Vietnam Success Story

Nguyen Thi Kim Thanh is a senior researcher at the Institute of Physics of the Vietnam Academy of Science and Technology. She is also an ICTP Regular Associate. Earlier this year she received the prestigious Ta Quang Buu Award from the Vietnamese Ministry of Science and Technology that honors scientists who have reached outstanding achievements in basic research.

The award was attributed to Nguyen for a paper she wrote jointly with Mikhail Kiselev, a senior research scientist in ICTP’s Condensed Matter and Statistical Physics section. The article, titled “Thermoelectric transport in a three-channel charge Kondo circuit”, was published in Physical Review Letters in 2020. The study theoretically investigates the three-channel charge Kondo model.

Nguyen visited ICTP for a month in 2024 as part of her associateship, and she kindly agreed to talk about the prize and what it means for her career. 

What is the article that earned you the 2024 Ta Quang Buu Awards about?

The article is about charge Kondo, a variation of the conventional Kondo effect explained by the Japanese physicist Jun Kondo back in the 1960s. The Kondo effect is a phenomenon observed in metals doped with magnetic impurities: differently from what happens in pure metals, because of the magnetic interaction between conduction electrons and the spin of the impurities, at low temperatures the resistivity of the material increases with decreasing temperatures. Interestingly, phenomena similar to the conventional Kondo effect may be observed also in the absence of magnetic degrees of freedom, whenever degenerate quantum states are coupled to a continuum. For instance, the charge Kondo effect concerns the degeneracy of the charge states. One of the most prominent experimental implementations of the charge Kondo effect involves quantum dots, which are small, confined systems where electrons are restricted in all three spatial dimensions, leading to quantized energy levels.

How did you decide to work on this project?

I have been working on the theory behind the charge Kondo in collaboration with Mikhail Kiselev since I started my postdoc at ICTP.  Strikingly, in 2015, the group of Frédéric Pierre at Université Paris-Saclay managed to successfully implement the charge Kondo effect in their experiments. This breakthrough opened the way to observational studies of the multi-channel Kondo effect, which occurs when a quantised degree of freedom, the spin or the charge, is coupled with multiple electron continua, all independent from one-another.
In 2017, I participated in an international conference on “Nanophysics, from fundamental to applications: reloaded” in Quy Nhon, Vietnam, where Frédéric Pierre talked about the three-channel charge Kondo effects that he observed in his experiments. Analytical results for the two-channel Kondo effect were already available and I became very interested in developing a theory for the three-channel Kondo effect, which is precisely what we describe in the paper.

How did you find the final result?

The most important thing about our result, in my opinion, is the way in which we went about finding the solution. Ever since that conference in 2017, I continued to think about the problem, all the while working on other projects. Then, one day, the idea came up to do a change of variables and use the Cartan algebra. When I told that to Prof. Kiselev, he was extremely excited, so I went on and performed the calculations. Of course, some other challenges came up along the way, as they always do, but the method worked.

The importance of your result is related also to its possible applications to quantum computing. Can you explain what the connection between the two is?

The charge Kondo circuit is a quantum simulator. The basic idea behind quantum computers is to start from a basic two-state quantum system, and to exploit the entanglement that is intrinsic in the quantum nature of the system. That is exactly what we also have in the charge Kondo circuit, which therefore can be considered a quantum simulator. Quantum simulators are essential tools to understand the physics behind quantum computers.

What role has your involvement with ICTP played in helping you achieve this milestone?

ICTP has been crucial, for this prize and for my career, as was my collaboration with Prof. Kiselev. We have been working together for 17 years now, it is him who introduced me to this topic when I first came to ICTP to do my postdoc. Everyone is very surprised when I talk about our long-term collaboration on a single topic, but it takes patience to achieve good results. Over the years, we have been able to stay in touch and to continue our work together also thanks to ICTP, which I visited many times as an invited researcher and as an Associate, first as a Junior Associate, between 2016 and 2021, and starting this year, as a Regular Associate.

What does this prize mean to you?

This prize means a lot to me. The purpose of the prize is to encourage and honor scientists who have made outstanding contributions to the natural sciences, and I think this is something that one can receive only once in a lifetime. It is a huge honor to be recognized for my work with such a prestigious award. Not only am I extremely happy, the award has also motivated me to study harder to obtain more important results in the future.

I also hope that visibility associated with the prize will attract more young students to this topic. There are many interesting projects that I would like to work on. I am thinking about them, keeping them in one corner of my mind as I did with the three-channel charge Kondo model, we will see what ideas will come up!

Nguyen Thi Kim Thanh is a senior researcher (level II) at the Institute of Physics, Vietnam Academy of Science and Technology. She works in the field of condensed matter physics, more specific on thermoelectric transport in nanostructures in Kondo regime. She received her Ph.D. from the Centre for Theoretical Physics, University of Aix-Marseille II in France. Between 2007 and 2010 she was a postdoctoral researcher at ICTP, where she worked with Mikhail Kiselev on the charge Kondo physics. In 2010 she got a second postdoctoral position at the University of Cincinnati, in the United States. In 2013, she got a permanent position at the Institute of Physics of the Vietnam Academy of Science and Technology, where she still works.