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In quantum entanglement, two particles share a single state: measure one and you can predict what the same measurement on the other will show, however far apart they are. Yet no usable message passes between them, so entanglement cannot be used to send anything faster than light.

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In 1935 Albert Einstein, Boris Podolsky and Nathan Rosen used entanglement to argue that quantum theory must be incomplete, and Einstein later called it ‘spooky action at a distance’. In 1964 the physicist John Bell showed how experiments could settle the question: if particles carried hidden instructions fixed in advance, the agreement between measurements could only be so strong. From the 1970s onwards, experiments by John Clauser, Alain Aspect and Anton Zeilinger found stronger agreement than that limit allows, and the three shared the 2022 Nobel Prize in Physics. The link still cannot carry a message, because each side on its own sees only random results; the agreement shows up only when the two sides compare their lists of results by ordinary means, such as a phone call or the internet. Entanglement is now used in quantum encryption and quantum computers.

Türkçe oku
Kuantum dolanıklığında iki parçacık tek bir durumu paylaşır: Birini ölçtüğünüzde, aralarındaki uzaklık ne olursa olsun, aynı ölçümün ötekinde ne sonuç vereceğini önceden bilirsiniz. Yine de aralarında kullanılabilir bir mesaj gidip gelmez; bu yüzden dolanıklıkla ışıktan hızlı hiçbir şey gönderilemez.

Albert Einstein, Boris Podolsky ve Nathan Rosen 1935'te dolanıklıktan yola çıkarak kuantum kuramının eksik olduğunu savundu; Einstein daha sonra bu bağa “ürkütücü uzaktan etki” dedi. Fizikçi John Bell 1964'te sorunun deneyle nasıl çözülebileceğini gösterdi: Parçacıklar önceden belirlenmiş gizli talimatlar taşısaydı, ölçüm sonuçları arasındaki uyum belli bir sınırı aşamazdı. 1970'lerden başlayarak John Clauser, Alain Aspect ve Anton Zeilinger'in deneyleri bu sınırı aşan bir uyum buldu; üç fizikçi 2022 Nobel Fizik Ödülü'nü paylaştı. Bu bağ yine de mesaj taşıyamaz, çünkü iki taraf da kendi başına yalnızca rastgele sonuçlar görür. Aradaki uyum ancak iki taraf sonuç listelerini telefon ya da internet gibi sıradan bir yolla karşılaştırınca ortaya çıkar. Dolanıklık bugün kuantum şifrelemede ve kuantum bilgisayarlarda kullanılıyor.

Sources and further reading

Background reading: Quantum entanglement
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