Remembering Fredric Raichlen

1932 – 2014

Fredric ("Fred") Raichlen, professor emeritus of civil and mechanical engineering in Caltech's Division of Engineering and Applied Science, passed away on December 13, 2014. He was 82 years old. Raichlen was an expert in coastal engineering whose pioneering studies of tsunami mechanics have led to standards for designing tsunami-resistant structures that have saved lives around the world.

Ordinary waves are wind-driven and propagate at and just below the ocean's surface. A tsunami, however, is driven by a displacement in the earth's crust, such as an underwater earthquake or a volcanic eruption. The entire depth of the water column is set in motion from seafloor to surface. In the open ocean, the waves are hardly noticeable—the peaks are a few feet high at most, and the interval between successive waves can be several hours. But as the tsunami approaches land, the transition to shallow water concentrates the wave's energy. This rising wall of water, focused by local topography, can flood many miles inland.

That much was known when Raichlen entered the field, says his graduate student Costas Synolakis (BS '78, MS '79, PhD '86), now a professor of civil and environmental engineering at USC and the director of USC's Tsunami Research Center. But, as Synolakis says, "There were several theories and hypotheses, but there was no laboratory validation of any of them. Further, there were very few field observations. Scientists did not even know what a tsunami looked like."

This was at least partly because funding for tsunami research was hard to come by. Tsunamis were seen as a threat to other shorelines, not American ones. "Tsunamis were not trendy," Synolakis says, "and their study was considered humdrum. For almost a decade, Fred was the only professor in the U.S. working on tsunami hydrodynamics. But the students he trained, trained others. And by the time it was realized how important tsunamis are, there were knowledgeable scientists who could rise to the challenge."

Upon arriving at Caltech in 1962, Raichlen built a set of wave tanks to analyze how tsunamis originate, how they propagate through the open ocean, and what happens when they run up on shore. The data from these experiments enabled him to develop a comprehensive, three-dimensional computer model of tsunami behavior. The first part of the model described the waves' motions through the deep sea, while the second part of the model described the waves' behavior within the harbor. The two models were fused at the harbor's entrance, with the connecting region modifying the incoming tsunami's waves as they entered the harbor.

"The work he supervised remains the world standard," Synolakis says. "Nobody else before or since has done laboratory experiments of such precision and quality. Fred believed that answers could only be mined in the laboratory and that the only numerical models that could be trusted were the ones that had been benchmarked with laboratory experiments."

Previous models had represented harbors as simple geometric shapes. This model, however, re-created the harbor's interior in great detail, rendering its basins, jetties, islands, and channels as collections of line segments. The waves' reflections off of each line segment were easy to calculate when each segment was handled individually, and the tsunami's actual behavior was derived by superimposing all the reflected waves on the incoming ones to map out where they would reinforce one another and where they would damp each other out. This approach reduced the computation to a straightforward exercise in matrix algebra that could be solved on Caltech's IBM 360/75 mainframe computer—the fastest, most sophisticated machine of its day.

In 1965, Raichlen built a 31-by-15-foot wave tank instrumented to measure wave heights and water velocities anywhere within its walls. Graduate student Jiin-Jen Lee (PhD '70), also now a professor of civil and environmental engineering at the University of Southern California and the director of USC's Foundation for Cross-Connection Control and Hydraulic Research, used the tank to verify the model's predictions of wave behavior in idealized circular and rectangular harbors. He then built a scale model of the east and west basins of the port of Long Beach, California, out of 15 sheets of quarter-inch-thick Lucite. The waves created by Lee's physical model in the wave tank were well described by the mathematical model in the computer. Says Lee, "Fred wanted a theory and the numerical analysis to go with it, but he also wanted them verified against a physical model. A lot of people would just say, 'OK, I did this, and now I'll move on.' Fred was very careful to make sure that the theory could actually be checked out."

