Matter cannot occupy, as per classical physics, the same space at the same time. However, in particle physics, particles like atoms and sub-atomic particles like electrons and light behave differently and can exist in more than one state at the same time. The field called quantum mechanics had contributions from Planck, Bohr and Einstein. Light could exist as a wave and particle, depending on how it is seen.
Quantum mechanics allows two or more particles to exist in entangled state. What happens to one particle in the entangled pair determines what happens to the other. Distance between them does not matter. Einstein attributed this co-ordination to hidden variables which he called ‘spooky action at a distance.’
John Bell in the 1960s came to the conclusion that rather than hidden variables, the co-ordination between entangled pair could be attributed to chance element. It occurs while measuring the characteristics of one of the particles. Bell developed a mathematical inequality. It states had there been hidden variables, the correlation between results of a great number of measurements would not exceed a certain value. Quantum mechanics proved this to be false, as there are results which exceed this value.
Alain Aspect, John Clauser and Anton Zeilinger have been awarded 2022 Nobel in physics for their pioneering work in Quantum mechanics. They have built on Bell’s work.
Clauser from the US started work way back in 1969, and is still alive to receive the prize. He conducted an experiment by passing entangled photons through polarisation filters to test Bell’s inequality. The experiment violates Bell’s inequality. It confirms there are no hidden variables at work. It is governed by quantum mechanics. The experiment of Clauser had some flaws — the measurements were fixed. It thus could not have detected the hidden variables.
Aspect a French physicist, eliminated this bias by varying measurement settings only after the entangled photons left their source. Thus the experimental set-up would not tell upon the results.
Zeilinger, an Australian physicist, used more than two entangled particles. These now become the foundation of quantum computation. These entangled particles could be manipulated. He discovered quantum teleportation — here the particles assume unknown quantum characteristics different from other particles over long distances.
Zeilinger envisages quantum communication all over the world.
Quantum physics is the study of matter and energy at sub-atomic level. These are the smallest building blocks of nature. The subject goes against the usual ideas of cause and effect and the nature of reality.
Quantum entanglement could be a stepping stone for a whole new technology. Transistors and lasers are the products of first quantum revolution. The ability to manage and manipulate systems of entangled particles will provide the researchers the tools to create quantum computers, build quantum networks and secure quantum communication.