Congratulations to the Winners of 2022 Nobel Prize in Physics

The Nobel Prize season has arrived amidst crises─ war in Ukraine, disruptions in energy and food supplies, the fallout from the covid-19 pandemic, the climate crisis, and whatnot─ yet, the world’s most prestigious prize commands the attention of the whole world, and rightfully. As the dates neared, all the eyes turned towards the Royal Swedish Academy of Sciences for their announcements.   

The first two announcements covering the fields of medicine and physics have indeed pleased many. Let me first take you around the physics prize, for that metaphysical- phenomenon-like quantum entanglement and its resolution by the Laurates is pretty interesting to know.

First thing first: this year’s Nobel Prize for physics has been awarded to the trio:

Alain Aspect from Universite Paris-Saclay in France,

John Clauser from JF Clauser & Associates in the US, and

Anton Zeilinger from the University of Vienna, Austria

“for [their ground-breaking] experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science”, who shall share the prize money of 10 mn Swedish Kronor (US $915000) equally.

Next, comes the obvious question: what are those experiments carried out by these Laurates and what did they tell us? Before addressing it, let us first take a look at Quantum mechanics and its quirkiness.

Our Physics textbooks of school days told us that by using the equations given in it we can predict exactly how things will behave in the macroscopic world. But in the world of quantum (a state that physicists invented to describe sub-atomic systems), nothing is known for certain. For instance, we never know exactly where an electron in an atom is located. We only know where it might be. Everything in it is a probability. For example, the quantum state of an electron describes all the places one might find it, together with the probabilities of finding it at those places.

Another unique feature of quantum states is that they can be correlated with other quantum states. It means measurement of one state can affect the other quantum. This phenomenon of intimate linkage between two sub-atomic particles that are even separated by billions of light years of space is called: ‘quantum entanglement’. Because of this linkage, a change induced in one will affect the other. Schrodinger, the physicist who first coined the word, ‘quantum entanglement’, said entanglement is the most essential aspect of quantum mechanics.

However, this bizarre, counterintuitive phenomenon of instantaneous entanglement of particles that are even placed on opposite ends of the galaxy, failed to convince Einstein. For, this phenomenon cannot be explained by stating that the particles are mysteriously communicating with each other, since such communication needs to be faster-than-light communication to create an instantaneous effect. But it is simply forbidden by Einstein’s special theory of relativity.  Thus emerged EPR paradox, which Einstein dubbed as “spooky action at a distance”. And, perhaps lead by this paradox, Einstein felt, quantum theory was incomplete. He even believed that elements connecting the variables of one particle to another─ which he named, “local hidden variables” ─will eventually be found.  

In 1964, John Stewart Bell came up with a theoretical test proving that certain quantum correlations, unlike all other correlations in the universe, cannot arise from any local cause. He thus ruled out the existence of any ‘hidden variables’ that Einstein and a few other physicists believed to have a role to play in the phenomenon of quantum entanglement. This breaking of local realism was referred to as “the violation of Bell inequalities”.

It is from here that the work of the present laureates began. All three of them carried out experiments to test Bell’s theorem experimentally to establish that quantum mechanics is complete.

John Cluser, an American theoretical and experimental physicist, along with a UC Berkeley graduate student, Stuart Freedman (who, unfortunately, died in 2012), carried out an experiment for the first time to hunt for the violation of Bell inequalities in 1972. They sent two entangled photons in opposite directions toward fixed polarization filters.  The results obtained clearly violated Bell’s inequality. It thus proved that quantum mechanics cannot be replaced by a theory that uses hidden variables.

There, however, remained a few loopholes after Clauser’s experiment. To rule it out, Alain Aspect, a physicist from the University of Paris-Saclay, came up with a new experimental setup in 1982. He could manage to switch the measurement settings after an entangled pair had left its source. Thereby, he succeeded in proving that the setting that existed when the photons were emitted could not affect the result, i.e., the violation of Bell’s inequality.  He could thus prove that there are no hidden variables dictating the other entangled particle to behave just as the first particle did.  

In 1997 Anton Zeilinger, the third laureate moving a step ahead demonstrated the transference of quantum information from an entangled pair to a third particle. His group also demonstrated the possibility of quantum teleportation, a phenomenon of moving a quantum state from one particle to another at a distance. His work has indeed shown the possibility of linking a series of entangled systems together to build a quantum equivalent of a network.

As Anders Irback, Chair of the Nobel Committee for Physics said, the trio’s work with entangled states thus not only answered fundamental questions about the interpretation of quantum mechanics but also paved the way for a new kind of quantum technology to emerge.

The first application that strikes the mind when you think of quantum entanglement is cryptography. A sender and a receiver can build a secure communication link through entangled particles by generating private keys. These keys can then be used to encode their messages. If someone intercepts the signal and attempts to read the private keys, the entanglement breaks, since measuring an entangled particle changes its state. This enables the sender and the receiver to know that their communication has been compromised. 

Another application that comes to mind is quantum computing. When a large number of entangled particles work in concert, it becomes feasible to solve large, complex problems. A quantum computer with just 10 qubits can exhibit an equivalent amount of memory as 2^10 traditional bits.

Thus, the pathbreaking experiments of the trio opened up a new field of science and technology called Quantum Information Science (QIS) that has applications in computing, communication, sensing and simulation.

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