Raichlen continued to refine and expand the model. A third section was added to reproduce the different types of seabed motions that could give a wave its initial impetus. Other experiments considered a tsunami's interactions with objects floating in the harbor, such as ships and mooring platforms, or measured how fast different regions within a wave moved as the wave broke, which allowed the force of the wave's impact to be calculated.

Raichlen's model also provided the first mathematically sound explanation of how seiches, also known as "harbor waves," are created. Seiches can persist for days and are extremely damaging due to their height. They occur because every harbor has a set of resonant frequencies. Any waves of those frequencies will reverberate, amplifying themselves. Typical tsunamis have a frequency of one wave every several hours. Raichlen's model showed that many harbors also have a fundamental resonant frequency of one wave every several hours—an unfortunate frequency match that enables such a harbor to amplify a tsunami into a seiche. The model also resolved a long-standing paradox: Harbors with narrow mouths usually offer the best shelter, but those same harbors suffer the worst seiches. The model showed that as the harbor's mouth got narrower, the wave energy trapped within the harbor had less and less chance of escaping. The only way to dissipate the energy was by friction as the water sloshed back and forth.

Raichlen's commitment to his work was matched by his commitment to his students. Lee's thesis was published in the Journal of Fluid Mechanics, an unusual periodical for a civil engineer and one read by a much wider community. Says Lee, "Normally the professor and the student are coauthors, but Fred took his name out. He said, 'This is very important for your career. You should publish it as the sole author.' At first I thought that meant maybe the paper was not so good, and he didn't want his name on it. But he wanted that study to be identified with me, so he gave me all the credit. I was really moved, because it was a pretty important study. We could have published a hundred papers, each with a different-shaped harbor."

Raichlen was a hands-on adviser, spending time with each of his students every day, says Synolakis. "I will forever treasure how he trained me in the laboratory. I was a complete novice, and for several months, he stayed with me, making sure that I didn't run into trouble. He was always eager to explain what we were seeing. His attention to detail was legendary, and he could see things that nobody else could or can." 

Raichlen earned his bachelor's degree in engineering from the Johns Hopkins University in 1953 and his master's and doctoral degrees at MIT in 1955 and 1962.  He also served in the Air Force as an environmental health officer from 1956 to 1959. He came to Caltech as an assistant professor of civil engineering in 1962; he was promoted to associate professor in 1967 and to professor in 1972. In 1969, he became one of the founding faculty members of Caltech's doctoral program in environmental engineering science. He was appointed professor of civil and mechanical engineering in 1997 and professor emeritus in 2001.

Raichlen was inducted into the National Academy of Engineering in 1993, and in 1994 he received the John G. Moffatt–Frank E. Nichol Harbor and Coastal Engineering Award from the American Society of Civil Engineers (ASCE). In 2003, he was given the ASCE's International Coastal Engineering Award, the most prestigious honor in the international coastal engineering community.

In his retirement, Raichlen devoted his time to writing a book, Waves (MIT Press Essential Knowledge series, 2012). He also became an avid and prolific watercolor painter.

Raichlen is survived by his wife, Judy; his sons, Robert and David; their wives, Amy and Sarah (respectively); his sister, Linda Millison; his brother, Sonny; and two grandchildren. 

Writer: 
Douglas Smith
Frontpage Title: 
Remembering Fredric Raichlen
Listing Title: 
Remembering Fredric Raichlen
Writer: 
Exclude from News Hub: 
No
Short Title: 
Remembering Fredric Raichlen
News Type: 
In Our Community

Size Matters: The Importance of Building Small Things

Watson Lecture Preview

Strong materials, such as concrete, are usually heavy, and lightweight materials, such as rubber (for latex gloves) and paper, are usually weak and susceptible to tearing and damage. Julia R. Greer, professor of materials science and mechanics in Caltech's Division of Engineering and Applied Science, is helping to break that linkage. In Caltech's Beckman Auditorium at 8 p.m. on Wednesday, January 21, Greer will explain how we can give ordinary materials superpowers. Admission is free.

