Like graphics chips, quantum computers can be seen as coprocessors and will not replace traditional computers, but complement them. Nevertheless, there are many potential fields of application, and hopes are high: Time-critical optimization problems faced by navigation and traffic control systems, for example, as well as AI, materials research and medicine: the simulation of molecules and proteins is difficult for classic computers, among other things because here quantum mechanical effects play a role. Quantum computers use precisely such effects for calculation – and can use them. This makes them much better suited for simulating such systems.
Two types of quantum computers are currently in widespread use: quantum annealing machines, which are specialized in optimization tasks, and universal quantum gate computers, which can perform arbitrary calculations. In both cases, the programming differs fundamentally from that of classic computers: In order for quantum physical effects to flow into the calculations, a quantum computer must differ from classic computers in terms of its fundamental components. Assumptions and experiences from their programming should therefore be set aside.
In contrast to classic bits, the state of a quantum bit, or qubit for short, is not either 0 or 1, but a mixture of these, called superposition, in which the base states 0 and 1 overlap. A qubit can therefore be “almost completely 0 and only a little 1”, “halfway 0 and 1” or “exactly 0”. The base states 0 and 1 are usually expressed with | 0⟩ and | 1⟩, pronounced “Ket 0” and “Ket 1”.
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