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Ordinary computers store information in bits that are either 0 or 1. Quantum computers use qubits, which can be in a combination of 0 and 1 at once, called a superposition, until they are measured. For certain problems, such as simulating molecules, they could be far faster than any ordinary computer.

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In 1982 the physicist Richard Feynman suggested that computers built on quantum physics could simulate nature far more efficiently than ordinary ones. In 1994 the mathematician Peter Shor showed that a large quantum computer could break some of the encryption that protects the internet today, which drew wide attention to the field. The hard part is building one. Qubits are extremely fragile: heat or vibration can easily upset their state, a problem called decoherence, so some machines are cooled to about 0.02 degrees above absolute zero, the lowest temperature possible. Today's quantum computers are still small and make many errors, and they are not faster at everyday tasks such as browsing the web or sending email. Researchers hope they will help design new medicines, materials and batteries.

Türkçe oku
Sıradan bilgisayarlar bilgiyi bitlerle saklar; her bit ya 0'dır ya 1. Kuantum bilgisayarlar ise kübit kullanır: Bir kübit, ölçülene kadar aynı anda 0 ile 1'in bir bileşimi olabilir. Buna süperpozisyon denir. Molekülleri modellemek gibi bazı işlerde kuantum bilgisayarlar, sıradan bilgisayarlardan çok daha hızlı olabilir.

Fizikçi Richard Feynman 1982'de, kuantum fiziğine dayanan bilgisayarların doğayı sıradan bilgisayarlardan çok daha verimli biçimde modelleyebileceğini öne sürdü. Matematikçi Peter Shor 1994'te, büyük bir kuantum bilgisayarın bugün interneti koruyan bazı şifreleri kırabileceğini gösterince alana ilgi hızla arttı. Asıl zorluk, böyle bir makineyi yapabilmektir. Kübitler son derece hassastır: Isı ya da titreşim onların durumunu kolayca bozar. Buna dekoherans denir. Bu yüzden bazı makineler, ulaşılabilecek en düşük sıcaklık olan mutlak sıfırın yalnızca 0,02 derece kadar üstüne soğutulur. Bugünkü kuantum bilgisayarlar hâlâ küçüktür, çok hata yapar ve internette gezinmek ya da e-posta göndermek gibi günlük işlerde daha hızlı değildir. Araştırmacılar bu makinelerin yeni ilaçlar, malzemeler ve piller tasarlamaya yardım etmesini umuyor.

Sources and further reading

Background reading: Quantum computing
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In 1984 and 1985, John Clarke, Michel Devoret and John Martinis showed that a whole electrical circuit on a chip, cooled almost to absolute zero, can behave as a single quantum object, just like an atom. The discovery earned them the 2025 Nobel Prize in Physics.

The experiments were done at the University of California, Berkeley, in Clarke's group; Martinis was his doctoral student and Devoret a postdoctoral researcher. Absolute zero, −273.15 °C, is the lowest temperature possible. At the heart of the circuit was a Josephson junction: two superconductors, metals that carry current with no resistance when very cold, separated by an insulating layer only a few atoms thick. Vast numbers of electrons moved together as if they were one particle. The team saw two signs of quantum behaviour: the circuit escaped from a trapped state by tunnelling, slipping through an energy barrier it could not climb over, and it absorbed microwave energy only in fixed steps, or quanta, as an atom does. Circuits of this kind are now the qubits, the basic units of information, in the superconducting quantum computers built by companies such as Google and IBM.

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