 

Q: What do you do?

A: I'm a materials scientist, and I work with materials whose dimensions are at the nanoscale. A nanometer is one-billionth of a meter, or about one-hundred-thousandth the diameter of a hair. At those dimensions, ordinary materials such as metals, ceramics, and glasses take on properties quite unlike their bulk-scale counterparts. Many materials become 10 or more times stronger. Some become damage-tolerant. Glass shatters very easily in our world, for example, but at the nanoscale, some glasses become deformable and less breakable. We're trying to harness these so-called size effects to create "meta-materials" that display these properties at scales we can see.

We can fabricate essentially any structure we like with the help of a special instrument that is like a tabletop microprinter, but uses laser pulses to "write" a three-dimensional structure into a tiny droplet of a polymer. The laser "sets" the polymer into our three-dimensional design, creating a minuscule plastic scaffold. We rinse away the unset polymer and put our scaffold in another machine that essentially wraps it in a very thin, nanometers-thick ribbon of the stuff we're actually interested in—a metal, a semiconductor, or a biocompatible material. Then we get rid of the plastic, leaving just the interwoven hollow tubular structure. The final structure is hollow, and it weighs nothing. It's 99.9 percent air.

We can even make structures nested within other structures. We recently started making hierarchical nanotrusses—trusses built from smaller trusses, like a fractal.

 

Q: How big can you make these things, and where might that lead us?

A: Right now, most of them are about 100 by 100 by 100 microns cubed. A micron is a millionth of a meter, so that is very small. And the unit cells, the individual building blocks, are very, very small—a few microns each. I recently asked my graduate students to create a demo big enough to be visible, so I could show it at seminars. They wrote me an object about 6 millimeters by 6 millimeters by about 100 microns tall. It took them about a week just to write the polymer, never mind the ribbon deposition and all the other steps.

The demo piece looks like a little white square from the top, until you hold it up to the light. Then a rainbow of colors play across its surface, and it looks like a fine opal. That's because the nanolattices and the opals are both photonic crystals, which means that their unit cells are the right size to interact with light. Synthetic three-dimensional photonic crystals are relatively hard to make, but they could be extremely useful as high-speed switches for fiber-optic networks.

Our goal is to figure out a way to mass produce nanostructures that are big enough to see. The possibilities are endless. You could make a soft contact lens that can't be torn, for example. Or a very lightweight, very safe biocompatible material that could go into someone's body as a scaffold on which to grow cells. Or you could use semiconductors to build 3-D logic circuits. We're working with Assistant Professor of Applied Physics and Materials Science Andrei Faraon [BS '04] to try to figure out how to simultaneously write a whole bunch of things that are all 1 centimeter by 1 centimeter.

 

Q: How did you get into this line of work? What got you started?

A: When I first got to Caltech, I was working on metallic nanopillars. That was my bread and butter. Nanopillars are about 50 nanometers to 1 micron in diameter, and about three times taller than their width. They were what we used to demonstrate, for example, that smaller becomes stronger—the pillars were stronger than the bulk metal by an order of magnitude, which is nothing to laugh at.

Nanopillars are awesome, but you can't build anything out of them. And so I always wondered if I could use something like them as nano-LEGOs and construct larger objects, like a nano-Eiffel Tower. The question I asked myself was if each individual component had that very, very high strength, would the whole structure be incredibly strong? That was always in the back of my mind. Then I met some people at DARPA (Defense Advanced Research Projects Agency) at HRL (formerly Hughes Research Laboratories) who were interested in some similar questions, specifically about using architecture in material design. My HRL colleagues were making microscale structures called micro-trusses, so we started a very successful DARPA-funded collaboration to make even smaller trusses with unit cells in the micron range. These structures were still far too big for my purposes, but they brought this work closer to reality.  

 

Named for the late Caltech professor Earnest C. Watson, who founded the series in 1922, the Watson Lectures present Caltech and JPL researchers describing their work to the public. Many past Watson Lectures are available online at Caltech's iTunes U site.

