Idea Flow - Making a Dramatic Change by Starting with the Fundamentals

IDEA FLOW Making a Dramatic Change by Starting with the Fundamentals by Sandy Irani Sandy Irani is a Professor of Computer Science at the University of California, Irvine, and a Visiting Associate in the Caltech Department of Computing and Mathematical Sciences. After making a major change in her research focus, Professor Irani spent a sabbatical year at Caltech's Institute for Quantum Information (IQI). The abstract nature of math fascinates her, and she spends her days as a computer scientist applying mathematical techniques to fundamental problems in physics. I have had a very dramatic change in my research focus in munity of researchers working on quantum computation. the last five years. I used to work on online algorithms, and The idea behind the general area of quantum computa- now I'm working more in the area of quantum information tion is that we can use matter at the quantum level to store and computation. The change came about simply because I and process information, like storing a bit of information got restless and wanted to work on something new. We're in the spin of an electron. The laws of physics are quite dif- very lucky in academia that we can decide to do something ferent at this level than they are at the macroscopic level. completely different and don't need to ask anyone's permis- In theory, at least, if this could be accomplished, we could sion. We just have to learn build computing devices the new area. It was a big change and a fairly steep learning curve to get into a new area, but it was very interesting. I had a good time learning a new topic. My previous research area was in traditional Our business in theoretical computer science is to understand mathematically the computational difficulty of problems and to classify them in terms of their complexity. that are much more powerful than conventional classical machines. We can't actually build these machines yet, but in the meantime, we are trying to answer questions like, if these machines could algorithm design, and I be built, what exactly specialized in applications to computer systems. I worked can we do with them? What is their power computation- on things like memory management, web caching, and dif- ally? What kinds of problems can they intrinsically solve? ferent ways of computing with low power, like algorithms What I am interested in is asking these kinds of for powering down laptops and, therefore, all kinds of op- questions in relation to problems in physics. Physicists timization problems as they applied to computer systems. have been using computers for decades to understand I don't really know what made me change fields; quantum systems: to simulate them over time or to com- I just wanted to learn something new, and I was repute their fundamental properties. Some of the tech- ally poking around in the dark. What 1 did know was niques have been very successful, some not so successful. that I wanted to start with the fundamentals and re- They just seem to work well in certain situations. What ally learn about the basic science before I jumped in. I wanted to do was to really understand these questions I started by taking a quantum mechanics class and actu- from the point of view of computational complexity. Our ally doing the homework. I was always curious about quan- business in theoretical computer science is to understand tum mechanics. I had never taken it in college and I knew mathematically the computational difficulty of prob- that within computer science, there was a growing com- lems and to classify them in terms of their complexity. 50 ENGenious NO.7 2010 IDEA FLOW expect, either with classical computers or even quantum computers, to be able to solve this problem. But there's a positive side to this result in that the proof involves showing that the lowest energy state of a one-dimensional quantum system can encode the answers to hard problems. So this presents the possibility of a new model for a one-dimen-sional quantum computer instead of a two-dimensional one. What I find very compelling about this new field is that by putting computer scientists and physicists to-gether, researchers are actually coming up with new ways to solve physics problems on garden-variety classical computers. These new solutions would not have been uncovered if we had not been looking at these problems through the lens of computation and information. It may be a while before we have large-scale quantum comput-ers, or maybe never, but many interesting things are coming out of the cross fertilization between physicists and computer scientists at national powerhouses such as IQI. IQI is one of the main reasons I chose to do my sabbatical at Caltech. While there is a lot of exciting research happening at the University of California, Irvine, there is no one else working in quantum information science, so I felt a bit like I was in a silo. Also, I am not free to get up and move across the country for a year because of my family. I was, therefore, lucky to have IQI within driving distance It's a hotbed of activity that has been instrumental in bringing people together and creating a center of activity. If you One of my first pivotal moments in quantum infor- look at the list of postdocs that have come through IQI, it mation came about three years ago when we discovered a basically reads like a who's who in the field. There's a whole surprising result about the inherent computational difficulty community of people working on questions that I'm inter- of a problem that physicists have been using computers to ested in, and all kinds of related questions in the general field solve in special cases. A fundamental problem in computa- of quantum information. Two other aspects that make IQI tional physics is to find the lowest energy state of a system, so successful are its physical location in the new Annenberg given the parameters. Physicists believe that this problem Building for Information Science and Technology and its is computationally difficult for two-dimensional systems, steady stream of visitors. IQI is a common destination for but easier for one-dimensional systems. This belief is based top researchers and scientists from around the country and on experience, since algorithms have been developed that the world to come and spend a few days or a few weeks at. work quite well on special one-dimensional cases. How- Even though I am no longer on sabbatical, I have ever, we still didn't know if there were a general algorithm been coming back to Caltech on a regular basis to at- that, given any one-dimensional quantum system, could tend talks and work with colleagues. I am sure that compute its ground state. We showed that one-dimen- IQI will be an important resource for me as I con-sional systems can, in principle, also be computationally tinue to work in this exciting and growing field. ONe difficult [D. Aharonov, D. Gottesman, S. Irani, J. Kempe. The Power of Quantum Systems on a Line. Communications Sandy Irani is Visiting Associate in Computer Science at Caltech on Mathematical Physics, vol. 287, no. 1, pp. 41-65, 2009.] and Professor of Computer Science at UC Irvine and hence brought some bad news into the picture. We don't Visit: http://www.iqi.caltech.edu 51