A solitary electron in free space is not a fixed particle at rest in a given inertial frame of reference. It is always oscillating in a simple harmonic motion (SHM) in its own electromagnetic inertia field, even at zero kelvin temperature. A Newtonian particle exhibits uniform motion in a straight line. A quantum particle like the electron exhibits uniform motion along a sine wave path. This explains the physical concept of the wave-particle nature of the electron. As the mass of a quantum particle increases, the wavelength of the particle decreases as per French physicist Louis de Broglie. In the limiting case the sine wave becomes a straight line. Also, a hypothetical electron without an electric charge is like the bob of a simple pendulum without a string. In an electron-spin qubit, the electron can oscillate either clockwise or anti-clockwise and cannot oscillate both clockwise and anti-clockwise at the same time. It cannot be both spin-up and spin-down at the same time.