Tracing the contributions of IISc scientists
Danish physicist Niels Bohr once had a visitor at his country cottage at Tisvilde. Seeing a horseshoe nailed above the front door, the visitor was amused and asked Bohr if he believed in the superstition that it brought luck. Bohr apparently replied: “No, I certainly do not believe in this superstition. But they say that it does bring luck even if you don’t believe in it!”
This tongue-in-cheek comment is a perfect analogy for quantum mechanics, a relatively new field of study born in the early 1900s. A central tenet of this field is that events at the quantum level can occur whether or not you can observe them directly, but if you observe them, they may not happen.
In contrast to the classical understanding of physics, quantum mechanics introduced two revolutionary concepts. The first one, proposed by German scientist Max Planck, was relatively easier to imagine: the amount of energy associated with any form of electromagnetic radiation is “quantised” – it is present in the form of small, discrete and countable packets called photons.
The second idea, introduced by French physicist Louis de Broglie, was that every object in the universe has a “dual nature” – it can behave like a particle sometimes and like a wave in other situations. This is why a highly energetic electron can behave like a billiard ball and collide with other electrons, producing X-rays, but it can also create diffraction patterns like a wave, a property used in electron microscopes to spot even tiny bacteria.
Over the past century, this concept of wave-particle duality, although controversial and fantastical, enabled a better understanding of how atoms work, led to the advent of technology – computers, mobile phones, television and so on – and inspired innovations in other areas like chemistry and biology.
Indian scientists, too, have made their fair share of contributions to quantum mechanics and its applications. They not only solved fundamental problems in the field, but also helped build infrastructure and create an ecosystem conducive to its growth. Research institutions like TIFR, RRI, and others emerged out of these efforts. Scientists at these institutes led many key advances in the field. The first of these happened exactly 100 years ago and involved the usual suspect – light.
Indian scientists solved fundamental problems in quantum mechanics, helped build infrastructure and created an ecosystem conducive to its growth
First light
In 1924, Satyendra Nath Bose, a Reader at Dhaka University, was studying the nature of photons when he came across something unusual. He investigated the idea that all photons are identical. This was significant because, until then, all known subatomic particles, like electrons, had different labels or “quantum numbers” unique to that particle. However, Bose’s calculations concluded that two or more photons can have the same exact set of labels, making them indistinguishable. Later, this turned out to be not just a photon-specific phenomenon but a generic property of a class of subatomic particles called bosons, named after Bose.
Unfortunately, his theory was not accepted by the scientific community until Einstein took notice and vehemently supported it. They jointly published a theoretical report on what they called Bose-Einstein statistics. “Though Bose’s ideas were experimentally verified only after 1980, his pioneering contribution was the first (theoretical) effort from an Indian to the development of quantum mechanics,” explains B Ananthanarayan, Professor at the Center for High Energy Physics (CHEP) at IISc.
A few years later, in 1928, CV Raman, a scientist at the Indian Association for the Cultivation of Science, Kolkata, showed for the first time that a light beam could scatter off molecules and produce a secondary beam with a wavelength different from the original one. This report, published in Nature, was a key experimental demonstration of the particle nature of light, which in turn validated both core concepts of quantum mechanics. Raman would go on to win the Nobel Prize in 1930.
With the Raman effect, India made its foray into the experimental side of quantum mechanics. Bose and Raman continued to lead the early quantum revolution in India well into the 1930s and trained many young researchers in the emerging field. However, the lack of quality research facilities was a constant struggle. The situation changed only in the 1940s when a young man, with a vision for nation building, arrived at IISc.
Cosmic connection
Bose and others soon realised that quantum mechanics was not just a theoretical concept but could explain many phenomena in the real world, from how electrons move to how materials deform.
In the years following his discovery, Raman, who became the Director of IISc in 1934, invited Homi J Bhabha to the Department of Physics. Bhabha joined as a Reader in Theoretical Sciences in 1938. Earlier, during his PhD at Cambridge, he had performed the first quantum mechanical analysis of particle-antiparticle collisions. This process, known as the Bhabha Scattering, is still one of the hallmarks of collider physics experiments.
