Interview with Professor Dhananjay Mehendale, Head of the Electronics Dept. at S.P. College, Pune

Scientific theories are best supported by what might be called ‘surprising’ facts. That is, the theory makes a surprising conjecture and over time experiments are performed that bear it out. A famous example of this in quantum mechanics is De Broglie’s conjecture that matter, or particles, would exhibit wave-like properties. De Broglie made this conjecture in 1924 in his PhD thesis because light—long thought to be a wave—had recently (1923) been discovered by Compton to exhibit particle properties. De Broglie reasoned on the basis of a general symmetry in nature that particles would analogously be found to exhibit wave-like properties. His dissertation committee didn’t know what to do with his thesis and sent it to Einstein who approved it wholeheartedly. De Broglie’s conjecture was subsequently borne out in 1927 by an experiment performed by Germer and Davisson. De Broglie was awarded the Nobel Prize for Physics in 1929 making him the only person to receive a Nobel Prize based on his doctoral dissertation.

PJOP: Professor Mehendale, could you describe any similar instances of ‘surprising’ confirmation that you’ve come across personally as part of your research?

Prof. Mehendale: Yes. In fact one of my theories had a surprising consequence that I subsequently found out had been discovered by a physicist by the name of Eberly. This area is ‘hot’ because it is relevant to whether we could ever build a quantum computer that will be light years faster than the electronic computers of today.

In quantum mechanics two or more particles through interaction can become ‘entangled’ so that their properties are perfectly correlated or perfectly anticorrelated. An example of this is when one particle of the entanglement is observed as having what is known as an ‘up’ spin, the other particle will have a ‘down’ spin and vice versa. And this will happen instantaneously when one particle is observed, no matter how far apart the particles are. We don’t even have to observe the other particle. We can associate 0’s and 1’s with these states and the fact that one part of the system can be determined instantaneously without observing it is partly what makes quantum computers a possibility—the other part is that an entangled system, being in a superposition of several states, can be used to do parallel processing. While the particles are entangled and unobserved neither has an ‘up’ or ‘down’ spin; the particles are merely in a superposition of states like Schrodinger’s cat which is neither alive nor dead until someone observes it.

The possibility of using entanglements to instantaneously transfer information was acknowledged to face certain difficulties. For example, it was widely known that entanglements in the real world would degenerate due to environmental forces over time. But the degeneration was thought to be like exponential decay, with half the original amount remaining entangled after a period known as a half-life. This means the amount that could be used for instantaneous information transfer would diminish but some amount would be left over a long enough time-interval to make quantum computing possible.

But in 2004, Eberly and Yu published their results showing that entanglement may decrease abruptly to zero due to the influence of what is called ‘quantum noise’ from vacuum fluctuations. They called this non-smooth, finite-time decay, entanglement sudden death (ESD).

In 2008, I published a paper that proposed a set of mathematical conditions under which the entanglement could degenerate. I did this in ignorance of Eberly’s earlier paper. Eberly’s result most conspicuously came to light after he received an award for it in 2009, which was when I learned of it. Basically my idea was that if any pairs of rows or columns of the multimatrix representing the entangled state became proportional to each other—possibly due to the influence of quantum or classical noise—, the entanglement would degenerate and the observation of spin of one particle would have no bearing on the spin of the other particles. I didn’t say this in my article, but a consequence of the mathematical formalism was that pairs of rows or columns could become proportional suddenly making the associated multimatrix have rank 1, leading to what is now known as entanglement sudden death (ESD). Sudden Death is surprising because, as most people know, decay in nature is generally exponential, obeying a half-life law. My formalism provided an explanation of how this surprising result was possible.

PJOP: Congratulations on having developed the formalism, the theory if you will, that can account for this surprising discovery of ESD. Did you bring your theory to the attention of Eberly?

Prof. Mehendale: Yes I did. In 2009, I let Eberly know of my article. His response was to encourage me to devise experimental situations in which it could be verified that an ESD event occurred as a result of the relevant rows or columns becoming proportional. The experiment could even provide controls for preventing ESD, for preserving entanglement so that the dream of quantum computing could be achieved.

PJOP: Have you formulated any response to Eberly?

Prof. Mehendale: No. Actually in dealing with certain preoccupations at that time I totally forgot about this. Thank you for reminding me of this incomplete business. I will try my best to look into this issue at the earliest possible time.

PJOP: Thank you. We look forward to learning of your work. To change the subject, you know in preparing for this interview, I read that entanglement also makes teleportation possible. Could you talk a little about that?

Prof. Mehendale: Sure. Since entanglement can be used to instantaneously convey information, it could be used to convey all information about you to a distant star where there could be placed a machine that would receive the information and use it to reconstitute you. Unfortunately, there is something called the Anti-Cloning Theorem in quantum mechanics which prevents the exact duplication of any system. So for you to teleport instantly to the distant star, your body on Earth might have to be destroyed. This is a problem because it is not at all clear that your consciousness would be teleported along with all the physical information about you. So the teleportation machine could simply be an elaborate way to commit suicide.

PJOP: I guess that would make it very difficult to get travel insurance… That’s all the questions I had on this topic. Perhaps we can meet again to discuss other philosophically relevant topics in Physics or Mathematics. Thank you, Professor Mehendale for a most illuminating discussion.

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47 Responses to Interview with Professor Dhananjay Mehendale, Head of the Electronics Dept. at S.P. College, Pune

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