Ask a Caltech Expert: Nai-Chang Yeh on New Materials and the Future of Quantum Technology
This article was reviewed by a Caltech faculty member.
As part of Conversations on the Quantum World, a webinar series hosted by the Caltech Science Exchange, Nai-Chang Yeh, Caltech’s Thomas W. Hogan Professor of Physics, discusses what quantum materials are and why we can expect to find them in future technologies.
Yeh, who previously co-directed Caltech's Kavli Nanoscience Institute, invents powerful tools and approaches to study and engineer materials at the tiny scale of billionths of a meter. She investigates materials with fascinating quantum properties, such as superconductors, exotic magnets, graphene, topological materials, and materials made of atomically thin sheets or wires.
In conversation with Caltech writer Ann Motrunich, Yeh explains the special tools and techniques needed to conduct research at the nanoscale, and describes the powerful potential of quantum materials to transform the future of computation, sustainability, medicine, and other fields.
Highlights from the conversation are below.
The questions and answers below have been edited for clarity and length.
When engineers and physicists make new materials in electronics, what sizes are they working with?
Typically, the sizes people are working with these days are mostly at the nanoscale or nanometer scale, which is a few billionths of a meter—a scale that's related to the size of molecules, or a few tens of atoms. To work at this very small scale, special tools and techniques are needed. You need special tools to image the tiny structures or even to fabricate devices. Some of the techniques include electron beam microscopy, lithography, focus ion beam microscopy, and lithography. There are other things like scanning tunneling microscopy, atomic force microscopy, nano-scanning optical microscopy. Given the tiny sizes of these things—they're even smaller than typical dust particles—people often will have to conduct observations and fabrication in a clean-room environment.
What are quantum materials?
Let me start with a little historical background. "Quantum materials" was a phrase originally invented by researchers in condensed matter physics. It's an umbrella term referring to materials that have properties that cannot be easily described by classical, or low-level, quantum physics. Nowadays people generalize quantum materials to other things, including topological materials, low-dimensional materials, and engineered quantum materials. (Note: Find a more in-depth discussion of these materials in the Conversation recording). The definition of "quantum materials" these days is much broader than when the term was originally created.
How are quantum materials useful? How might we use them in the future?
Right now, for instance, one of the major challenges in advancing semiconducting technology is that we need to continually decrease the size of nano-electronic components and devices. That leads to new challenges in the quantum limit. For instance, we have issues related to quantum conductance, quantum capacitance, quantum fluctuations as well as increasing heat dissipation. Now, if we incorporate quantum materials, we can actually introduce additional electrical and thermal conduction channels and provide protection barriers and layers to prevent atomic migration in nano devices and nano structures. These materials also have interesting properties you can use to develop additional functionalities.
All of these can lead to devices with better operation efficiency, faster speed, and lower energy consumption for smaller and smaller volumes. That's becoming an important challenge, at least for nano-electronic applications. Of course, there are many other areas of applications. Quantum materials are not only useful for quantum technology but also for a wide range of applications, such as metrology, sustainability, biomedical and environmental applications, communications, and consumer products. (Note: Find a more in-depth discussion of these applications in the Conversation recording).
Is there a link between quantum materials and quantum computers?
Kind of. Let me elaborate. As you know, to make quantum computers you need to start with qubits, also known as "quantum bits." And not just quantum bits, you also need to have quantum memories, quantum networks, quantum transducers—all of those things. But the most essential part is the quantum bits. Currently, those qubits are mostly made of superconductors, but they're very low-temperature superconductors. There are many issues with that. They only operate at very, very low temperatures. That makes these qubits not very scalable. If we can advance interesting and good properties of higher-temperature superconductors, then it can certainly help the development of qubits.
Also, there are qubits already made of quantum materials. For example, people have used semiconductor quantum dots and cooled atoms as qubits. So, these are examples of real quantum materials already being used as qubits. And of course, qubits are directly related to quantum computation.
Typical quantum dots and cooled atoms are not as well developed as the low-temperature superconducting qubits for quantum computation right now. But the application of quantum materials to qubits is certainly an area that can have impact on quantum computation.
How different might the future look if we can really turn the physics to our advantage here?
I would say that we could see a new quantum era with scalable quantum computers and quantum networks. That would mean fast computation and many new possibilities for technology. You might have better, faster, smarter, and smaller electronics; photonic sensors and other instruments for scientific exploration. You might use quantum technologies in consumer products, medicine, or even national security. You could also have more efficient energy and larger energy storage capabilities for a greener environment. There are many potential good things related to everyday life, research, and sustainability.
You studied under Mildred Dresselhaus, a leader in nanotechnology, carbon science, and electronics. What was the most valuable thing you learned from her?
Mildred Dresselhaus was the first tenured woman professor in electrical engineering and physics at MIT, and also the first institute professor at MIT. She won many honors, including the National Medal of Science, the Buckley Prize for Condensed Matter Physics, the Kavli Prize for Nanoscience, and also the Presidential Medal of Freedom. She was also the director of Department of Energy Office of Science for some time. So, she made enormous contributions to the world. She was always very dedicated to everything she did, and she was passionate about research. Most of all she was incredibly kind and generous to people.
She achieved a pinnacle of great scholarship. In Chinese culture, we regard the pinnacle of scholarship as a person's highest accomplishment. There are three important ingredients associated with that accomplishment, in my opinion. They are virtuosity, versatility, and virtue. Millie accomplished virtuosity in her career, but she was also very versatile. In particular, she was a fine amateur musician. She played violin and viola. And then virtue. In Eastern culture, we consider that highly, and there is no doubt in my mind that Millie was highly virtuous.
She was a great role model to all of us who interacted with her, whether we were her students or not.
Here are some of the other topics addressed in the video linked above:
- Does any of today's technology already make use of quantum materials?
- What are some particularly exciting future applications of quantum materials?
- Will quantum materials fully replace old technology?
- What factors should investors consider when evaluating start-ups focused on quantum materials?
- Are researchers considering quantum biological processes, such as photosynthesis, as a source of inspiration for new technologies?
Learn more about the quantum world on the Caltech Science Exchange: