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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.

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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.

Türkçe oku
John Clarke, Michel Devoret ve John Martinis 1984 ve 1985'te, bir çipteki elektrik devresini mutlak sıfırın hemen üstüne kadar soğuttular ve devrenin tıpkı bir atom gibi, bütünüyle tek bir kuantum nesnesi olarak davranabildiğini gösterdiler. Bu buluş onlara 2025 Nobel Fizik Ödülü'nü kazandırdı.

Deneyler Kaliforniya Üniversitesi Berkeley'de, Clarke'ın ekibinde yapıldı; Martinis onun doktora öğrencisi, Devoret ise doktora sonrası araştırmacıydı. Mutlak sıfır (−273,15 °C), olabilecek en düşük sıcaklıktır. Devrenin kalbinde bir Josephson eklemi vardı: çok soğukken akımı hiç dirençsiz ileten iki süperiletken metal ve aralarında yalnızca birkaç atom kalınlığında yalıtkan bir katman. Devredeki sayısız elektron, tek bir parçacıkmış gibi birlikte hareket ediyordu. Ekip, kuantum davranışının iki işaretini gördü. Devre, hapsolduğu durumdan tünelleme denen olayla, yani aşamayacağı bir enerji engelinin içinden sızarak kurtuldu. Mikrodalga enerjisini de tıpkı bir atom gibi yalnızca belirli paketler, yani kuantumlar hâlinde soğurdu. Bugün bu tür devreler, Google ve IBM gibi şirketlerin süperiletken kuantum bilgisayarlarında kübit, yani temel bilgi birimi olarak kullanılıyor.

Sources and further reading

Background reading: Superconducting quantum computing
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