Soon after joining IISc, Bhabha began experiments on cosmic ray showers – streams of high-energy particles travelling at extremely high speeds throughout the universe. The energies of these particles are large enough to cause particle-antiparticle collisions, just like those seen in particle accelerators at CERN. Bhabha set up a cloud chamber to track the motion of these particles and antiparticles, and a Geiger counter to count the number of particles and antiparticles generated from these collisions. The Cosmic Ray Research Unit in IISc, established by Bhabha, was instrumental in performing the first of such experiments in India.
Soon after joining IISc, Bhabha began experiments on cosmic ray showers – streams of high-energy particles travelling at extremely high speeds
Bhabha realised that Indian research institutions did not have sufficient infrastructure for advancements in nuclear and high-energy physics. At his request, the Tata Trusts, jointly with the Government of Bombay, funded the establishment of the Tata Institute of Fundamental Research (TIFR) in 1945 within the IISc premises. The Cosmic Ray Research Unit was absorbed into it.
Later that year, TIFR formally shifted to Bombay with Bhabha as its first Director. Within the next decade, TIFR was at the forefront of India’s nuclear and atomic programmes, carrying out balloon-based cosmic ray experiments, which resulted in the discovery of particles called K mesons and several cosmic ray isotopes.
Around 1960, for the first time, cosmic ray experiments in India went underground when BV Sreekantan, a student of Bhabha from his IISc days, and his TIFR colleagues conducted the historic Kolar Gold Field cosmic ray muon experiment. They observed the collision of cosmic ray particles with atmospheric neutrinos – mysterious particles that pervade the universe and hold clues to the origins of the universe. “The first atmospheric neutrino event was recorded at the Kolar Gold Fields,” says Ananthanarayan. “That is another fundamental discovery that came from India.”
While Bhabha was busy building infrastructure for experimental work, theoretical research languished. Some efforts, led by MN Saha, DB Bose and others, were happening at Calcutta University, Allahabad University and Banaras Hindu University. But theoretical quantum physics in India lacked a strong ecosystem – a problem that persisted until 1972.
Building infrastructure
In the late 1960s, Satish Dhawan, the then Director of IISc, invited ECG Sudarshan to spend a few weeks a year at IISc as a visiting researcher. Sudarshan, who had been a student at TIFR, was already famous for his work on quantum field theory (QFT) and particle physics. “Along with his thesis advisor Robert Marshak at the University of Rochester, Sudarshan developed the V-A theory, which was a universal framework for describing the mechanism underlying two fundamental forces of nature – electromagnetic and weak interactions,” says Ananthanarayan. Sudarshan also proposed a mathematical framework for the quantum description of light, called the “Sudarshan Representation” – this was crucial for the development of laser physics and quantum optics in the days to come.
In 1972, the Centre for Theoretical Studies (CTS) was established at IISc through the efforts of Sudarshan, DS Kothari and KP Sinha. “With CTS, Sudarshan’s idea was to create an environment similar to that at the Institute of Advanced Studies in Princeton, in which talented scholars from different fields would nucleate ideas and engage in interdisciplinary conversations,” recalls Ananthanarayan. CTS boasted experts in fields like environmental science, atmospheric sciences, biology, and high energy physics, and employed a rigorous theory programme for visiting researchers. Sudarshan’s student and collaborator N Mukunda, along with researchers like R Rajaraman, Romesh Kaul, J Pasupathy, and others, created a unique stronghold for pushing the frontiers of QFT.
CTS was a boost for quantum mechanics in particular. It also set the stage for the next set of advancements in an emerging area called condensed matter physics.
