In this chapter, we discuss probabilistic automata that realize all features of quantum mechanics.We start with quantum mechanics for a two-state system or a single qubit. The quantum spin in an arbitrary direction is associated with a corresponding classical Ising spin. For the quantum subsystem, the deterministic evolution for the automaton results in the unitary evolution according to the von Neumann equation for the quantum density matrix. Suitable updating rules can realize an arbitrary Hamiltonian for a single qubit. Quantum mechanics for a single qubit is the extension of the quantum clock system to rotations in three-dimensional space or on the two-dimensional sphere.