In 2001, a team of physicists from IBM and Stanford University in Silicon Valley revealed that they had built a remarkable computer capable of exploiting the strange rules of quantum mechanics to process information.
This quantum computer was designed to factorise numbers, a problem that conventional computers have particular trouble with. The team proudly demonstrated it by finding the two prime factors of the number 15 (3 and 5, in case you were wondering).
That was an impressive feat. It was possible because a quantum object can exist in two states at the same time, representing a 0 and 1 simultaneously. This kind of superposition allows one quantum object to compute with 2 bits simultaneously, two quantum objects to compute with four bits simultaneously, eight quantum objects to compute with 256 bits and so on.
The IBM/Stanford had just seven qubits at its disposal. But the promise from these kinds of devices is huge: a computer with just 30 qubits would be more powerful than any existing conventional computer.
But in the ten years since then, nobody has built a quantum computer much more powerful than this. How come?
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