Fall 2019 > Research Excellence

The Chase is Still On

Quantum computing is probably one of the most popular technological buzzwords these days, but how many of us actually have a clue what it is? Everyone from scientists to tech giants like IBM, Google, and Microsoft is joining the race to develop quantum computing technology and pushing the field forward. After Google launched its 72-quantum bit (qubit) quantum computer last year, IBM announced that its latest 53-qubit quantum computer would soon be rolled out for research and commercial use.

How do qubits—the basic unit of quantum information—outperform the conventional computing bits that we are familiar with? First, we must grasp that “qubits are the quantum computing version of bits, but rather than storing either a 1 or a 0, a qubit can store both, either, or neither at once, which dramatically increases the potential processing power of a computer.”1 Simply put, when qubits achieve a mixed state of “superposition,” they can make computing more efficient by storing and processing more data when solving complex problems in areas such as machine learning, optimization planning, logistics, fintech, biomedical, materials science, and many more.




Hunting the Mysterious Particle

What are qubits made of?

Majorana fermions are quantum particles that have the potential to be qubits. These particles are named after the Italian theoretical physicist Ettore MAJORANA who in 1937 predicted the existence of particles that have their own antiparticles. The uniqueness of Majorana fermions led scientists to hypothesize that they could be used to form qubits, the building blocks of a quantum computer. Since then, scientists worldwide have been searching high and low for these mysterious particles.


In the past decade, experts in the field of condensed matter physics have taken a step closer to identifying the existence of Majorana fermions. In 2012, nanoscientist Leo KOUWENHOVEN, a Professor of Physics at the Delft University of Technology in the Netherlands, and his research team created Majorana fermions on a chip, proving the existence of this particle.


However, skeptics argued that the same signal could be produced by other phenomena. One of the leading experts on high-temperature superconductivity who held such a view was Prof. Patrick A. LEE, William and Emma Rogers Professor of Physics at the Massachusetts Institute of Technology (MIT) and an IAS Senior Visiting Fellow, who argued that “other peaks in Kouwenhoven’s data point to the existence of non-Majorana states that could be mimicking the long-sought-after phenomenon. Even if Majorana fermions have surfaced, those other states could prove a problem for any possible application in quantum computing.”2



A Life-long Scientific Journey

Growing up in the 1950s, Lee was captivated by popular science which sparked his lifelong interest in mathematics and physics. “I was also greatly inspired when the first two Chinese, YANG Chen-Ning and LEE Tsung-Dao were jointly awarded the 1957 Nobel Prize in Physics,” he said. This Hong Kong-born American scholar, who perhaps at the young age had never thought that he would devote himself to the research of condensed matter theory and high temperature superconductivity, received the Oliver E. Buckley Condensed Matter Physics Prize in 1991 for “his innovative contribution to the theory of electronic properties of solids, especially for strongly interacting and disordered materials.”3

“Nature is a miracle, and there are lots of things to be discovered,” Lee commented. He took the discovery of the Quantum Hall Effect (QHE) in the 1980s as an example showing how new phenomena lead to new research directions and possibilities. He remarked, “in the past, people had to go to a special lab to study QHE. In recent years, people discovered that even in the absence of an external magnetic field, the experiment can be carried out. This is a great benefit.” As a theoretical physicist, Lee enjoys working with colleagues who are in the field of experimental physics and proposing new experiments. “I like my field, as theories and experiments are closely related and can be developed at the same time. It is the intellectual curiosity that steers us to search for new findings.”

Along with a team of experimentalists at MIT and at the University of California, Riverside, Lee published a paper titled “Superconductivity in the Surface State of Noble Metal Gold and its Fermi Level Tuning by EuS Dielectric” in Physical Review Letters this year.4 Back in 2012, Lee had already predicted that a topological superconductor that hosts Majorana fermions could be formed by the heterostructures of gold. Several years later, he and his team used gold to develop a new heterostructural material system composed of “layers of drastically dissimilar materials” to demonstrate the existence of Majorana fermions. Prof. Peng WEI, Assistant Professor of Physics and Astronomy at the University of California, Riverside, who collaborated with Lee and other scientists in this study, stated that the research was “important for future manipulation of Majorana fermions, required for better quantum computing.”5

Lee recently visited the IAS to participate in this summer’s Gordon Research Conference on “Topological and Correlated Matter: New Materials and Structures in Topological and Correlated Systems” and deliver a talk reporting the new experimental findings, with the title “Finding Majorana on an Island in a Sea of Gold”. He commented that gathering so many experts from around the world to share the latest development in the field was a wonderful experience, and that “this is my third time coming to the GRC held at the IAS. Everyone was very excited about this field, a hot topic which has been developed so rapidly. Collaborations often happen after people return to their home institutions and continue the discussion and exchange of ideas.”

Surrounding Prof. Lee at the conference were many familiar faces, and one of which was the conference co-chair—Prof. Vic LAW Kam-Tuen, Dr. Tai-chin Lo Associate Professor of Science at HKUST. Law was one of Lee’s postdoctoral students at MIT, and his own research also focuses on the creation and detection of Majorana fermions in topological superconductors. As the Founding President of the Hong Kong Young Academy of Sciences, he is deeply indebted to Lee for being one of his life mentors.

“Patrick is one of my most respected teachers who introduced to me the field of topological superconductors. We are still collaborating closely and even my students at HKUST have the precious opportunities to learn from him,” said Law.

While the quest for quantum computers will continue, Lee is certainly passing on the scientific baton to the next generation in the chase.



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Prof. Patrick A. LEE

Prof. Lee obtained his PhD from MIT in 1970. He then taught at Yale University (1970-1972) and worked at the Theoretical Physics Department of Bell Laboratories (1972-1982). In 1982, he returned to his alma mater and joined the Department of Physics. He is currently the William & Emma Rogers Professor of Physics in MIT.

He has made key contributions to the theory of disordered electronic systems and is a pioneer in mesoscopic physics, the study of small devices at low temperatures. He introduced the concept of universal conductance fluctuations to describe such devices. More recently, his research is focused on the problem of high temperature superconductivity. The starting point of this work is that the new family of superconductors is an example of the doped Mott insulator. The parent material is an antiferromagnetic insulator that is insulating due to correlation effects. Doping introduces carriers into the insulator, leading to a rich variety of novel phenomena including superconductivity. Methods of attack include many-body field theory and numerical work.

Awarded with the Oliver E. Buckley Condensed Matter Physics Prize of the American Physical Society, Lee was elected Member of the US National Academy of Sciences in 1991. In 2005, he received the Dirac Medal from the Abdus Salam International Centre for Theoretical Physics for “his pioneering contributions to our understanding of disordered and strongly interacting many-body systems.”