Writer: 
Douglas Smith
Writer: 
Exclude from News Hub: 
No
Short Title: 
Size Matters
News Type: 
Research News
Saturday, January 24, 2015
Center for Student Services 360 (Workshop Space) – Center for Student Services

The personal side of science

Wednesday, February 4, 2015
Center for Student Services 360 (Workshop Space) – Center for Student Services

Meet the Outreach Guys: James & Julius

Ravichandran Receives Award for Solid Mechanics

Guruswami (Ravi) Ravichandran, the John E. Goode Jr. Professor of aerospace and professor of mechanical engineering, has received the Warner T. Koiter Medal from the American Society of Mechanical Engineers (ASME).

The award, established in 1996, is given annually to individuals who make distinguished contributions to the field of solid mechanics.

Ravichandran, who is also the director of the Graduate Aerospace Laboratories of the California Institute of Technology (GALCIT), was noted for his "outstanding scientific, engineering, and mentoring contributions in the areas of ultra-high strain rate mechanics of ceramics and metals, and pioneering and innovative experiments to advance our understanding of coupled phenomena in the fields of smart materials and cellular mechanics."

"I am greatly honored to receive the Warner T. Koiter Medal from the ASME. I am pleased that my work is being recognized, but this would not be possible without the contributions of many talented students and postdoctoral scholars in my group," says Ravichandran. "I have also been very fortunate to collaborate with a number of colleagues on campus who have given me impetus to investigate interdisciplinary problems."

Ravichandran works to discover fundamental insights into the way that materials deform, are damaged, and fail. His primary aim is to develop new experimental methods to study these and other phenomena in solid mechanics.

Ravichandran received the award at the 2014 International Mechanical Engineering Congress and Exposition in Montreal, in November. There he gave his 2014 Koiter Lecture, titled "Peeling of Heterogeneous Adhesive Tapes."

Writer: 
Exclude from News Hub: 
No
News Type: 
In Our Community
Wednesday, February 18, 2015
Center for Student Services 360 (Workshop Space) – Center for Student Services

HALF TIME: A Mid-Quarter Meetup for TAs

Four Caltech Professors Elected to National Academy of Inventors

Caltech professors Frances Arnold, David Baltimore, Carver Mead, and Axel Scherer have been named fellows of the National Academy of Inventors (NAI).

Election as an NAI fellow is an honor bestowed upon academic innovators and inventors who have "demonstrated a prolific spirit of innovation in creating or facilitating outstanding inventions and innovations that have made a tangible impact on quality of life, economic development, and the welfare of society." Fellows are named inventors on U.S. patents and were each nominated by their peers for their contributions to innovation.

According to its website, the NAI "was founded in 2010 to recognize and encourage inventors with patents issued from the U.S. Patent and Trademark Office, enhance the visibility of academic technology and innovation, encourage the disclosure of intellectual property, educate and mentor innovative students, and translate the inventions of its members to benefit society."

Frances Arnold is the Dick and Barbara Dickinson Professor of Chemical Engineering, Bioengineering and Biochemistry, and director of the Donna and Benjamin M. Rosen Bioengineering Center at Caltech. Her group has pioneered methods of "directed evolution" to engineer new proteins in the lab. The method is now widely used to create catalysts for use in industrial processes, including the production of fuels and chemicals from renewable resources. The Arnold group also uses the results of laboratory evolution experiments to elucidate principles of biological design. Arnold is a coinventor on more than 40 U.S. patents. She was inducted into the National Inventors Hall of Fame in 2014 and received the National Medal of Technology and Innovation in 2013.

David Baltimore is the Robert Andrews Millikan Professor of Biology, and President Emeritus of Caltech. His research group focuses on two major areas: investigation of the development and functioning of the mammalian immune system, and translational studies of the viral transfer of genes into immune cells to increase their ability to fight disease and resist cancer. He was awarded the Nobel Prize in Physiology or Medicine in 1975.

