Context

• The Nobel Prize committee decided to honour three scientists Alain Aspect of France, John Clauser of the US, and Anton Zeilinger of Austria for their work in domain quantum physics.

What is the contribution of these three scientists?

• Together, these three have made seminal contributions to not just the foundations of quantum theory but also to efforts that have now enabled the possibility of a wide range of applications.
• Their experiments have conclusively established that the ‘entanglement’ phenomenon observed in quantum particles was real, not a result of any ‘hidden’ or unknown forces.

What is the Significance of this Discovery?

• Wide applications: It could be utilised to make transformative technological advances in computing, hack-free communications, and science fiction-like concept of ‘teleportation’.

What is Quantum Theory?

• Subatomic level: Quantum theory is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles.It is the foundation of all quantum physics including quantum chemistry, quantum field theory, quantum technology, and quantum information science.
• Different from conventional physics: Quantum mechanics differs from classical physics in that energy, momentum, angular momentum.

Development in Quantum Theory so far

• Planck’s assumption: In 1900, Planck made the assumption that energy was made of individual units, or
• Albert Einstein’s theory : In 1905, Albert Einstein theorized that not just the energy, but the radiation itself was quantized in the same manner.
• Louis de Broglie theory: In 1924, Louis de Broglie proposed that there is no fundamental difference in the makeup and behaviour of energy and matter; on the atomic and subatomic level either may behave as if made of either particles or waves. This theory became known as the principle of wave-particle duality: elementary particles of both energy and matter behave, depending on the conditions, like either particles or waves (wave-particle duality).
• Heisenberg proposed: In 1927, Werner Heisenberg proposed that precise, simultaneous measurement of two complementary values – such as the position and momentum of a subatomic particle – is impossible. Contrary to the principles of classical physics, their simultaneous measurement is inescapably flawed; the more precisely one value is measured, the more flawed will be the measurement of the other value. This theory became known as the uncertainty principle, which prompted Albert Einstein’s famous comment, “God does not play dice.”

What is Entanglement?

• Entanglement was another of several weird properties exhibited by these tiny particles. Two particles, having ‘interacted’ with each other at some stage, were found to have got ‘entangled’ in a way that the behaviour of one produced an instantaneous reaction in the other even if the two were no longer connected in any way and were separated by very large distances.
• The entanglement property to open up new technological possibilities. first time that it was possible to ‘teleport’ the quantum states of a particle to another location without the particle moving anywhere and without a medium.

What is Superposition?

• It’s a phenomenon where, a particle exists simultaneously at multiple locations, known as superposition. The chance of finding the particle at any given place was dictated by probabilistic calculations, and once it was found, or observed, at one location, it ceased to exist at all other places.

What was the Einstein’s assessment?

• Special theory of relativity: Einstein’s Special Theory of Relativity prohibited any signal from travelling faster than the speed of light. The seemingly instantaneous communication due to entanglement had the danger of further unravelling the foundations of physics.
• Spooky behaviour: Einstein describes the strange behaviour by quantum particles as ‘spooky’.
• Speed of light: One major concern of Einstein, that entanglement allows for transmission of information at speeds faster than light, was not entirely accurate.When an operation is performed on one of the entangled particles, there is an instantaneous reaction in the other.
• Communication problem: There is no way for the observer at the other end to know the reaction has happened. The observer has to be made aware of the operation having been performed, and this happens only through classical communication channels limited by the speed of light restriction.

Conclusion

• The entanglement property is now being utilised to build the next generation of computers, called quantum computers, which exploit the quantum behaviour of particles to overcome challenges considered as unsurmountable. It is being used to create secure communication algorithms that would be immune to hacking.

Mains Question

Q.What is the quantum theory? How it is different from classical theory of physics? How entanglement property is used in various applications?

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