Quantum computer - What's so great about it? Full-scale operation of Japan’s first machine (2/2)

Recently NHK News on-line reported the following:

量子コンピューター 何がすごい？国産初号機が本格稼働 (2/2)

2023年3月27日 20時03分

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実用化に向け競争激化

量子コンピューターは1980年代に概念や原型となるアイデアが提案され、1994年にはアメリカの研究者が量子コンピューターを使って暗号技術に用いられる巨大な数の素因数分解を高速で行える計算方法を発見し、注目されました。

日本では、理化学研究所のチームを率いる中村泰信センター長らが1999年に「量子ビット」を世界で初めて電気回路として作ることに成功。

従来の電気回路と同様に「量子ビット」を扱えるようになったことで、量子コンピューターの研究開発は加速し、現在では同様の「量子ビット」を使ってIT大手のグーグルやIBMなどが実用化を目指し、開発競争で世界をリードしています。

国内では、このほか東京大学や大阪大学、自然科学研究機構などもそれぞれ仕組みが異なる「量子ビット」を考案し、研究開発を進めています。

ノイズと温度 技術的な壁も

世界で開発競争が進む量子コンピューター。

超高速の計算を可能にするのは「量子ビット」の「重ね合わせ」ですが、実用化に向けた最大の課題は、この状態が電磁波や熱などといった「ノイズ」に非常に弱く、正確な計算ができるかどうかが周辺の環境に大きく依存する点です。

理化学研究所の量子コンピューターの場合「量子ビット」からなる集積回路は、動作を安定させるために、円筒形の容器で何重にも覆って「ノイズ」を遮るとともに、「絶対零度」と呼ばれる氷点下273度近くに保ちます。

ところが、「ノイズ」は「量子ビット」から電気信号を読み出すケーブルや、回路上の不純物などからも生じ、誤作動につながる場合があります。

そこで、誤作動による誤りをあらかじめ検知し、訂正しながら計算する「誤り訂正」の仕組みが考案されています。

「量子ビット」が1つの場合、「誤り訂正」を確実に行うには理論上、その1万倍の「量子ビット」が必要だと考えられています。

去年、433量子ビットの量子コンピューターを完成させたIBMはことし1121量子ビットの開発を計画していますが、実用化には少なくとも100万量子ビットが必要だということです。

量子コンピューターの計算能力を左右する「量子ビット」を増やすには、その数に応じた制御や信号の読み出しを行う大量の通信ケーブルだけでなく「絶対零度」に近い環境を保つ大型の冷凍機が必要となります。

創薬や金融、材料開発など、社会のさまざまな分野で具体的な問題の解決に導く可能性を秘めた量子コンピューターですが、超高速の計算を可能にするにはこれらの課題を乗り越えられるかがカギで、さらなる進化を遂げられるか、注目されます。

松野官房長官「大きな一歩」

松野官房長官は27日午後の記者会見で「量子コンピューターは国際的にも開発競争が激化しており、国産初号機は将来の実用化に向けたわが国の大きな一歩だ。今後、産学官によって広く活用され、産業、研究の発展に大きく貢献していくことを期待している。政府としては量子技術の実用化・産業化に向けた方針や実行計画を示す新たな戦略を去年10月から検討しており、これを着実に進めていく」と述べました。

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Intensifying competition for commercialization

Quantum computers were proposed as concepts and prototypes in the 1980s, and in 1994, American researchers using quantum computers, discovered a calculation method that could perform high-speed prime factorization of huge numbers used in cryptography, and that drew attention.

In Japan, in 1999, Dr. Yasunobu Nakamura (中村泰信), the head of the RIKEN team, succeeded in making a "qubit" as an electric circuit for the first time in the world.

Since it became possible to handle "qubits" in the same way as conventional electric circuits, research and development of quantum computers had accelerated, and now the same "qubits" were used by major IT companies such as Google and IBM, and led the world in the development competition.

In Japan, other institutions such as the University of Tokyo, Osaka University, and the National Institutes of Natural Sciences had devised “qubits” with different mechanisms and were progressing with research and development.

Noise and temperature - technical barriers

Quantum computers were the subject of intense development competition worldwide.

It was the superposition of qubits that enables ultra-high-speed computation, but the biggest challenge for practical use was that this state was extremely vulnerable to noise such as electromagnetic waves and heat, and whether it can be calculated depends greatly on the surrounding environment.

In the case of RIKEN's quantum computer, an integrated circuit consisting of "qubits" would be covered with many layers of cylindrical containers to block "noise" in order to stabilize the operation, and kept to near 273 degrees below freezing point, the so called “absolute zero”

However, "noise" was also generated from the cable that read out the electrical signal from the "qubit", and also arose from impurities in the circuit, etc., and that could lead to malfunction.

Therefore, an "error correction" mechanism had been devised that could in advance detect errors due to malfunctions, and perform correction while doing calculations.

In for one "qubit", it was theoretically believed that 10,000 times more "qubits" would be required to reliably perform "error correction".

IBM, which completed a quantum computer with 433 qubits last year, plans to develop 1121 qubits this year, but at least 1 million qubits would be required for practical use.

In order to increase the number of "qubits" that the computing power of quantum computers depended on, it would need not only a matching large number of communication cables that control and read out signals, but also a large refrigerator to maintain an environment close to "absolute zero".

Quantum computers had the potential to solve specific problems in various fields of society, such as drug discovery, finance, and materials development. The key to enabling ultra-high-speed calculations would be to overcome these issues, and attention would be paid to whether further evolution might be achieved.

Chief Cabinet Secretary Matsuno - ``A big step''

At a press conference on the afternoon of the 27th, Chief Cabinet Secretary Matsuno said, ``The development competition for quantum computers is intensifying internationally, and the first domestically produced machine is a big step for Japan toward future practical use. Based on industry-academic-government, it is expected that quantum technology will be utilized and contribute greatly to the development of industry and research. Since October last year, the government has been considering a new strategy that indicates policies and action plans for the practical application and industrialization of quantum technology, and we are doing this steadily.”

So, RIKEN (理化学研究所) has developed the first Japanese quantum computer that can be used by researchers. Japan is feeling the intensifying development competition for quantum computers internationally, and is developing action plans for the practical application and industrialization of quantum technology.