Carver Mead (BS '56, MS '57, PhD '60) is the Gordon and Betty Moore Professor of Engineering and Applied Science, Emeritus, in computation and neural systems. Mead has significantly advanced the technology of integrated circuits by developing a method called very-large-scale integration (VSLI) that allows engineers to combine thousands of transistors onto a single microchip, thus exponentially expanding computer processing power. He received the National Medal of Technology and Innovation in 2002.

Axel Scherer is the Bernard Neches Professor of Electrical Engineering, Medical Engineering, Applied Physics and Physics, and the director of the Caltech Global Health Initiative. Holding more than 100 patents in the area of nanofabrication and device design, Scherer has most recently developed ways to integrate optics, electronics, and fluidics into sensor systems. Much of his work is currently focused on systems for medical diagnosis and health monitoring through molecular pathology and wireless implants. Over the past decades, technology from his group has been commercialized through several start-up ventures in telecommunications and health care devices.

Arnold, Baltimore, Mead, and Scherer will join Vice Provost Morteza Gharib, the Hans W. Liepmann Professor of Aeronautics and Bioinspired Engineering, and Robert H. Grubbs, the Victor and Elizabeth Atkins Professor of Chemistry, as Caltech's Fellows of the NAI. They will be inducted during the fourth annual conference of the National Academy of Inventors, which will be held at Caltech on March 20, 2015.

Writer: 
Exclude from News Hub: 
No
News Type: 
In Our Community

Fred Raichlen

1932–2014

Fredric ("Fred") Raichlen, professor emeritus of civil and mechanical engineering at Caltech, passed away on December 13, 2014. He was 82 years old. Raichlen was an expert on the mechanics of tsunamis, the waves created by underwater earthquakes, volcanic eruptions, and other geologic events.

Most waves propagate through the water at and just below the surface. A tsunami is fundamentally different. Because it is driven by a movement in the earth's crust, the wave extends from the seafloor all the way up to the surface. As the tsunami approaches land, the transition from deep to shallow water concentrates the wave's energy. The local topography off- and onshore focuses the onrushing wall of water, and utter devastation can follow. (The tsunami caused by the 2011 Tohoku earthquake reached six miles inland in some places and killed more than 18,000 people.)

Raichlen's wave-tank experiments enabled him to develop three-dimensional computer models of how tsunamis originate, propagate through the open ocean, and eventually run up on land. He simulated the run-up in a tank 31 feet long by 15 feet wide that was big enough to hold a scale model of an entire harbor. These experiments allowed him to design features such as breakwaters to protect a specific port or to determine where not to site vulnerable structures such as railroad tracks and oil tanks. In other experiments he determined how fast different regions within a wave move as the wave breaks, which in turn allowed him to calculate the force of the wave's impact. He also investigated the effects of the waves on floating structures such as ships moored in the harbor.

Raichlen earned his bachelor's degree in engineering from the Johns Hopkins University in 1953, and his master's and doctoral degrees at MIT in 1955 and 1962. He came to Caltech as an assistant professor of civil engineering in 1962, and he was promoted to associate professor in 1967 and to professor in 1972. In 1969, he became one of the founding faculty members of Caltech's doctoral program in environmental engineering science. He was appointed professor of civil and mechanical engineering in 1997 and professor emeritus in 2001.

Raichlen was a member of the National Academy of Engineering, and in 1994 he received the American Society of Civil Engineers' John G. Moffatt–Frank E. Nichol Harbor and Coastal Engineering Award.

The funeral will be Thursday, December 18th at 11:30 a.m. at Mt. Sinai Memorial Park, 5950 Forest Lawn Drive, Los Angeles.

A full obituary will be published at a later date.

