New Caltech faculty member Alireza Marandi is on the cutting edge of laser science. Marandi, assistant professor of electrical engineering in the Division of Engineering and Applied Science, explores how nonlinear photonics, a field of optics, enables a broad range of previously less-explored opportunities for using lasers and light detectors for a variety of purposes, including molecular sensing and computing. Although lasers currently are used for a number of important applications from surgery to communications, imaging, and sensing, the devices are not always available at the wavelength needed for a given application. Marandi and others are exploring ways to convert laser wavelengths to suit any given purpose, by passing the light through specially engineered devices. Such nonlinear devices can also be used in information processing. Marandi received a bachelor's degree from the University of Tehran, a master's from the University of Victoria, and a doctorate from Stanford University. Recently, he answered a few questions about his life and work.
Caltech has a great focus on science and engineering. Everyone you meet shares the same passion and drive, which fosters strong collaborations and motivates you to dig more deeply into your own field and be more effective. It has been a utopia for the type of research I am interested in.
Moreover, Caltech has played a critical role in the evolution of electrical engineering and photonics. Many of the prominent figures in the field have been at Caltech at some point in their careers as students, postdocs, or faculty members. It is extremely exciting for me to be a part of this community and contribute to its extraordinary impact.
When I was in primary school, I saw one of those sci-fi movies that had lasers in it. I don't even remember the name of the movie, but it got me interested in understanding what a laser was and how it was different from other light sources. Being a bookworm at the time, I actually went out and bought a laser textbook. Except for the first few pages, I could not understand anything in that book, but it helped me create an imaginary picture of the physics behind lasers. It was fun. Of course, everyone teased me for having a laser textbook in primary school.
Later, in high school, I got my hands on some laser diodes and built the simplest optical communication link. It was my first serious photonic experiment. When I got to college, I knew I would do electrical engineering. I had always been the type of kid that would try to build things. My parents may not agree with me on the term "build," but I "worked" with a lot of electronics in high school.
As an undergrad, I got a little off-track from photonics and found myself working a lot with artificial intelligence. I used artificial intelligence to design electromagnetic structures, which we built and tested. That got me back into learning more about electromagnetics and optics. Fast forward to after my PhD, when I ended up using photonic structures to solve some artificial intelligence problems. So, everything connects in a nonlinear way. In hindsight, one of the most appealing elements of photonics for me is that you can find a nice balance between science and engineering design and development.
Think of breath analysis. There is a correlation between the molecular composition of your exhaled breath and what exists in the blood. So, there's a lot of useful information about your health contained in your breath, but it is difficult to analyze because the concentrations are so low. To overcome that, you could analyze the spectra of exhaled breath using lasers, searching for the spectral "fingerprints," or signatures, that reveal the presence of those compounds. The problem is that those fingerprints sometimes only show up at certain wavelengths of light, for which lasers and light detectors are not easily available. Wavelength conversion in nonlinear photonics enables accessing that information using the currently available lasers and detectors.
There are two application directions that I'm particularly excited about: one of them is related to information processing and the other is related to sensing, which I just described. For information processing, nonlinear photonics can provide access to extraordinary functionalities ranging from low-power logic operations to generation and manipulation of quantum states of light,but the challenge is that it's expensive and not easy to scale at the moment. The important question is how you can bring such functionalities, either for sensing or information processing, into a scalable platform to solve real-world problems.
New Assistant Professor of Chemistry Kimberly See caught her first glimpses into the world of chemistry growing up in Colorado. She originally thought she wanted to be a botanist, but then began to realize that plants—and everything else around her—are made up of molecules, and switched her interest to chemistry.
"My chemistry kit was going outside and playing in the streams and being in nature and climbing in mountains and trees," she says in a new video profile.
After earning her bachelor's degree in chemistry from the Colorado School of Mines in 2009, she went on to UC Santa Barbara, where she received her PhD in 2014. She worked as a postdoctoral scholar at the University of Illinois at Urbana-Champaign until last year, when she joined the Caltech faculty.
