# NEC demonstrates solid step forward for quantum devices

- 20 February, 2003 08:40

Researchers at NEC have made a breakthrough in quantum computing that brings closer the realization of powerful computers that make today's most advanced machines look like pocket calculators.

The researchers have succeeded in getting a pair of quantum bits, or qubits, connected together in such a way that they act as a single entity, the first time that this has been demonstrated with solid-state qubits, NEC said.

Details of the research, which was led by Tsai Jaw-Shen, a research fellow at NEC's fundamental research laboratories, appear in Thursday's edition of the British scientific journal Nature.

Qubits are the quantum equivalent of the classical bits which operate in conventional computer systems today. They have a number of exotic properties which hold out the eventual promise of a completely new level of computing power once the extremely difficult technical problems are overcome.

In the NEC experiment, the single pair of qubits was held for just one-millionth of a second in a state known as quantum entanglement, which is key to achieving quantum computing.

Among the startling properties of qubits is that they do not just hold either binary 1 or binary 0, but can hold a superposition of the two states simultaneously. As the number of qubits grows, so does the number of distinct states which can be represented by entangled qubits. Two qubits can hold four distinct states which can be processed simultaneously, three qubits can hold eight states, and so on in an exponential progression.

So a system with just 10 qubits could carry out 1,024 operations simultaneously as though it were a massively parallel processing system. A 40-qubit system could carry out one trillion simultaneous operations. A 100-qubit system could carry out one trillion trillion simultaneous operations.

"A quantum computer of 100 bits could solve in a millisecond a problem that it takes the Earth Simulator to solve in 100 million years," said Tsai referring to a supercomputer built by NEC that is currently the world's most powerful computer.

At present, Tsai said, researchers don't see quantum computing as replacing all types of computer because it is only viewed as being suitable for factorization, which has immediate application in the area of code breaking.

Most modern encryption systems rely on the inability of current computers to factorize extremely large numbers which serve as encryption keys. The inherent massively parallel processing properties of quantum computers could render this task trivial, scientists believe.

"Every government is looking at this because of the military and financial security implications by realizing this kind of computing," said Eiichi Maruyama, director of the Frontier Research System at Japan's Institute of Physical and Chemical Research (RIKEN), which partially funded NEC's research. He said such quantum computers will be much cheaper than classical computers and, according to some researchers, could become a practical proposition any time between 10 and 30 years from now.

Looking ahead, Tsai said his next task is to try to extend the time that the qubits are in quantum entanglement. Beyond that, he is looking into constructing a logic gate, one of the basic building blocks of a computer system, using qubits.