Writer: 
dsmith
Writer: 
Exclude from News Hub: 
No
News Type: 
In Our Community

Controlling Light on a Chip at the Single-Photon Level

Watson Lecture Preview

Integrating optics and electronics into systems such as fiber-optic data links has revolutionized how we transmit information. A second revolution awaits as researchers seek to develop chips in which individual atoms control the movement of light within the chip through optical "wires," and photons could replace electrons as the vehicle for performing computations. Andrei Faraon (BS '04), an assistant professor of applied physics and materials science in the Division of Engineering and Applied Science, presents a preview of this revolution at 8 p.m. on Wednesday, December 17, in Caltech's Beckman Auditorium. Admission is free.

 

Q: What do you do?

A: My field is nanophotonics, which means that I build ultrasmall devices to control light. Electronic devices use silicon chips to control the flow of electrical charge and to store it. We're trying to do the same thing with light, using single atoms or small ensembles of atoms that act like the transistors in electronic circuits. We're building devices out of complex oxides that are similar to glass, or to quartz, but contain atoms called lanthanides that have very interesting optical properties. Lanthanide atoms can absorb light and then release it on demand at some later time. So we're making a memory device. We want to take a single photon, put it in this device, and then push a button and release that photon back into a larger optical circuit.

These devices look like the world's smallest Toblerone bars, except that each tiny triangle is attached to its neighbors at the tip instead of the base. Each bar is about ten microns long, which is about the diameter of a red blood cell, and we make them using techniques similar to those used to make computer chips. The only difference is that we're not using silicon, but these complex oxides containing lanthanide atoms.

In order to use these devices, we would have them connected to one another by on-chip optical waveguides, or to a larger system by optical fibers. The signal would come in through the fiber, get stored in our Toblerone bar for a while, and then be released back into the fiber at the appropriate time. We dream of someday having billions of components on the same chip, but even one bit of optical memory can be useful.

 

Q: What would you use a one-bit memory for?

A: It can be used in systems that transmit information with absolute security by what's called quantum communication. You can create an absolutely secure cryptographic key by sending a sequence of single photons, one at a time. Then you use the key to encrypt your data, which you can now send openly over the Internet. The systems that generate these keys over long distances are based on you sending a series of single photons from point A to point C, and a recipient sends another series from point B to point C. At point C you perform an operation on the photons, you combine them in some way, and that is used to establish the key.

However, optical fibers are not 100 percent efficient, especially over long distances. When you transmit photons through hundreds of kilometers of cable, some of them are going to get absorbed by the fiber. This isn't a big problem when each bit of information is encoded in a big pulse of light, but quantum communication depends on being able to interfere two paired single photons with each other. Many times when the photon from point A arrives at point C, you will have to store it until the photon from point B comes in. It might take a few tries before the second photon arrives, and until then the other one just waits for it.

 

Q: How did you get into this line of work?

A: When I was an undergraduate here, I really liked quantum physics. But I also had a passion for doing things that have some applications, so I went into applied physics for my PhD at Stanford. Transmitting information via cryptographic keys is one of the applications of quantum physics, so I got into this field for my PhD, and continued it during my postdoc at HP Laboratories, and now as a faculty member here.

 

Q: Bonus question: What's it like coming back as a professor after having been here as a student?

A: It feels great. Coming back to Caltech is a privilege. As a faculty member you have the satisfaction of working with all these extremely smart kids. And my wife [Assistant Professor of Biology Viviana Gradinaru (BS '05)] and I go to many undergraduate events where we connect with the students, so it feels good.

 

Named for the late Caltech professor Earnest C. Watson, who founded the series in 1922, the Watson Lectures present Caltech and JPL researchers describing their work to the public. Many past Watson Lectures are available online at Caltech's iTunes U site.

