A Conversation with Robert J. Schoelkopf

William A. Norton Professor of Applied Physics and Physics

Robert J. Schoelkopf, professor and researcher in the Yale School of Engineering & Applied Science, is noted for his work on quantum transport, single-electron devices, and charge dynamics in nanostructures. He first came to Yale in 1995 as a postdoctoral researcher and joined the faculty in 1998, becoming a full professor in 2003. In January 2009, he was named the inaugural William A. Norton Professor of Applied Physics and Physics. Established in 2008 by Donald McCluskey ’42, ’59 M.Eng. as part of the Yale Tomorrow campaign, this chair honors William A. Norton, who is credited with establishing the first engineering program at Yale in 1852.

Professor Robert J. Schoelkopf

With Steven Girvin, Yale’s deputy provost for science and technology and the Eugene Higgins Professor of Physics, Professor Schoelkopf recently led a team of Yale scientists to a major breakthrough in quantum computing. The team engineered a superconducting communication “bus” to store and transfer information between distant quantum bits, or qubits, on a chip. This accomplishment lays important groundwork for putting quantum computers into real practice.

The physical laws that govern energy and matter at very small scales are quite strange to most people. Can you explain what a qubit is? What insight led you to develop the superconducting communication “bus?”

A qubit, or a quantum bit, is used to store information. Possessing two energy levels, it functions much like a bit in the computers we use today, storing data as zeros or ones. But unlike a traditional bit, a qubit has special properties that enable it to be in superposition, meaning it can hold the zero and one positions simultaneously. This allows for the exploration of many different possibilities at once.

Our qubit is made of an artificial atom constructed with a microscopic grain of aluminum. However, one qubit by itself is not very useful. In order for quantum computing to work, we have to be able to transfer information between distant qubits on a chip. To accomplish this we developed a quantum bus. Using photons as data carriers, we were able to send information along guide wires to a distant target qubit. Wiring elements together for communication is a key part of any computing scheme, but ours was the first demonstration on a quantum level.

What do you see as the next step in developing a practical quantum information processor? And what will future breakthroughs in your field mean for the average person?

One of our next steps is to connect more than two qubits together to create a network necessary to perform useful quantum algorithms. Our ultimate goal is to link hundreds to thousands of qubits together to build a quantum computer.

The power of quantum computing, for certain specific tasks, is fantastically large. To put this in perspective, even a modest quantum computer composed of a few thousand qubits would exceed the computational power of a classical computer the size of the entire universe. The best known example of the power of quantum computing is the problem of finding the prime factors of a very large number, exceeding 200 bits long. It would take a classical computer thousands of years to solve this problem. By contrast, in principle, a quantum computer could give us an answer in a matter of minutes. The fact that these problems can’t quickly be solved by classical computers is the basis for modern cryptography, so some of the first applications of quantum computing would be in cryptanalysis. But there are other uses too, such as database searching and simulating the behavior of quantum systems and materials, which will provide a better understanding of the subatomic world.

How close are we to making quantum computing a reality?

If you compare where we are now to the process undertaken to develop a classical computer, we are at the stage in the 1950s where physicists were playing around with semiconductors and learning how to make transistors that were very small and could be mass produced. So in essence, we are in the pre-computer phase, making the elements of a quantum computer.

Graduate students and post-docs work in your lab, and you teach a number of undergraduate- and graduate-level classes. What do you enjoy most about teaching and working with students?

I enjoy the classroom experience. Yale students are enthusiastic and bright and eager to learn. Hands-on demonstrations provide an opportunity to explore whether or not objects are obeying mathematical models. It’s rewarding and exciting to encourage students to think about these types of questions. I also enjoy the one-on-one process of mentoring and working individually with graduate students and post-doctoral fellows as they develop their scientific knowledge and advance in their own research careers.

Change is all around us at Yale today. As you look ahead to tomorrow, what are you most enthusiastic about?

I am enthusiastic about the many promising lines of research on campus, and not just in my field but across the disciplines. We are conducting more and more interdisciplinary work at Yale that traverses the traditional boundaries between, for example, theorists and experimentalists, or physical scientists and biological scientists. Researchers are coming together across disciplines to collaborate on solving the emerging problems of our time. As a result of this work and the depth of the expertise here, the University continues to invest in shared resources for cutting-edge research, including state-of-the-art microscopy equipment and clean rooms. These tools are essential for the kind of work we do, and we have access to them because of the many high level scientists and students at Yale that make can excellent use of them. In all, there are immense possibilities for a transformative discovery happening tomorrow, and that is what is exciting about being at Yale today.

About Robert J. Schoelkopf

Professor Schoelkopf is a graduate of Princeton University and earned his Ph.D. at the California Institute of Technology. Before coming to Yale, he was an electrical/cryogenic engineer in the Laboratory for High-Energy Astrophysics at NASA’s Goddard Space Flight Center, where he developed low-temperature radiation detectors and cryogenic instrumentation for future space missions. He has been an invited lecturer at universities and professional organizations around the world, and his honors include the American Physical Society’s 2009 Joseph F. Keithley Award for Advances in Measurement Science and NASA’s Technical Innovator Award. He is also a fellow of the American Association for the Advancement of Science and the American Physical Society.

(June 15, 2009)