mathematical description of quantum systems. Werner Heisenberg, Max Born, and Pascual Jordan created an equivalent formulation of quantum mechanics called matrix mechanics, which is the basis of Dirac's bra-ket notation for the wave function.