See's passion for the outdoors led her to focus on energy research, and more specifically, battery chemistry. She and her students are looking into potential new electrodes and electrolytes that go beyond the traditional chemical reactions using lithium-ion batteries. For example, they are studying the chemistry of magnesium and other abundant, less-expensive resources that might one day be used in batteries for electrical vehicles or other forms of renewable energy storage. Says See, "the ultimate goal of our lab is really to develop new chemistry."
How do cells make decisions to divide, to differentiate, or to work together? For former physicist Matt Thomson, these questions drew him out of physics and into the study of computational biology. Thomson recently joined the Caltech faculty as an assistant professor of computational biology. We sat down with him to discuss his work and how he made the leap from physics into the world of the living.
It's a lot of different things. For me, it's really about building models of cells and cell behavior.
Cells have a fascinating ability to make decisions. How does a stem cell decide to become a neuron, or a muscle cell? We try to answer this in my lab by building mathematical models of the networks of proteins inside single cells, in order to understand how they allow the cell to collect information and make developmental decisions.
In this way, we examine the molecules inside the cell, but we also look at how the cells themselves all work together to do things like construct a brain. We build models of collective cell behavior. One of the really weird things about development is that there are trillions of cells moving around. There's no master plan and yet somehow everything gets to the right place. How does this distributed system construct an organized tissue that can actually function?
Inside each cell is a complex web of proteins called a regulatory network, kind of a chemical computer. They take information from outside of the cell—like signals sent from nearby cells—and change gene expression accordingly. We build models of cellular regulatory networks using dynamical theory, a branch of mathematics, in order to understand when and how cells decide what to do.
You can build models of cells by measuring the messenger RNA (mRNA) abundance of every gene in the genome of a single cell. The different abundances of mRNA molecules tell you which genes are being turned on, and how strongly.
To do this, first you take cells from a tissue and put them inside water droplets, such that each droplet gets a single cell. Then you break the cell open inside the droplet, capture the RNA inside, and sequence it.
In particular, we study in vivo mouse brain development, but we can make cellular models for different kinds of mouse tissues at different stages of development. We can basically record the history of cells going through development. Our sequencing machine allows us to profile 100,000 cells per day.
For a long time, I've been interested in life and how it works. I've especially been interested in the idea that organisms can process information and do computing.
During graduate school, I started becoming interested in life, biology, and information processing. Then it was a matter of deciding exactly where in these fields I could enter. My first project in biology was doing some theoretical work on the nanopore sequencer. Nanopore sequencing is a way to do DNA sequencing by pulling a piece of DNA through a very small hole in a piece of silica.
At the time, people needed theoretical work to understand how the DNA interacts with the hole, so that was the very first thing I did. While I was doing that, I realized, "This isn't the interesting part. The interesting thing is how cells work, how organisms work." So, I got involved with renegade physicists who were starting to do modeling of biological systems on all different scales. That happened for me when I was a master's student.
I was in Boston for a really long time—I was at Harvard for both undergrad and grad school. For my PhD, I did a big blend of theory, data analysis, and experimental work, all about decision-making, dynamical systems, and models of cellular/regulatory networks.
Then I went to UC San Francisco as a Theory Fellow. I was interested in starting to work on collective behavior—how cells interact. I also worked on self-organization of tissues and some statistical methods doing data analysis. Then I got an Early Independence Award from the National Institutes of Health that let me hire a few people, and that was great because then we could actually start collecting some data. I was there at UCSF for a total of six years, which was crazy. That's long.
Then, Caltech was doing this computational biology search. A lot of the people I worked with over the years had given me a great admiration for Caltech, and I always admired the history of really taking on very deep scientific problems, so I was excited when there was a search that appeared to be a good fit.
I have two kids, a four-year-old and an 18-month-old. We love California and do a lot of California things, like going to the beach, hiking, being in the ocean. My free time is focused around playing music, trying to learn Spanish, and exploring a lot.
