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MCQST awarded physicist Mikhail Lukin the Distinguished Lecturer award in May 2022. We sat down with him to discuss how he began his career and what the future of quantum machines may look like.
Mikhail Lukin: Entering a New Quantum World
When you ask a renowned physicist like Mikhail Lukin how, as a young student, he became aware of the field of quantum technology, he starts by talking about very basics of physics. Only later does he touch upon the great potential and the current hype surrounding quantum computers. But first, the physicist explains in minute detail how important it is to understand the fundamental relationships between photons and atoms—in other words, between light and matter. “These ideas are at the beginning of any kind of quantum machines,” Lukin says. “At that time it was already clear that building a machine like that was going to be quite a tricky business."
Back then, in the mid-1990s, Mikhail Lukin was studying physics. He is now a physics professor at Harvard University and one of the leading quantum physicists in the world. The Russian-born researcher has come to Munich for a public talk and to Garching for workshops on the promising field of quantum technology at the Max Planck Institute of Quantum Optics (MPQ). Even the general public now has palpable expectations when it comes to the topic of quantum computing. And a certain pioneering spirit has also spread among scientists. Many want to be in on the race for spectacular applications, from quantum computers to highly sensitive sensors to quantum cryptography.
During the interview in his guest office in Garching, a couple of young researchers knock on the door. Word has spread that the renowned quantum physicist from Harvard University is visiting Munich for a few days. “I've always liked being in Munich, I’ve spent a lot of time here in my life,” Lukin says, laughing. “We’ve had very cool, exciting collaborations for a number of years.”
Mikhail Lukin studied physics and applied mathematics at the Moscow Institute of Physics and Technology, then went to Texas A&M University, where he completed his doctorate in 1998, and then to Harvard in 2001. He currently works as co-director of the Harvard-MIT Center for Ultracold Atoms and of Harvard Quantum Initiative in Science and Engineering, where he is one of the pioneers for applications of quantum optics for quantum computing purposes. “At Harvard, I always had the freedom to do whatever research I wanted to pursue,” he says. “That’s extremely important, especially for young researchers with lots of ideas. Even now, that’s what I try to pass on to my students: I look for the best people and let them get on with it.” He can now look back on more than 400 publications and a number of notable international awards.
“I always had the freedom to do whatever research I wanted to pursue. That’s extremely important, especially for young researchers with lots of ideas."
The first projects with Ignacio Cirac—an MPQ director who is now also one of the spokespeople for the Cluster of Excellence MCQST—also go back to his early days at Harvard. “The early 2000s were a time of big ideas, a very special time,” recounts Lukin. “We realized that we really could build quantum machines. We didn’t know exactly how, but we felt we could be creative and accomplish something.” He himself had read a “very influential paper” by Cirac back in the mid-1990s. That work, he said, showed him that it would be very difficult, but possible, to one day build such computers. “I knew right away that it was exactly the kind of challenge I wanted to work on,” says Lukin.
Despite all the hype then and now, Lukin also repeatedly puts on the brakes in the interview. It’s easy to forget, he says, that some of the fundamental principles of quantum physics are still very confusing – and quantum phenomena are very tricky to master. “How is it that objects can be in two places at the same time?” The ideas of superposition of states and quantum entanglement are also complicated. But at the same time, this is now well-understood, at least at the microscopic level, he says, laughing.
After saying things like this, Lukin always looks his guest directly in the eye for a few seconds, as if to check whether his explanations and his sense of humor are being followed. The big question, he continues, is whether these unusual quantum effects also occur at the macroscopic level and can thus be harnessed. Can they be used as a source, for example, for transmitting information, for faster computers? It has become a question of the century.
For a long time, it was not clear whether the old, big ideas could actually be implemented. To do so, Lukin explains, you have to manage to isolate the quantum states of individual particles and control them completely. Then you have to build ever larger systems from these particles without losing control over the quantum states.
Every element of a table, for example, has quantum properties, says Lukin, gently tapping on the desk in the guest office. But they tend to disappear when the atoms come together to form a table. “Look, you’re not going to see superposition here anymore, you're not going to see Schrödinger’s cat here either,” he says, alluding to the famous thought experiment by Austrian physicist Erwin Schrödinger. In it, Schrödinger illustrated the challenges of understanding quantum mechanics, whose principles are not so easily transferable to everyday life.
So, he says, it’s important not to lose control of quantum states if you want to build larger machines in real life, such as quantum computers. “Nobody knows if we’ll ever be able to do that,” says Lukin. “And even if we do succeed, we don’t at all know what we’ll be able to do with these computers.” A quantum computer is not just a faster computer, and many people don’t understand that. So, he always says, “Wait a second. We may be at the dawn of a new era, but we don’t know what we can accomplish!” The door is open, but it also takes you into completely unknown territory.
Responsible researchers like Lukin are therefore also concerned about balancing hype and overblown expectations. At the same time, he and his team at Harvard are making great strides in advancing their system of a quantum simulator; he, too, is in the quantum race, so he is definitely familiar with the “euphoria” side. Last year, he published a noteworthy paper in the journal Nature about a quantum simulator with 256 qubits, the largest of its kind to date. The key here is that the individual qubits, or quantum bits, are programmable. “We’re starting to build machines that get bigger, retain quantum properties, and are programmable,” he says. “That opens the door to scientific questions that we haven’t been able to address before. And it pushes the field to a new level; no one has ever come this far,” says Lukin confidently. “We're entering a whole new realm of the quantum world.”
The beginnings are promising. The physicist believes that systems with up to 1,000 qubits will soon be achievable. The challenges are growing in the extreme. “As you increase the number of qubits, you have to improve control over them,” Lukin says. “That's extremely difficult, but we are learning as we play with the systems.”
Often, this does not initially result in new supercomputers but in new tools. Lukin’s team, for example, is able to specifically manipulate individual atoms with lasers. To do this, he uses devices such as optical tweezers—a key component of Lukin’s quantum machine. They can be used to hold and move tiny objects using light. When you talk to Lukin about such things, you get a sense of what he means by control in detail: it is control at the atomic level.
It's also the possible beginning of quantum logic—the possibility of actually programming individual qubits. Lukin slows down here, however, and references the point in development we are currently in. “I like to compare this to classical computers in the 1950s,” says Lukin. “It also took decades before people could do anything useful with computers.”
Perhaps quantum computers will never be able to compute in the classical sense. “In the beginning, such quantum machines will likely solve problems that don't seem important to everyone,” says Lukin mischievously. You could observe quantum phase transitions in many-particle systems or explore what are called lattice gauge theories, important fundamental topics, he says. But some systems could also be used as highly sensitive sensors and materials such as graphene could be better studied, or even individual molecules could be observed. And physicists could even learn to understand complex physical phenomena such as superconductivity or magnetism when smaller systems become larger ones and under certain circumstances, which have yet to be clarified, materials suddenly become magnetic or are able to conduct electricity without losses. For physicists, these are milestones, not yet a quantum computer as some people expect. But they are great strides into a new age—an era that Lukin sensed was dawning as a young student.
MCQST Speaker Ignacio Cirac presents Mikhail Lukin with the MCQST Distinguished Lecturer Award.
Mikhail Lukin was MCQST Distinguished Lecturer in 2022. As part of this program, he gave a public lecture at the Literaturhaus München. You can watch the video here: