99 percent reliability: Silicon quantum computers achieve practical usability

Researchers have high hopes for the development of quantum computers. The background: The smallest computing units – here called qubits – cannot only assume the state 1 or 0. Instead, several intermediate states are also possible. This in turn makes it theoretically possible to carry out even complex arithmetic operations in the shortest possible time. So far, however, quantum computers have only been able to actually operate faster than classic supercomputers in individual cases. This is due to difficulties with the qubits already mentioned. The quantum computers that have been used commercially to date either rely on superconducting quasiparticles or on ions trapped in magnetic traps. However, this also has disadvantages. On the one hand, this makes the qubits comparatively large. On the other hand, they are quite unstable. As a rule, they remain stable for a maximum of 100 microseconds – which leads to a comparatively high error rate. So far it has not been possible to have more than 127 qubits work together permanently.

Image: Tony Melov / UNSW

Reliability must be over 99 percent

Recourse to the technology of classic computers could help here. Because theoretically it is also possible to construct quantum computers based on silicon. Particularly stable and small qubits could be used here. In tests in the laboratory, a single such computing unit could be kept stable for around 35 seconds. This is an extremely good value and could represent a breakthrough in quantum computing. So far, however, research has been stuck in a dead end. Because individual qubits achieved a reliability of 99.9 percent. But as soon as you combined several of them, the error tolerance dropped to below 99 percent. However, according to the current definitions, correct calculation is no longer possible. The individual computing units therefore offered a lot of potential, but could not be combined into a larger computing system. At least until now. Because now three research groups have developed silicon-based quantum circuits that bring the required reliability with them.

Different approaches led to success

The basic approach was quite similar for the individual teams: they all used magnetic fields to control the behavior of the qubits. However, there were differences in the details. One team relied on an additional electron that operates between the qubits and thus brings the two phosphorus qubits into harmony with each other. The other groups used electrons in a matrix of germanium-enriched silicon. In this way, a correct cooperation of two qubits could be made possible. In all three cases, the quantum computers then had to calculate standardized algorithms in order to test the susceptibility to error. The result: With values ​​between 99.35 and 99.65 percent, decisive improvements may have been achieved. Even then, individual errors will still occur. However, the number is so small that a targeted correction can be made in each case. This means that silicon-based quantum computers are ready for practical use, at least in theory.

Via: Nature

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