Yes, science was always a hobby of mine when I was younger. I grew up in a small town about an hour from St. Louis, and as a kid I spent a lot of time outside in the woods. That's the defining experience of my childhood, and I think it had a big influence on me.
Protein complexes are intricate biomolecules, used in essentially every task carried out by cells. Rebecca Voorhees, assistant professor of biology and biological engineering and Heritage Medical Research Institute Investigator, is fascinated by how proteins are made, the cellular quality control mechanisms that destroy defective or unnecessary proteins, and how these mechanisms malfunction during diseases like cancer.
Voorhees joined the Caltech faculty this year and most recently was named a 2018 Pew-Stewart Scholar. We sat down with her to discuss the life cycle of proteins, the state-of-the-art microscopes crucial to her work, and life back in the United States after 10 years in England.
Broadly, we are trying to understand two related areas of biology: protein biogenesis—how proteins are made, how they get to the right places in the cell, how they are assembled—and what happens when these processes fail. How does the cell recognize when something has gone wrong? How does it degrade a bad protein to prevent disease?
To look at protein structure, our laboratory uses X-ray crystallography—where you shoot X-rays through a crystallized sample and observe how they scatter—and cryo-electron microscopy, or cryo-EM. Cryo-EM allows us to take detailed images of a protein at very, very cold temperatures. Caltech has actually just set up a new facility with two cryo-EM microscopes, which is really critical and exciting for my research and for others at Caltech interested in protein structure and molecular mechanisms.
We are particularly interested in membrane proteins, which make up a fairly large proportion of proteins made in the cell. Membrane proteins have large stretches of hydrophobic, or water-repellant, amino acids because they ultimately end up in the cell's membrane, which is hydrophobic as well. The challenge is, cells have to make these proteins in an environment full of water. How does the cell deal with these hydrophobic sequences? How do you get them to the right place? What happens when these processes fail?
When a membrane protein fails to make it to the membrane, it can create aggregates, or clumps, of proteins within the cell. Protein aggregates are associated with diseases like Parkinson's and Alzheimer's.
I grew up in Chicago and went to Yale for my undergraduate degree in biophysics and biochemistry. Then I was in England for 10 years, for graduate school and a postdoctoral fellowship at the Medical Research Council Laboratory of Molecular Biology. I just moved back this past summer.
I never felt like I was really British, even though I had been there for a long time. So being back in the U.S. is like coming home and I'm really excited about it. But it does take some getting used to—especially the sunshine and warm weather.
One thing I will try to bring with me from England is that we would always have tea and cake every afternoon with the lab. It was a really informal way for people to chat, sometimes about science and sometimes not. It fostered a lot of casual interactions and discussions that it's difficult to engineer in any other way. So, I'm hoping we can at least partially implement something like this in my lab.
I played intercollegiate water polo during undergrad at Yale. It got me into the habit of waking up really early, so most days I'm up at 5 a.m.
Ever since his parents bought him a chemistry kit in elementary school, Maxwell (Max) Robb has wanted to be a chemist. Now, as a new assistant professor of chemistry at Caltech, Robb possesses the grown-up equivalent of a chemistry kit—a new state-of-the-art laboratory for making materials, in particular plastics that respond to mechanical forces. Robb's research has important applications like sensing stress in plastics, where mechanically sensitive molecules could signal impending damage by changing color. But his passion lies in fundamental chemistry. "I like making new things and exploring the chemical world," he says.
Robb moved to Pasadena after a postdoctoral fellowship at the University of Illinois at Urbana-Champaign. He earned his PhD in chemistry in 2014 from the University of California, Santa Barbara, and his bachelor's degree in chemistry from the Colorado School of Mines in 2009.
We sat down with Robb to learn more about his research and why making plastics is not that different from cooking.
In my lab, we make new materials. We make small molecules as well as large molecules such as polymers, which are long chains of repeating units. You can think of a polymer as being like a spaghetti noodle. If you cook spaghetti, you end up with a tangled ball of noodles. The same is true for the materials we make in our lab—the polymers become tangled together, and this gives rise to many of their properties.