 

Writer: 
Douglas Smith
Frontpage Title: 
Controlling Light at the Single-Photon Level
Writer: 
Exclude from News Hub: 
No
Short Title: 
This Wednesday: Controlling Light at the Single-Photon Level
News Type: 
In Our Community

Quantum Code-Cracking: An Interview with Thomas Vidick

Quantum computers, looked to as the next generation of computing technology, are expected to one day vastly outperform conventional computers. Using the laws of quantum mechanics—the physics that governs the behavior of matter and light at the atomic and subatomic scales—these computers will allow us to move and analyze enormous amounts of information with unprecedented speed. Although engineers have yet to actually build such a machine, Assistant Professor of Computing and Mathematical Sciences Thomas Vidick is figuring out how some of the principles of quantum computing can be applied right now, using today's technology.

Originally from Belgium, Vidick received his BS from École Normale Supérieure in Paris in 2007 and his master's degree from Université Paris Diderot, also in 2007. He earned his doctorate from UC Berkeley in 2011. Vidick joined the Division of Engineering and Applied Science at Caltech in June from MIT, where he was a postdoctoral associate.

This fall, he spoke with us about quantum methods for encrypting information, what he's looking forward to at Caltech, and his ongoing search for the best croissants in Los Angeles.

 

What are your research interests?

My area is quantum computing, so it's the computer science of quantum physics. Classical computers—like the computer on my desk—work based on the laws of classical mechanics. They just manipulate bits and do various operations. However, in the 1970s people started to wonder what kinds of computational processes could be realized using quantum-mechanical systems. They ended up discovering algorithms that in some cases can be more efficient, or that can implement certain tasks that were not possible with classical computers.

In my research, I look at two things. One, what are the kinds of procedures that you can implement more efficiently using quantum computers? And, two, what kinds of cryptographic systems—ways to encrypt information securely—can you come up with using quantum systems that could be more secure than classical systems? It's all about this exploration of what quantum systems allow us to do that classical systems didn't or wouldn't.

 

Quantum computers haven't been invented yet, so how do you do this work?

That's a good question, and there are several different answers. Some of my research is very theoretical, and it's just about saying, "If we had a quantum computer, what could we do with it?" We don't have a quantum computer yet because it's very hard to manipulate and control quantum systems on a large scale. But that is just an engineering problem, so what people say is that yes it's very hard, but in 10 years, we'll get to it. And the theory is also very hard, so we might as well get started right now.

That's one answer. But the better answer is that a lot of what I do and a lot of what I'm interested in doesn't require or depend on whether we can actually build a quantum computer or not. For instance, the cryptographic aspects of quantum computing are already being implemented. There are start-ups that already sell quantum cryptographic systems on the Internet because these systems only require the manipulation of very-small-scale quantum systems.

We can also do some computations about properties of quantum-mechanical systems on a classical computer. One branch of my research has to do with how you can come up with classical algorithms for computing the properties of systems that are described by the laws of quantum mechanics. The most natural way to understand the systems would be to have a quantum computer and then use the quantum computer to simulate the evolution of the quantum-mechanical system. Since we don't have a quantum computer, we have to develop these algorithms using a classical computer and our understanding of the quantum-mechanical system.

 

Can you give a real-world example of how this work might affect the ways in which an average person uses a computer in the future?

One of the most basic ways that quantum cryptographic tasks are used is to come up with a secret key or passcode to encrypt communication. For instance, the two of us, we trust one another, but we're far away from each other. We want to come up with a secret key—just some sort of passcode that we're going to use to encrypt our communication later. I could dream up the passcode and then tell it to you over the phone, but if someone listens to the line, it's not secure. There might constantly be someone listening in on the line, so there is no passcode procedure to exchange secret keys between us, unless we meet up in person.

However, it is known that if we are able to send quantum messages, then actually we could do it. How this works is that, instead of sending you a passcode of my choice, I would send you a bunch of photons, which are quantum particles, prepared in a completely random state. There is then a whole quantum protocol in which you need to measure the photons, but the main point is that at the end, we'll each be able to extract the exact same passcode: me from the way the photons were prepared, and you from the measurement results. The code will be random, but we'll both know it.

