The Wolf Prize winner in physics explains how the idea of composite fermions solved the mystery of the fractional quantum Hall effect, what the connection is between his theory and the experiments of Motti Heiblom and James Eisenstein, and why he took it upon himself to establish a new institute for theoretical physics in Mumbai.
Prof. Jainendra K. Jain, one of the leading theoretical physicists in the field of condensed matter, has won the 2025 Wolf Prize in Physics for his development of the theory of composite fermions and his contribution to the understanding of the fractional quantum Hall effect. The prize was awarded to him together with Prof. Mordechai (Motti) Heiblom of the Weizmann Institute of Science and Prof. James Eisenstein of the California Institute of Technology, for advancing the understanding of the surprising properties exhibited by two-dimensional electron systems in strong magnetic fields. The Wolf Prize is considered one of the most important international scientific awards, and many of its winners in physics have subsequently received the Nobel Prize.
Last week, the 2025 award ceremony was held in the Knesset, which was postponed due to the state of emergency that year. For the same reason, no winners were chosen and the 2026 award ceremony was not held.
Jain grew up in the town of Sambhar in the state of Rajasthan, India, near the Thar Desert. After his studies in India, he moved to the United States, completed a doctorate at Stony Brook University, and continued his postdoctoral research at the University of Maryland and Yale University. While working at Yale in the late 1980s, he conceived the idea of composite fermions. He then joined the faculty at Stony Brook, and in 1998 moved to Pennsylvania State University – Penn State – where he still works today. He is currently on partial leave from the university, alongside his new position in India.
A quantum phenomenon in a system containing countless electrons
“When we think about Quantum physics"We usually think of very small microscopic objects, for example a hydrogen atom," Jain said in an interview with the Al-Hadayan website. "But The quantum Hall effect "Shows quantum behavior in a macroscopic system containing a huge number of electrons."
The quantum Hall effect occurs when electrons are confined to two-dimensional motion and exposed to a strong magnetic field. Such systems are not just a theoretical idea: electrons actually move in two dimensions in thin layers of semiconductors, MOSFETs, and materials such as graphene.
In the complete quantum Hall effect, the Hall conductance does not vary continuously. It adheres to quantized values related to integers and fundamental constants of nature, and passes between them in steps. The values are almost independent of the sample size or shape, and can therefore be measured with extraordinary precision.
According to Jain, the complete quantum Hall effect was understood relatively quickly. To a first approximation, it can be described in terms of electrons that do not interact with each other, with their motion in a magnetic field creating discrete energy levels.
However, it was later discovered Fractional quantum Hall effectThis time, states related to fractions such as one-third and two-fifths appeared. These results could not be explained by independent electrons.
“It was clear that this was a liquid of electrons with very strong correlations,” said Jain. “But it was not clear how to describe this liquid, how to understand which fractions show up in experiments and which don’t, and what else is going on in these systems.”
An electron that “dresses” inQuantum vortices
Jain's solution was to change the perspective. Instead of trying to directly solve the complicated problem of many electrons repelling each other, he proposed describing new entities:Composite fermions.
In the quantum wave function, each electron is associated with an even number of quantum vortices. The connection is not mechanical, like two objects being connected to each other, but an expression of the coordinated structure of the entire system. The even number preserves the fermionic nature of the new particle. The combination of the electron and the vortices behaves as a quasiparticle – an emergent particle that emerges from the collective behavior of the system.
The vortices change the effective magnetic field experienced by the composite fermion. In some situations, the reduced field can be much weaker than the external field, and even zero on average. As a result, a complicated system of strongly interacting electrons can be described as a simpler system of composite fermions, the residual interactions between which are relatively weak.
“The fractional quantum Hall effect of electrons can be understood as the complete quantum Hall effect of composite fermions,” Jain explained. “We take a very complicated problem of strongly interacting electrons and map it to a problem of almost free composite fermions. In a sense, the effect of the interactions is swallowed up in the very birth of the composite fermions.”
The theory was able to explain why fractional Hall states appear in certain sequences and not in others. These sequences are now called “Jane sequences,” and the corresponding states are known as “Jane states.” The theory also made it possible to unify the complete quantum Hall effect and the fractional effect in a single framework.
Is the composite fermion a real particle?
One of the questions addressed to Jane was whether the composite fermion is an actual physical entity or just a convenient mathematical tool.
He says the distinction is not always clear. In principle, one could start with quarks and electrons and try to explain the properties of helium-4 using them. But to understand its superfluidity, a much more useful starting point is the helium-4 atoms themselves.
“At every level, we want to start with objects that interact relatively weakly,” he said. “When you take the composite fermions as a starting point, you can almost immediately explain a large part of the phenomena.”
One of the key predictions of the theory was that the composite fermions would sense a reduced magnetic field to a certain extent. Experiments have examined their motion and the paths they take, similar to tracking a billiard ball bouncing off the sides of a table, and the results have been consistent with this prediction.
“They are as real as Cooper pairs are real in superconductors, or as each particle emerges from another in a system of thickened material "It's real," said Jane. Cooper pairs are named after physicist Leon Cooper; there is no connection to copper.
Three winners – separate and complementary works
Although the prize was awarded to three researchers together, Jain emphasized that he, Heiblum, and Eisenstein did not work as a joint research team. Nor, he said, did the two experimentalists collaborate systematically. The connection within the framework of the prize reflects separate works that complemented each other and together expanded the understanding of quantum electron systems.
