Undergraduate research and publications

by Nelson Christensen

The participation of undergraduates in scientific research is important for a number of reasons. First and foremost, undergraduates can make significant contributions to the science. In addition, research by undergraduates is now recognised to be an extremely important part of the educational process for these students. LIGO and Virgo have provided wonderful opportunities for undergraduates to experience the joys of physics  research. With guidance, students across the undergraduate physics spectrum can find a project suited to their level of expertise and their interests.


Professor Nelson Christensen, who has conducted research and published with numerous undergraduates over the years.

Over the years at Carleton College I have had the thrill of seeing many students make real and significant contributions to LIGO and Virgo’s research efforts. When the students take their success from the classroom to research their joy for physics really springs out. But it should be noted that research is not a sure success for all undergraduate physics majors. I have seen “A” students who could never make the connection to the independent and original work required with a research project; that’s okay, research is not for everyone. On the other hand, I have worked with students who earned B’s and C’s in their physics classes, yet exploded with the opportunity of research; the applied nature of the physics motivated them, and consequently, often encouraged them to become better students in the classroom as well.


Duo Tao, Carleton College senior, seen in front of the Goodsell Observatory. Duo has been conducting gravitational wave research for three years while at Carleton, and has been an author on eight papers.

In this paper (Optimizing signal recycling for detecting a stochastic gravitational-wave background) in Classical and Quantum Gravity the first author, Duo Tao, is a Carleton College senior. He has been participating in LIGO-Virgo research for three years. He started doing noise studies, namely trying to identify noise that would affect the search for a stochastic background of gravitational waves, or gravitational waves from pulsars. Duo has had great success with this work, and became known in the parts of the LIGO Scientific Collaboration and Virgo Collaboration that worry about these sorts of signal searches. Duo’s excellent research earned him authorship on a number of collaboration papers where his contributions were significant.

A year ago I wanted to set out on a new project, and it seemed to be a good opportunity to challenge Duo with a very different type of physics study. For this work Duo had to really learn about the stochastic gravitational wave background, and how it can be detected. Then he had to completely understand how gravitational wave interferometers work, especially with advanced concepts like signal recycling. This was a lot to ask of an undergraduate. However, Duo tore into the subject, first acquiring the background, then in calculating the performance of the interferometers under different configurations. Duo conducted all of the calculations in this paper, then wrote the initial draft of the paper. Over the year I had the good fortune to see Duo evolve from a student to a colleague.

Duo’s observation of the process is the following:
“I started doing LIGO-Virgo research with Professor Nelson Christensen as a sophomore. I discovered not only to apply what I learned in class to research problems, but also to think actively in order to answer research questions. This study on the signal recycling system began in the winter of my junior year. In this project, we find the optical configurations of the signal recycling system that give the best sensitivity for detecting a stochastic gravitational waves background. It shows that if we apply the optimal signal recycling configuration, we might be able to improve the limit of the energy density of the stochastic background by an order of magnitude lower.

Personally, the research experience as an undergraduate is very valuable to me. On one hand, I have been fortunate to conduct intellectually inspiring research in a supportive environment. On the other hand, internally, I get a lot of intellectual satisfaction from research. We once had some mysterious fluctuations in the relation between the laser power and the sensitivity limit. In order to figure out its nature, I studied the quantum noises of the interferometers in great depth. It feels great to have the motivation to learn and think actively, and the motivation is the source of a lot of intellectual satisfaction.”

I have also seen my colleagues at Carleton College producing excellent research and publications with undergraduates; see these recent examples (1, 2, 3, 4). Quality undergraduate research is not just succeeding at small liberal colleges, but at major universities as well. This is a great plus for undergraduate physics education.

It is also amusing for me to see how the success of undergraduate research is passing onto the next generation. A former star undergraduate researcher at Carleton College, Michael Coughlin, is now a postdoc at Caltech. However, he now routinely keeps a look-out for good students at his alma mater, and attracts them into new research projects. This recent paper (Optimizing searches for electromagnetic counterparts of gravitational wave triggers) was led by Michael and Duo.

Finally, many times I have been paid a high compliment – “Nelson, that graduate student of yours is really doing great work.” I love to then reply, “No, that’s my undergraduate!” Good luck with your undergraduate researchers!

Nelson Christensen is the George H. and Marjorie F. Dixon Professor of Physics at Carleton College, but has now transitioned to Nice, France to be the director of the Artemis Laboratory at the Observatoire de la Côte d’Azur.

Duo Tao is a senior physics major at Carleton College, and will start physics graduate school at Caltech in the fall of 2018.


“Optimizing signal recycling for detecting a stochastic gravitational-wave background”, by Duo Tao and Nelson Christensen, 2018 Class. Quantum Grav. 35 125002  doi.org/10.1088/1361-6382/aac148 

  1. “Superconducting-Gravimeter Tests of Local Lorentz Invariance”,
    by Natasha A. Flowers, Casey Goodge, and Jay D. Tasson, 2017 Phys. Rev. Lett. 119, 201101 doi.org/10.1103/PhysRevLett.119.201101
    by J. M. Weisberg and Y. Huang, 2016 ApJ 829 55 doi.org/10.3847/0004-637X/829/1/55
  3. “Effects of varying interfacial surface tension on macroscopic polymer lenses”,
    by Charlotte Zimmerman, Mason White, and Martha-Elizabeth Baylor, 2015 Opt. Eng. 54(9) 097108 doi.org/10.1117/1.OE.54.9.097108
  4. “Entanglement and its relationship to classical dynamics”, by Joshua B. Ruebeck, Jie Lin, and Arjendu K. Pattanayak, 2017 Phys. Rev. E 95, 062222 doi.org/10.1103/PhysRevE.95.062222

“Optimizing searches for electromagnetic counterparts of gravitational wave triggers”
by Michael W Coughlin, Duo Tao, Man Leong Chan, et al., 2018 Monthly Notices of the Royal Astronomical Society, sty1066 doi.org/10.1093/mnras/sty1066

This work is licensed under a Creative Commons Attribution 3.0 Unported License.