A computer in which the fundamental unit of information, called a quantum bit or qubit, is not binary but in a superposition of two states. This qubit property arises as a direct consequence of quantum mechanics in which the direction of an electron’s spin could be up, down, and also a superposition of up and down states. Thus a qubit can exist as 0, 1, or simultaneously as both 0 and 1, with a numerical coefficient representing the probability for each state. Quantum computers could be much faster than even the fastest current computer processors as each qubit can simultaneously hold values for a large number of parallel computations. To date, designs of quantum computers have involved ion traps, cavity quantum electrodynamics, and nuclear magnetic resonance to measure and manipulate the spin of individual electrons or atoms.

https://www.newscientist.com/article/2138373-google-on-track-for-quantum-computer-breakthrough-by-end-of-2017/ An article on the development of quantum computing, from New Scientist magazine