Eisenstein is known, among other things, for his research into two-layer electron systems, in which coherent states with properties reminiscent of superfluids can be created. Methods he developed made it possible to create separate electrical contact with each of the two layers and study the coordinated motion of electrons and holes. Jain said that he dealt with some of the theoretical issues related to these systems, but made it clear that this was not the main focus of his work.
Heiblom and his colleagues at the Weizmann Institute have performed key experiments to measure the fractional charge of the excitations in the fractional quantum Hall effect. Instead of the entire electron charge, the collective excitations in the system can carry only a fraction of it.
Jain also mentioned later experiments in which effective charges were sometimes measured to be two or three times larger than the basic fractional charge. He said he and his colleagues have been trying to provide theoretical insight into this in recent years.
“We don’t work on the same things,” he concluded. “Our works complement each other.”
Possible connection to quantum computing – but still far from implementation
The theory of composite fermions also has a possible connection to quantum computing, but Jane is careful not to present it as a direct application or as a technology that is already mature.
In certain states, composite fermions can form pairs, similar to electron pairs in superconductors. Theoretical suggestions suggest that such paired states may support exotic Majorana excitations.
The interest in Majorana excitations stems from the possibility of storing quantum information nonlocally. The information is not concentrated in a single point, and therefore it may be better protected from local disturbances. This is one of the proposals for building a topological quantum computer with built-in resistance to some errors.
Jain mentioned Microsoft's efforts to develop a quantum computing architecture based on Majorana states, but emphasized that this does not directly use the complex fermions of a coupled Hall system. He said the physics discovered in these systems has inspired the search for other implementations.
He also emphasized that the field is still far from a practical computer. Systems of one or more qubits have already been demonstrated in other technologies, but a convincing and acceptable demonstration of Majorana-based qubits and their entanglement still remains a challenge.
New assignment in Mumbai
In addition to his role at Penn State, Jain currently serves as the founding director of the Lodha Theoretical Physics Institute (LTPI), a new privately funded research institute located in Mumbai, India.
His return to India is not a complete break from American academia: the institute's official website notes that he is on partial leave from Penn State. He has been given another task – to build a theoretical research center in his home country that can be integrated among the world's leading research institutes.
“When I learned about the vision of Abhishek Lodha and the Lodha Foundation – to build an institution based on excellence and to be among the best in the world – that vision spoke to me deeply,” he said. “The fact that the institute is independent of government funds and is privately funded gives it a great deal of flexibility, which is difficult to achieve in government-supported institutions in India.”
The institute was inaugurated shortly before the interview and is still in its early stages. Jain said that at this stage he is the main permanent researcher, alongside students and colleagues who participate in the activity, but the intention is to gradually expand it.
He said that basic research in India is small relative to the size of the country. In the field of quantum condensed matter, he estimated, there are only about a hundred researchers working in India – a number much smaller than in the United States, China or Germany. These were his general estimates during the conversation, and not data from an official survey.
Jain hopes that the Lodha Institute will provide proof that it is possible to establish an international center of excellence in India, which will attract researchers and allow young people to engage in fundamental questions without encountering the bureaucratic constraints that sometimes characterize government institutions.
As an example, he mentioned the Motty Highbloom, who left IBM at the time and returned to Israel, and later helped build a strong research group in condensed matter physics at the Weizmann Institute.
“We hope to build something along those lines,” he said. “Setting up an experimental operation is much harder. We hope that in theoretical physics it will be a little easier, and that we can provide a proof of concept that this is possible.”
Herzog, the scientists and the brain drain
The discussion about Jain's return to India also connected to the question of brain drain. When I told him that the day before I had attended the event at the President's Office announcing the "Or" and "Bereshit" programs, which deal with the return of Israeli researchers from abroad, he compared it to the situation in India.
“I don’t understand why politicians in India are sensitive to this issue,” he said. “They have many other problems.”
Jane said that he was particularly impressed by the time that President Yitzhak Herzog devoted to scientists at the reception that preceded the Wolf Prize ceremony in the Knesset.
“He was there for the whole hour,” Jain said. “It’s something that probably wouldn’t happen in India – that politicians would spend so much time with scientists. I hope in the future it will happen here too.”
The comparison was not a criticism of a particular Indian leader, but rather an expression of his feeling that the political system in India still does not give basic research and attracting researchers the attention he would like to see.
“One humanity and one science”
Jain has visited Israel only twice. His first visit, he said, was a brief one-day visit about 25 years ago. This time he didn’t have much time to visit the labs, but he said he was well acquainted with the work of Israeli researchers in the field of quantum condensed matter. He mentioned Haiblum and other Israeli researchers, noting that many Indian physicists were trained in research groups in Israel.
“The Weizmann Institute is probably the best place in the world for this kind of research,” he said.
At the end of the interview, Jain also addressed the ability of science to cross national and political borders. The conference held to mark the inauguration of the new institute in Mumbai was attended by researchers born in various countries, including Israel and Iran.
“It never occurred to me for a moment that there was anything extraordinary about it,” he said. “In science, we are one group – one humanity and one science. Science should unite people, not separate them.”
More on the subject on the science website
- Winners of the 2025 Wolf Prize in Science and Architecture announced
- Wolf Prize in Physics for 2025: Recognition of quantum computing researchers, including Prof. Motti Heiblum of the Weizmann Institute
- The first nuclear clocks have begun ticking – opening a window to new physics
- Not a time machine: This is how researchers made a quantum system look like it was going backwards
- For the first time: Physicists quantum entangle the motion of atoms