Condensing ideas
Soon after the birth of quantum mechanics, scientists realised that its principles could also be used to understand how assembling clusters of atoms can influence their collective physical, chemical and electrical properties. This field of science eventually came to be known as quantum condensed matter physics – the biggest contributor to modern-day technologies involving electronics and photonics. The semiconductor and nanotechnology revolutions were spawned by exploring the quantum nature of condensed matter.
Early experiments in this area by Raman’s student Krishnan focused on shining light on colloids – mixtures in which tiny particles remain dispersed within a different medium. After 1950, researchers at IISc started experimenting with semiconductors. With CTS, quantum condensed matter theorists also arrived at the scene. “In my opinion, serious, high-level quantum condensed matter theory started in IISc around the early 1970s when KP Sinha and Narendra Kumar joined,” says HR Krishnamurthy, Honorary Professor at the Department of Physics, IISc.
After 1950, researchers at IISc started experimenting with semiconductors. With CTS, quantum condensed matter theorists also arrived at the scene
Not just quantum condensed matter, Indian physicists also actively participated in establishing the field of soft condensed matter in which proteins, polymers, bacteria and other “soft” materials are put under the microscope. “In India, [research on] soft condensed matter was pioneered in the Liquid Crystals Lab at RRI,” says Sriram Ramaswamy, Honorary Professor at the Department of Physics, IISc. “They discovered new phases of liquid crystals.” Ramaswamy himself propounded the active matter theory, a framework which deals with micron-size particles attached to self-powered engines. This framework is so diverse that it can be used to understand the swimming motion of bacteria and even the flocking of migratory birds.
Chasing superconductivity
In 1909, Dutch physicist Kamerlingh Onnes discovered superconductivity in mercury – a property that allowed the material to conduct electricity with zero resistance at very low temperature (-269°C). Since then, scientists have been on the hunt for superconductivity in materials at higher and more reasonable temperatures.
Sinha was one of the first Indians to begin theoretical research in this area. While at Savitribai Phule Pune University, Sinha, along with N Kumar, showed that shining a pulsed laser on a superconductor can cause it to become superconducting at even higher temperatures. “Following the first experimental demonstration of high-temperature superconductivity by Bednorz and Muller, TV Ramakrishnan and I both became interested in this field,” says Krishnamurthy. Ramakrishnan worked on unique theoretical models to get a better understanding of the characteristics of high-temperature superconductivity. Krishnamurthy performed extensive calculations in a bid to understand various theoretical models of high-temperature superconductors.
Ramakrishnan also worked on theories focusing on the effect of adding impurity atoms to materials, including superconductors, leading to a material having small superconducting patches co-existing simultaneously with other non-superconducting patches. “Additionally, Ramakrishnan worked on freezing of classical liquids, and those ideas could be applied to colloidal suspensions too,” adds Ramaswamy. “He was one of those people whose range went across classical and quantum systems.”
Krishnamurthy, for his part, has also worked on a variety of other problems involving the quantum physics of models and materials with strong inter-particle interactions. These include models of manganite materials which show colossal magneto-resistance, ultra-cold atoms trapped in optical lattices, and so on. His work has also involved developing new theoretical techniques for addressing such problems.
To complement these theoretical advances, scientists like CNR Rao and Ajay K Sood joined IISc in the late 1970s and 1980s respectively, and started working with high-temperature superconductors and other cutting edge quantum materials. Rao made pioneering contributions to the field of materials and popularised the concept of solid-state chemistry, an interdisciplinary field that brings together material science and chemical synthesis, in India.
In 2025, the world will celebrate the International Year of Quantum Science and Technology to mark 100 years of the birth of quantum mechanics. Over this century, Indian scientists have left their mark in almost all branches of quantum mechanics, and continue to contribute to emerging areas like dark matter and dark energy. Quantum computing and quantum communication have captured the public’s imagination and attracted significant attention from the Indian research community and policymakers. If there is one thing that these developments have taught us, it is that the unknown often holds great promise, much like Bohr’s horseshoe.
Aniket Majumdar is an Integrated PhD student in the Department of Physics, IISc and a former science writing intern at the Office of Communications
