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Q&A: Nergis Mavalvala, MIT sciences dean and longtime LIGO physicist

29 November 2022

The MacArthur fellow’s efforts to minimize noise in gravitational-wave detection is yielding insights into the quantum behavior of macroscopic objects.

Nergis Mavalvala.
Nergis Mavalvala stands in front of the LIGO Advanced System Test Interferometer facility, where researchers develop and test LIGO subsystems at full mechanical scale. Credit: Bryce Vickmark

“Don’t do it; it’s maverick science.” That’s how Nergis Mavalvala’s fellow graduate students at MIT in the 1990s reacted to her interest in trying to observe gravitational waves. She ignored their advice and became an early participant in the Laser Interferometer Gravitational-Wave Observatory (LIGO), an international project started by scientists at MIT and Caltech. Her choice, of course, panned out: In 2016 the experiment announced its first detection, ripples of spacetime set off by two distant, colliding black holes. “I’ve made forays into other areas,” she says, “but instrumentation for gravitational-wave detection has remained my core passion.”

Mavalvala was a postdoc at Caltech before joining the MIT physics faculty in 2002. For the past decade or so, she says, her main scientific focus has been macroscopic quantum mechanics—how quantum mechanics can manifest on large scales. In 2010 she won a MacArthur “genius grant” Fellowship, and in 2014 the professional society Out to Innovate named her LGBTQ scientist of the year.

In 2020 Mavalvala became MIT’s dean of sciences. She is the first woman and first openly queer person to hold the position.

PT: Tell us about your path to gravitational waves.

MAVALVALA: In Pakistan, where I grew up, I was on the science and math track starting in middle school. In high school I had a really excellent physics teacher, so when I went to college I knew I would be a physics major. I majored in physics and astronomy. As an undergraduate at Wellesley College, I worked mostly on condensed-matter and solid-state physics research.

In graduate school at MIT, I met Rai Weiss and he told me about LIGO. [Rainer Weiss, now an emeritus professor at MIT, invented the detection technique underpinning LIGO. He is a 2017 Nobel laureate.] The idea of measuring displacements that are a thousand times smaller than a single proton seemed completely insane to me. For two or three days I thought about it and about the reward of being successful, how amazing that would be. I jumped in.

PT: What has been your role in LIGO?

MAVALVALA: My role has evolved over the nearly three decades I’ve been a part of LIGO. As a graduate student I was involved in developing technologies for the LIGO instruments, almost always on the optics and optical sensing side. As a postdoc and new faculty member, I spent cumulatively years at the LIGO observatories building the 4-kilometer-long instruments and making them work.

Shortly after I started my faculty position, I began a new chapter. It became apparent that Advanced LIGO, the first big upgrade, would be limited in its sensitivity by quantum fluctuations. Quantum-limited precision has preoccupied me ever since. When does quantum mechanics get in the way of making precise measurements—which it does because of the Heisenberg uncertainty principle? What can you do to get around that?

I tell potential students that our group asks, “What will LIGO need in five years?” And we invent it in our labs today so it’s ready for the big instruments.

PT: In the many years before the signal was detected, did you doubt your choice to work on gravitational waves, especially given your friends’ skepticism?

MAVALVALA: I loved the scientific puzzles we were solving and the technologies we were inventing, and I really loved the people I worked with. I also had a lot of confidence that the instruments we were building would eventually work at the sensitivity we had designed them for. My doubts were whether that sensitivity would be good enough to see a signal, because we had a lot of uncertainty about how strong the astrophysical signals would be.

PT: Where were you when the first LIGO detection was made?

MAVALVALA: I called one of my MIT LIGO colleagues, Matt Evans, early in the morning about an exam we were administering together that day for a quantum mechanics class. He was, like, “Have you seen the trigger?” We all got alerts via email, so I had seen it. I thought it must have been a blind injection; we validate our data analysis techniques by putting fake signals secretly into the data stream and then seeing if the analysis pipelines will pick up those fake signals. But Matt said it looked more interesting than that. Matt knew the instrument and data stream well, so I took another look and saw that it was a big signal. But could it be real?

Like everyone else I know who worked closely with the instrument, my first reaction was “We have to figure this signal out. This must be some kind of artifact or something we’ve done, not nature sending a message to us.” It took several weeks of very careful checking and double-checking before we were ready to say, “Wow, this is likely to be real.”

PT: Describe your work on quantum mechanics on macroscopic scales.

MAVALVALA: LIGO’s mirrors are very macroscopic—they are 40-kilogram objects. Quantum fluctuations of the electromagnetic field can kick the positions of these mirrors. And because of the sensitivity of the instrument, we can see that motion.

Separate from making better gravitational-wave detectors, I’ve been thinking a lot about fundamental quantum mechanics. At what size scale, if any, does quantum mechanics break down? Is a mirror on the scale of tens of kilograms a quantum mechanical object? Can you prepare it in a quantum state? Can you watch it decohere? Those are the kinds of questions we can start to ask experimentally.

PT: Do you have answers?

MAVALVALA: We are getting closer and closer to being able to put macroscopic objects in interesting quantum states. The first thing you would want to do is to get to a quantum ground state, and then see if you can put it in a squeezed state or some other interesting quantum state. We are able to optically cool and trap the LIGO mirrors down to seven quanta of energy—so not quite a quantum ground state. As with most really difficult things, you march your way to the ultimate goal—in this case by removing as many classical noise sources as we can, to reveal quantum fluctuations.

