This study is the first experimental verification of the Landauer bound on a single spin, which is the smallest information carrier in size. We used four experiments (single spin experiment, giant spin experiment, nanomagnet experiment, and Stern-Gerlach experiment) to demonstrate that a single spin was much more energy efficient than other information carriers due to its small size and weak coupling with the surroundings. We conclude that quantum spintronics, with single spins as qubits, is an energy-efficient computing paradigm that requires the smallest amount of energy, close to the theoretical Landauer bound to perform computations.