A quantum computer was a computer that used phenomena from quantum mechanics such as superposition and entanglement. This was the ultimate computer.
(Note: The background section of this page uses most of the same words from the spintronics page of Terra Futura to save time.)
The story of the computer is the story of the shrinking switch. The earliest electronic computers such as the ENIAC used vacuum tubes as switches. The ENIAC was a mainframe computer which was so large it fit an entire room or more. During World War II, President Roosevelt wanted something smaller and more efficient than a vacuum tube. Finally, in 1947, the transistor was invented. Early transistors used germanium, but in 1954, they started using silicon. As transistor shrunk farther, there came a tyranny of numbers. The solution came from two men named Jack Kilby and Robert Noyce. It was the integrated circuit. Robert Noyce, of course, would become one of the founders of Intel along with Gordon Moore who predicted that transistors would shrink in half every two years. This led to the invention of the microprocessor and the personal computer. Of course, Moore's Law was not going to last forever. A replacement for silicon was needed.
With 22 nm, Intel decided that continued shrinking would only work for so long. The scientists there were determined to push silicon to the absolute limit. One of the main goals for Ivy Bridge was to have as much current as possible in the "ON" state and as close as possible to zero in the "OFF" state and to switch rapidly between the two states. The solution was to replace the two-dimensional stream with one or more three-dimensional fins. This was the tri-gate transistor. Power consumption was reduced by 50%, and speed was increased by 37 %. The tri-gate transistor was obviously more efficient than a conventional planar transistor. The tri-gate transistor would become the dominant form of transistor up until 2022 when silicon transistors reached 5 nm and could be shrunken no more. They were replaced with other semiconductors such as carbon nanotubes and graphene.
Carbon Nanotube Field-Effect Transistors (CNTFETs for short) were first tested in 1998 as a replacement for silicon should Moore's Law ever have broken down. Carbon nanotube transistors had many advantages. They had better control over channel formation than tri-gate transistors. The threshold voltage was better, too. So was the sub-threshold slope. Carbon nanotube transistors also had high mobility, high current density, and high trans-conductance. They were faster than tri-gate transistors by far. It was carbon nanotube transistors that helped bring virtual retinal displays into the mainstream along with graphene transistors. Carbon nanotube transistors brought a revolution to the computer industry. Computers were faster than ever before. Ultimately, however, this, along with other computer technologies, would be replaced with quantum computers. The process by which quantum computers brought an end to all was hastened by spintronics.
Spintronics had been experimented with since the 1980s. By 2012, the best results were by IBM at more than one nanosecond. That was not enough, of course. Over the course of the second decade of the 21st century, shielding and error-correction became better, eliminating the problem of EMP and making the computer better. Advances in the use of carbon nanotube and graphene transistors made spintronics even more common. Electrons no longer needed to be pumped in and out of the transistor's barrier layer. Therefore, the clock-rate was higher. Processors started using spintronics for processing. Computer memory used spin-based memristors to store data. Eventually, this would give rise to quantum computers.
Tech Level: 10-11
One of the main problems with creating a quantum computer was decoherence. Interactions with the external environment could cause it to decohere. Until 2011, the record for a calculation by a quantum computer was 3 X 5 = 15. This changed when D-Wave One was released. D-Wave One was an adiabatic quantum computer that solved the problem of decoherence with quantum annealing. Lockheed Martin was the first company to jump on the bandwagon. Later innovations would make quantum computers even better. These included new discoveries in the laws of physics as well as the incorporation of spintronics into quantum computers. By 2037, most government agencies, universities, and research institutes had quantum computers. Quantum computers were faster and more efficient than any computer that came before. Not only that, but they were the most secure. The quantum computer's encryption techniques were virtually unbreakable because of how many instructions that were needed to break the codes. It would take advances in nanotechnology to bring quantum computers to the level of consumer products. By then, the quantum computer would change the world.