PT: How do you know it’s seven quanta?

MAVALVALA: We continuously measure the motion due to both quantum and classical disturbances on each LIGO mirror, and then apply an equal and opposite force with electromagnets attached to the back of each mirror. Our efforts to reduce forces on the mirrors leave them with so little energy that they move no more than 10–20 meters, less than one ten-thousandth the size of a proton. We then equate the object’s remaining energy with temperature and find that the measured degree of freedom is sitting at 77 nanokelvins, very close to its ground state, which we predict to be 10 nanokelvins.

LIGO mirror.
A LIGO technician in Livingston, Louisiana, inspects the optics that enable the observatory to detect subtle ripples in spacetime. Nergis Mavalvala and colleagues have cooled LIGO’s 40 kg mirrors to nearly their quantum ground state. Credit: Caltech/MIT/LIGO Lab (Matt Heintze)

PT: Does it take a certain personality to be able to work at the extreme precision required by LIGO?

MAVALVALA: Precision does require a special mindset. Among my colleagues, there is a lot of shared purpose, which is true in any successful organization. There is also a shared sensibility—a particular attention to detail and a certain appreciation of doing things that have never been done before and of pushing the capabilities of instrumentation. For me, that is one of the joys of the work.

I love the work, but it’s also a curse. When I do simple household repairs, I can’t believe how imprecise construction is. I think at such precise scales, and here is an entire house that was put up in a few weeks. My partner just laughs.

PT: What did winning the MacArthur grant mean for you? How did it change your life?

MAVALVALA: In some ways, the next day was very much the same as the day before, and in other ways my life has never been the same since. I think the fellowship was recognizing the funny cross-disciplinary mixture of things I was doing with gravitational-wave detection and astrophysics on the one hand, and quantum physics on very macroscopic scales on the other. It gave a certain legitimacy, that it was not a crazy cocktail of science but, rather, meaningful questions to ask.

The fellowship financially enabled my lab to do things we weren’t able to do before. And reputationally, I was able to attract amazing students and colleagues to work with me who may have not otherwise. I have also really enjoyed meeting other MacArthur fellows, especially nonscientists. I get to meet brilliant scientists all the time, but to really understand the work of people who are doing completely different things on that high level of achievement is pretty amazing.

PT: What about your being recognized as LGBTQ scientist of the year in 2014?

MAVALVALA: It was really nice to receive that award—not because it’s an award, but because I got to be among a group of scientists who identify as LGBTQ or allied. That’s relatively new in the sciences.

Science has had to play a lot of catch-up on creating a community for LGBTQ scientists. The recognition and community space are growing now, but 10 years ago there was little, and 20 years ago they didn’t exist. About 25 years ago I went with a friend to the Modern Language Association conference—the largest annual academic literature conference in the US. She invited me to go with her to the LGBTQ caucus. I thought it would be a small room with six people huddled in it. We walked into a reception with probably 200 people. At that time, you would not have seen that in science. We have come a long way.

PT: What is your experience of being an out, queer person in science?

MAVALVALA: I’ve had an extremely easy road with my queer identity, in terms of not having faced any hardship that I know of from it. People have always been accepting and friendly. But that’s not the case for most people, I know. It’s nice to know that there are more people like you, and to be a part of a community.

PT: What attracted you to the role of dean of sciences?

MAVALVALA: The first few years after we announced our big discovery with LIGO were crazy busy for me and members of the LIGO community. We were disseminating our results, going out and explaining to the world what we had seen and why it was important. The discoveries just kept coming. It was a very heady and busy time.

I wanted every person who has ever done science to have a taste of the joy of a big discovery. So when the opportunity came up to be dean, I felt like it was time for me to give back, to enable the science of others, just as people had done for me.

As dean of the school of science, I have to learn, at a relatively superficial but very broad level, all kinds of science: geoscience, neuroscience, biology, chemistry, math, and physics. And I just love that.

PT: What are your priorities as dean?

MAVALVALA: I was entrusted with being dean of one of the best schools of science in the world. So my zeroth-order priority is to maintain its excellence at every level. Don’t break it. But I do have some additional priorities: I think there are opportunities for us to be more cross-disciplinary than traditional university departments tend to be—in particular, in solving really big problems like climate change, health, and understanding consciousness, for example. As someone with oversight over multiple departments, I have the opportunity to forge more of those types of partnerships.

Another problem that we have not solved in academia is how to have every participant in our enterprise thrive and how to be diverse and inclusive. That is something I really feel I need to tackle.

PT: Have you been able to make progress in those areas?

MAVALVALA: I like to think so, but these are hard problems, and progress often comes as one step forward, two steps back, three steps forward, one step back. In the two years since I became dean, we have started a number of initiatives, but it’s still too early to see how well they are working.

PT: Anything else you’d like to add?

MAVALVALA: One other thing that I worry about and pay attention to is our social and ethical responsibilities regarding the things we invent in our labs. What are their end uses? What are their impacts on society? As a community of practitioners, whether we are physicists or other types of scientists, we have not dealt at all well with the impacts of our inventions. I would like to see this topic deeply embedded in the core of what we do. It should be part of everything we teach and every research idea we come up with. It needs to become a part of our practice.

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