The research in my group focuses on functional polymers, or functional plastics. We're interested in tuning the structure of these materials, at the molecular level, so that when you apply a stimulus, by pulling on the material or applying a mechanical force, it causes some chemical reaction, some transformation, to take place. Such changes would provide a simple visual cue, for example, that would allow you to identify if a plastic component has been subjected to a potentially damaging stress. We are particularly interested in developing polymers that provide a visual readout of the amount of force a material has experienced.
This technology could be applied to personal protective equipment—helmets, for instance—to provide immediate information about the severity of an impact to the head. That feedback could then be used to inform medical treatment. For industrially relevant plastic components, we could identify stresses early on that would eventually cause the material to fail, so that the parts could be repaired or replaced before more significant damage occurs. We are also working on a type of "invisible ink" for polymeric materials—where mechanical force would be used to write a pattern that can be revealed later using a secondary stimulus.
Typically, we start with an idea for a new molecule or material and then we perform computational calculations to try to predict how the molecule will respond to mechanical force. From there, we go into the lab and synthesize the new materials. Sometimes we will modify existing molecules that we know behave in certain ways, and sometimes we'll develop completely new materials. However, the ability to design new mechanically responsive molecules from the ground up is still a big challenge in the field. My group is working on this by developing the fundamental framework for understanding how force is coupled to molecular reactivity.
The community aspect of Caltech is really special, coupled with the small size of the Institute. The people here are incredibly friendly, open, and supportive. People are collaborative, everyone is doing amazing science, and there are zero barriers to interacting with anyone on campus. And the students are absolutely amazing. I've been lucky to recruit an outstanding group of researchers.
I like hiking and exploring the outdoors. I love living near the mountains. I enjoy trying all the restaurants that Pasadena offers, but I also like to cook. Synthetic chemistry is a lot like cooking. I think there's a correlation between being a good synthetic chemist and being a good cook at home. I wish I had more time to be creative in the kitchen. Watching a good TV show or movie is one of my guilty pleasures.
New Caltech faculty member Claire Bucholz is a globe-trotting field geologist studying igneous rocks from the transition between the Archean and Proterozoic eons 2.5 billion years ago, which roughly coincides with a time period known as the Great Oxygenation Event (GOE), when oxygen began appearing in the earth's atmosphere. She hopes to better understand what impact this had on the earth's crust and, in turn, how that may have impacted processes deep inside the planet. A native of Irving, Texas, Bucholz completed her undergraduate studies at Yale and earned a PhD through the MIT/Woods Hole Oceanographic Institute Joint Program in Cambridge in 2016. Recently, Bucholz answered a few questions about her research and the important clues about the earth's deep past that can be found in the rock record.
I think about the composition and chemistry of igneous rocks from a field-based perspective. My studies all start with detailed field observations and then build up from there with layers of new data from microscopy, mineral and rock chemistry, isotopic analyses, geochronology, and more. Some of the big questions I am thinking about include how changes in conditions and the surface of the earth—for example, the rise of oxygen or the oxygenation of the deep oceans—may have been imprinted on the igneous rock record and how the continental crust is constructed.
My mom jokes that I always wanted to be a "rock scientist" and was filling my pockets with rocks from the time I was able to toddle about. But what really got me excited about geology was a semester abroad in Switzerland in high school. Our science curriculum was geology. We conducted labs sitting on moraines overlooking vast glaciers or observing metamorphic rocks that had originally been part of the sea floor but are now at some of the highest peaks in the Alps. It was a surreal and totally engrossing experience.
As my research is based in detailed field studies, I get to travel to some amazing places to observe and collect rocks, then take these rocks back to the lab, analyze them, and synthesize all of the data into a larger picture. This process is a really unique way to connect with a place. It makes you feel a really close connection with the earth.
