Two-state quantum system
![Passing electrically neutral silver atom particles beam through Stern–Gerlach experiment's inhomogeneous magnetic field will split the beam into two beams, each corresponding to one of the possible spin values of the outermost electron of the silver atom .](/Images/godic/202502/18/Stern-Gerlach_experiment4520.PNG")
In quantum mechanics, a two-state system (also known as a two-level system) is a system which can exist in any quantum superposition of two independent (physically distinguishable) quantum states. The Hilbert space describing such a system is two-dimensional. Therefore, a complete basis spanning the space will consist of two independent states.