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Quantum PC, a new step forward

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Quantum PC, a new step forward

Japanese researchers have announced that they have developed a new technology that allows the implementation of a small quantum circuit (see figure below), which could constitute the basis of the construction of a real computer .

The results of the joint effort of NEC, Institute of Physical and Chemical Research (RIKEN) and the Japan Science and Technology Agency (JST), were published in the latest issue of the journal Science.

One of the fundamental problems that research must address in the realization of quantum computers is decoherence: due to the interaction with the environment or with other parts of the circuits, qubits (the equivalent of bits, basic information of digital electronics) tend to alter their state and be unusable . Transferring information from one qubit to another can be complex: at the end of the operation, which until now included a direct connection between the two elements, the state of both is changed, preventing further steps.

Japanese scientists have come up with it instead a new three-stage system which eliminates the problem: thanks to the adoption of a third qubit, which acts as a temporary archive, and controlling the system with microwave pulses, they managed to drastically reduce the time required when the operation is carried out, completing it successfully.

A qubit is not limited to the usual 1 and 0 states of digital electronics, it also adds a “superposition” state which is somehow equivalent to zero and one at the same time. The Japanese circuit up to now has been able to copy the “superposition” state from one qubit to another, while it is not yet able to perform other operations .

Tsai Jawshen at the head of the team that deals with the project on behalf of NEC, said he was enthusiastic about the results obtained so far: not only their system has complied with all forecasts during the experiments, but its design makes it extremely scalable . The researchers hope to be able to develop a five-stage system by the end of the year, likely to implement some basic logic functions.

This is not the first success in this field: last December the team of researchers at the University of Berkeley led by John Clarke he had published, again in the pages of Science, the results of similar studies on the control of a pair of qubits. The approach of the Americans was however different and, by admission of Clarke himself (consulted by Wired), the Japanese circuit may have some advantages in the management of the decoherence factor.

The realization of a real quantum computer is still a long way off. At the moment, the best implementation is the one presented last February by D-Wave System, which incorporates 16 qubits: it will take many more to exceed the current capabilities of a supercomputer but, if the promises are respected, these machines will be one day able to outperform the processing capacity of any traditional device .

Luca Annunziata