E.C.G. Sudarshan (1931-2018)

Newsletter of the APS Division of Quantum Information

E.C.G. Sudarshan (1931-2018)

May 28, 2018 Articles 0

Professor E.C. George Sudarshan passed away Monday, May 14, 2018. He was born in Kerala, India in 1931. After receiving his PhD from the University of Rochester in 1958, where he worked with R.E. Marshak, he held professional positions at Harvard University, the University of Rochester, the University of Berne, Syracuse University and the University of Texas at Austin. He also had positions at the Indian Institute of Sciences in Bangalore and the Institute of Mathematical Sciences in Chennai.

He was well-known for several ground-breaking results in physics, including several that many believe should have shared the Nobel prize. He and Marshak were the first to propose the vector-axial vector theory which was the basis for the electro-weak interaction theory. He proposed the theory of coherent states in quantum optics and he also proposed, with Misra, the quantum Zeno effect. All three of these, in different areas, were likely worthy of a share of the Nobel prize in Physics according to many professionals in these fields. It was his lack of recognition for his work on coherent states by the Nobel committee that drew the most criticism. Beyond even these outstanding achievements however, he also proposed the existence of tachyons and described their consistency with relativity; he described the relationship between spin and statistics; and he contributed a great deal to the theory of open quantum systems.

For quantum information theorists, perhaps this latter work is most important. First, it is notable that Sudarshan, Matthews and Rau proposed dynamical maps in 1961 including what is now often called the Kraus decomposition. Kraus himself refers to that paper in his lecture notes. These lecture notes are presumably the origin of the name. Second, Gorini, Kossakowski, and Sudarshan provided a description of the semi-group master equation that is now often called the Lindblad equation. These two are the basis for much of our descriptions of the evolution of open quantum systems.

Professor George Sudarshan was my PhD supervisor, so I have many personal stories about his analogies, insight, and wisdom. (He is perhaps the one person I have met in my lifetime who I would describe as wise.) For example, he was able to understand a great deal about a subject by looking carefully at one fairly simple example. This is not something many of us can do, but his ability to generalize from one example or simple equation was astounding. In addition, he was often able to boil down a complex problem into a simple set of principles or concepts. This is shown in the 1961 paper mentioned above. He was also willing to tackle controversial problems or problems that other people would not consider. I once asked him about negative probabilities and he told me about one of his papers from the early 1960s. Many people would have thought my question was strange or ridiculous.

One particular story really stands out for me. Once I was trying to understand a paper I was reading and he walked by my office. I decided to ask him if he understood what the paper was about. He took the paper from me and went to his office. After about 2 minutes, he came out and said, “this is just about the invariance of spin through 4 pi rotations.” It was masked in a great deal of notation, however. So I asked, “Well, why didn’t they just say that?” He said, “Well it is very much like the cranes.” And he walked back into his office. Many of his students would have left that alone and just understood that this was Sudarshan. However, I was an annoying student who often asked the questions that others did not. Completely dumbfounded, I got up and followed him into his office and asked (in a way that showed I was clearly dumbfounded), “Cranes!? What cranes?!?!?!” He smiled a bit and told me this story. In a particular part of India, the cranes stand in the farmers’ fields. They come in the evening and sleep in the fields. In the morning, when the sun comes up, they go around and eat the seeds that the farmers had planted in the field the day before. So the farmers would sneak out at night and put a little pat of butter on their heads while they slept so that when the sun came up in the morning, the butter would melt, run into the cranes eyes so they could not see, and the farmers could catch them and kill them. I said, “OK, … but they are standing right there with the cranes sleeping. Why don’t they just kill them while they sleep?” He said, “Ahh, but that would be too easy.” So I understood that the paper said something easy, but made it difficult to understand so that it would sound more impressive. I think we all know that this happens more often than we would like in science. However, it was not Surdarshan’s way to state something in that way. I, for one, very much appreciated that, particularly since what he did was stretch my imagination with a clever analogy that I will never forget.

Professor Sudarshan, some believe, had some frustration since he did not receive the recognition that he truly deserved for many outstanding accomplishments by receiving a Nobel prize. I rarely saw any part of that. What I saw, was a very wise man who very much enjoyed that sense of discovery and also sharing his insight with others. I am very grateful to have shared that with E.C.G. Sudarshan, and I believe we should all be grateful for his contributions to our understanding and descriptions of the physical world.


Mark Byrd is the former secretary-treasurer for the GQI and DQI and currently a Professor of Physics at Southern Illinois University at Carbondale.


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