I have to admit that I thought I made a terrible mistake when I first moved here. It was actually the one place I swore I would never move to. I remember driving over Cajon Pass and down into the Inland Empire in early September into the thick heat and smog. However, I've adjusted and am actually now a complete fan of Southern California. The weather, of course, is great, but the ability to get outside to the beach or to the mountains on the turn of a dime is incredible. There is a wealth of natural beauty here and such a visceral connection with geology that is unlike anything I have experienced in a big city before.
I mostly try to keep the chaos of my two kids to a reasonable level. However, I'm an avid gardener and have been loving the Los Angeles climate. My family and I also enjoy exploring the San Gabriel Mountains and the coastline during the weekend.
Not many people get to turn their childhood hobby into a career, but when Joe Parker began collecting insects at the age of 7, he simply never stopped. Parker took his childhood fascination with insects to the next level, amassing a diverse and pristine collection from the Welsh countryside surrounding his hometown of Swansea in the United Kingdom. It was only natural for him to turn this love of insects into a career, and, in 2017, Parker arrived at Caltech as an assistant professor of biology and an affiliated faculty member of the Tianqiao and Chrissy Chen Institute for Neuroscience. He now focuses on small species of beetle that have the potential to answer fundamental questions of evolution.
Nick Hutzler, a new assistant professor of physics, is returning to Caltech after 10 years of probing the fundamental laws of physics at Harvard University. He earned his undergraduate degree in mathematics from Caltech in 2007, then switched to physics, earning his PhD from Harvard in 2014 and completing a postdoctoral fellowship, also at Harvard, in 2017.
Hutzler uses tabletop experiments to study the fundamental particles and laws of nature. Unlike particle accelerator experiments, where atoms are smashed together, he uses laser beams to carefully probe atoms and molecules and look for the hidden influences of never-before-seen particles and "broken symmetries" in the laws of physics.
We sat down with Hutzler to talk about his move back to Caltech and the advantages his tabletop technique brings to particle physics.
What made you switch from mathematics to physics?
I was a math major at Caltech, but I did a lot of physics. During my freshman year I was a SURF [Summer Undergraduate Research Fellowship] student at JPL and then my sophomore year I started doing research with Brad Filippone [the Francis L. Moseley Professor of Physics]. I continued doing research with Brad until I left for Harvard. I still use math every day, but now as an experimental physicist, I also get to hit stuff in the lab with a hammer and shoot lasers!
How are you able to probe matter at the most fundamental levels with tabletop experiments?
My goal is to look for the signature of new physics interacting with regular matter—in particular, atoms and molecules. If you can perform very precise measurements of the properties of atoms or molecules, you can actually see signatures of the same types of particles found in particle accelerator experiments.
In our experiments, we take atoms or molecules and put them in an ultrahigh vacuum chamber so that there's nothing, such as background gas atoms, bumping into them. You cool them down so that you don't have to worry about thermal effects or the molecules bouncing into each other. And then you shoot a laser at the molecules to push around the electrons and nuclei and see what happens.
What kinds of signals are you looking for?
We're looking for effects that violate fundamental symmetries in the laws of physics, meaning that we're looking for something that shouldn't actually be there at all. For example, we know the universe is made out of matter and not antimatter, which means that some kind of symmetry was broken in the laws of physics—otherwise, we would have the same amounts of matter and antimatter. This is called the baryon asymmetry problem. We're looking for signatures of this same type of symmetry breaking in the atoms and molecules in an electromagnetic field, specifically by looking for energy shifts that violate the symmetry rules found in textbooks on electromagnetism and quantum physics.
Are other scientists doing these same types of experiments?
It's not a big field. There are a handful of people taking this specific approach of using atoms and molecules. There are other people at Caltech looking for these symmetry violations with similar experiments but in different particles; for example, Brad Filippone is looking in neutrons, and Ryan Patterson [professor of physics] is looking in neutrinos. Also, Frank Porter [professor of physics] and David Hitlin [professor of physics] search for symmetry violations in heavy, unstable particles called mesons.
What drew you back to Caltech?