And because of the laws of quantum mechanics, if anyone has been listening on the line—intercepting the photons—we'll be able to tell. The reason for this is that any disturbance of the photon's quantum-mechanical states can be detected from the correlations between the outcomes of the measurements and the initial state of the photons. This is called an "entropy-disturbance tradeoff"—if the eavesdropper perturbs the photons then the outcome distribution you observe is affected in a way that can be checked. This is a uniquely quantum phenomenon, and

it allows distant parties to establish a secret key or a passcode between them in a perfectly secure way.

 

How does your work address this?

This system of sending quantum messages was discovered in the '80s, and, as I said before, people are already implementing it. But there is one big drawback to quantum cryptography, and that's that you need quantum equipment to do it—and this quantum equipment tends to be really clunky. It's very hard to come up with a machine that sends photons one by one, and since single photons can be easily lost, it's also hard to make accurate measurements. Also, you need a machine that can generate single photons and a machine that can detect single photons for the message to be secure.

In practice, we don't have such machines. We have these huge clunky machines that can sort of do it, but they're never perfect. My work tries to bypass the need for these machines, with cryptographic protocols and proofs of security that are secure even if you can't make or see the quantum part of the protocol. To do this, we model the quantum equipment just as a black box. So my work has been to try to get these strong proofs of security into a model where we only really trust the interactions we can see in the classical world. It's a proof of security that holds independently of whether the quantum part of the device works in the way that we think it does.

 

How did you get into this field?

I was doing math originally. I was doing number theory as an undergrad and I liked it a lot. But then I did an internship, and I realized that I couldn't tell anyone why I was asking the questions I was asking. So I thought, "I need a break from this. Whatever I do for my life, I need to know why I'm doing it." The best alternative I could think of was computer science, because it seemed more concrete. And this was when I learned that quantum computing existed—I didn't know before. I think what's most interesting about it is that you're talking about the world—because the world is quantum mechanical. Physics describes the world.

That's what I really like, because from my point of view everything I do is still very theoretical work and I like doing theoretical work. I like the beauty of it. I like the abstractness of it. I like that you have well-posed problems and you can give well-defined answers. But I also like the fact that in the end you are talking about or trying to talk about real-world physics. So every time I think "Why am I doing this?" or "What should I do?" I try to think of how I can connect it to a real, concrete question.

 

How did you get interested in math and computer science when you were a kid?

My dad was a chemist but he worked as an engineer, and he would come home from work and would bring home different experiments with liquid nitrogen or whatever.

I guess he gave me sort of a scientific mind, but then why did I do math problems? Probably like most people good at math, I was just good at it for some reason and it was just easy. Math is so beautiful when you understand it. Throughout middle school and high school, I just enjoyed it so much. But then, as I said, eventually I stretched my limits in math a little bit.

 

What are you excited about in terms of coming to Caltech?

I really like the Computing and Mathematical Sciences department here—it's a young department and it's a small department. For me it's very unique in that there's a very strong group in quantum information—especially the physics side of quantum information, like my neighbor here, John Preskill. Caltech has a very strong group in quantum information and also has a very strong group in computer science. And so, from the point of view of my research, this is just the perfect place.

And then there are the mountains. I love the mountains—they're just beautiful. This is how I abandoned the smoky Paris cafes. I had to think about the mountains. You can't beat the view from my office, and I can go hike up there.

 

Other than hiking, do you have any hobbies or interests that are outside your research?

I also like to bike up mountains. I did that a lot when I came here, but then I fractured my collarbone while biking. It's almost better now, but I still haven't gotten back on the bike yet. Another thing that is an investment of time—and I'm really worried about that one—is croissant hunting. I really like croissants and chocolates. I'm from Belgium, and Belgium is pretty big on chocolate. I've already been to a lot of famous croissant and chocolate places in L.A., but I haven't found something that has lived up to my standards yet. I haven't done everything though, so I'm open to recommendations.

Writer: 
Exclude from News Hub: 
No
News Type: 
In Our Community

Pages

Subscribe to RSS - EAS