# Physics Spotlight

## Kun Chen

Kun Chen was nominated by Professor's Nikolay Prokofiev and Boris Svistunov for his many contributions to our UMass Amherst campus, as well as, his constant presence as a role model for students who would like a career in academia. Kun will defend his thesis in March. The Physics Department is very excited to see another student graduate from UMass Amherst and wish Kun the best of luck in his future endeavors at Rutgers where he has already landed a prestigious postdoctoral position. Congratulations and good luck Kun!

**What brought you to the University of Massachusetts to continue your studies?**

I started collaborating with Professor's Nikolay Prokofiev and Boris Svistunov as an undergraduate student. I really liked their style when it came to Science and was fascinated by their idea of searching Emergent Physics using a computer. So I decided to come to UMASS to explore more in depth.

**Where did you do your undergrad? What is your degree in?**

I received my Bachelor’s degree from University of Science and Technology of China.

**Who is your faculty advisor and why did you pick them?**

Prof. Boris Svistunov is my faculty advisor and Prof. Nikolay Prokof’ev is my academic advisor. They are specialists in the field that I am particularly interested in and they had a lot of experience working with students.

**What has been your favorite Graduate level course?**

I really liked Boris’ course “Superfluidity and Superconductivity”. It achieves a good balance between breadth and depth of knowledge, which is not easy for an advanced Graduate level course. Thanks to this course, my understanding of many-body physics has levitated to an entirely new level.

**What are some of your research interests?**

The main theme of my current research activities is controllable studies of emergent phenomena in strongly correlated quantum matter, which is one of the central challenges in modern Condensed Matter Physics.

In many-body systems, particles may cooperate through interactions, giving rise to a macroscopic collective state governed by a set of new physical laws that are very different from the microscopic equations of motion. These new physical laws describe collective degrees of freedom rather than underlying particles, thus overriding the relevance of microscopic details. This concept is known as emergence. It can bridge the atomic scales to the macroscopic scales of quantum matter, therefore playing a vital role in Condensed Matter Physics.

This is why the physics in Condensed Matter is so rich. Here is an interesting example: Under certain conditions, a cloud of ultracold atoms can behave like a “tinyverse” where the effective physical law is relativistic but with an extremely slow speed of “light” (about 10% of a snail’s speed).

**Has any of your research resulted in a published article?**

We studied the Higgs particle in the “tinyverse” which emerges from the ultracold atoms. This resulted in two publications (Phys. Rev. Lett. 110, 170403 (2013), Phys. Rev. B 92, 174521 (2015)). We also calculated some dynamical properties of this “tinyverse” to test our results against an AdS/CFT theory, which tries to use a quantum gravity theory to solve some notoriously hard condensed matter problems (Phys. Rev. Lett. 112, 030402 (2014)). Recently, we also find the ultracold atoms “tinyverse” can even support a quasiparticle with a fractional charge number (Phys. Rev. B. 94.220502 (2016)). Besides the ultracold atoms, we also studied another interesting “tinyverse” emerging from an 3D antiferromagnet, where we find the signals of “monople” excitations (Phys. Rev. Lett. 116, 177203 (2016)).

**What are your future plans? Is there a trend that you would like to see surface in your field of study?**

Recently, I have been developing a Monte Carlo method called DiagMC which aims to simplify the high order perturbation calculation. Currently, one of the mainstream approaches to strongly correlated quantum matter for theorists is inventing a mean-field theory, then waiting for numerics or experiment to test the mean-field predictions. I hope that in the near future, our DiagMC method can make high order perturbation calculations so cheap so that everybody can afford going beyond the mean-field calculation to make their predictions more controlled. Maybe one day, when a theorist wants to publish some mean-field results, the Referee will ask “Why don’t you test your mean-field theory with DiagMC?”.

**Do you have a favorite experiment that you have worked on thus far?**

Although I haven’t personally worked on it, I am really impressed by the LIGO experiment that detects the gravitational wave and the LHC experiment that finds the Higgs particle. For decades, scientists have been pursuing gravitational wave/Higgs particle which seemed to be impossible to observe with the technology at the time. I heard stories about this since I was a kid, but still, they kept pushing the technology to its limits in an attempt to achieve better accuracy or higher energy. Eventually, a “phase transition” happened and the eureka moment finally occurred. This is the pattern of making fundamentally important discoveries.

**What advice would you give to undergraduates considering Graduate programs?**

Think big, but start small.

**Do you have any hobbies?**

I consider myself a bit of a geek because I have many DIY hobbies. Feel free to check out the DIY acrobatic gorilla robot that my team and I made by clicking here.

## Physics Department