What drew me to Caltech as an undergrad and as faculty is that it's pretty unique. It's small and overwhelmingly focused on science and engineering, and has lots of world-class research going on. There are not very many places that offer all of that and none that offer it in the way that Caltech does.
Our lab on the first floor of Downs-Lauritsen is just about completed, and we're excited to get to work. That's one of the nice things, in my opinion, about this tabletop approach to looking for new particles: you can do this all here. You don't have to go to an accelerator or a telescope. We can just do it all on the first floor of Downs-Lauritsen.
New faculty member Jim Fuller, assistant professor of theoretical astrophysics, studies vibrating cosmic spheres, such as stars with "heartbeats," and the gas giant Saturn, whose pulsations propagate through its rings. He is a theorist who uses math, physics, and numerical simulations to tackle astronomy problems, in particular those related to a planet's or star's internal structure and evolution. Fuller says he fell in love with astronomy when he was young and realized he could use his imagination.
"In astronomy, you think about things you don't encounter in your everyday life, like stars, where you really need to use your imagination because the scale is so large," he says. "But at the same time, astronomy is concrete. There is really something happening out there, and we are applying math and physics to real situations to learn more about our universe."
Fuller received his bachelor's degree from Whitman College in 2008, and his PhD in astronomy and space sciences in 2014 from Cornell University. He joined Caltech as a DuBridge Postdoctoral Fellow in 2013 and joined the Caltech faculty in 2017.
Below Fuller describes, in his own words, some of the movies he has made to illustrate how to "take the pulse" of planets and stars.
The pulsing orbs in this movie are known as "heartbeat" stars. These are binary star systems with very eccentric orbits. At closest approach, which occurs at around seven seconds into the movie, the stars come within a few stellar radii of each other. Their mutual gravitational forces distort the stars into elliptical shapes, changing their observed cross section and apparent brightness. This creates a heartbeat-like pulse in the light curve below the stars.
The brightness changes caused by these so-called tidal distortions have been detected by NASA's Kepler space telescope, leading to the discovery of hundreds of these heartbeat-star systems. Some heartbeat stars do not relax back to their original shape after their closest approach, and they continue to pulsate throughout their orbits as illustrated in this movie. These stellar oscillations cause the stars to dissipate orbital energy, which causes their orbits to circularize. You can also "hear" a heartbeat star below, where I have converted the light curve detected by Kepler into sound and sped things up by a factor of 5 million.
I'm trying to better understand the evolution of heartbeat stars' orbits through a combination of theory and observations.
Like stars, gaseous planets such as Jupiter and Saturn are continually distorted by their own minute pulsations. With Saturn, we cannot see these pulsations directly, but we have learned to use its rings as a giant seismograph. The small gravitational variations caused by pulsations of Saturn exert small torques on orbiting ring particles, generating spiral waves within the rings. These ring disturbances were detected using NASA's Cassini satellite, which later plunged into Saturn in September 2017.
This movie shows an exaggerated example of a pulsation from Saturn propagating around the equator of the planet. The pulsation causes a spiral density wave in the rings that propagates at the same rate. The motion of these spiral patterns then tells us the frequency at which Saturn pulsates, and this can be used to measure properties of the interior of Saturn. My work suggests that Saturn's interior is more complex than previously believed, with an "outer core" composed of a mix of the icy/rocky core material and the gaseous material found in the outer envelope.
Stars in a later stage of evolution, called red giants, exhibit minute pulsations caused by continual "starquakes." Like terrestrial oscillations that occur after earthquakes, starquakes can be used to measure properties of the internal structures of stars because they result from sound waves that propagate through the stellar interior and carry information back to the surface. The movie illustrates a path that a wave would take on its journey between the core and surface of a star if it was able to travel unimpeded. By studying the theory of how waves travel through stars along with some observations of the phenomenon, I helped discover something new about red giants: magnetic fields disrupt the propagation of waves near the core of the star, causing the stellar pulsations to be suppressed. This suppression phenomenon has since been observed in thousands of red giants, suggesting strong internal magnetic fields are more common than we previously believed.
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