Quantum Optician Professor Kim Se-jeong's Insights from the Library, Lab, and Boxing Gym

He explained that this habit of going to the library alone while his friends boarded cram school buses led him to the quantum optics lab. He began his lecture by posing a fundamental question about what abilities remain for humans in an era where AI finds the answers.

He said, "I never went to cram school during my school days. When my friends boarded cram school buses after school, I went alone to the neighborhood library."

Professor Kim Se-jeong confessed that his childhood dream was to become a soldier. He mentioned that his father, who was a career soldier, influenced him, and books he read as a child greatly fostered this dream. He stated that he aimed to enter the Korea Military Academy and planned his future accordingly.

He recalled, "When I was little, I wanted to be a soldier. My father, who was a career soldier, influenced me, as did books I read as a child."

He had no idea he had flat feet until his third year of high school and ultimately received a disqualification notice after an X-ray. This unexpected result came as a great shock to him.

Professor Kim conveyed the situation at the time, saying, "After taking an X-ray, I was ultimately disqualified due to flat feet. I didn't even know I had flat feet until my third year of high school."

By reading whatever he could get his hands on in the library instead of going to cram school, he learned to explore the world and ask his own questions. This habit played a crucial role in finding a new direction after his dream of becoming a soldier was thwarted.

He explained, "Life often unfolded differently than planned. Something else moved my life. I never went to cram school during my school days. When my friends boarded cram school buses after school, I went alone to the neighborhood library."

While reading books in the library, Professor Kim Se-jeong learned that even stars like the sun eventually die, which came as a great shock to him as an adolescent. This shock led to fundamental questions about the finitude of life, how the universe works, and the unseen world. He began to hold onto these questions and explore them deeply for a long time.

Professor Kim revealed his thoughts at the time, saying, "I learned that even stars like the sun inevitably stop burning and die someday, which was quite a shock to me as an adolescent. I held onto that shock for a long time. Where do living things go when they die? What happens in the universe? How does the unseen world work?"

After reading this book, he not only developed a desire for space research but also the belief that for such research to be possible, Korea needed to be strong. Based on this realization, he formed a concrete dream of studying physics and weaponry together by entering a military academy.

He mentioned, "It was the book 'The Rose of Sharon Has Bloomed' by Kim Jin-myung. After reading that book, I thought. I had a desire to research space, but more than that, I felt that for such research to be possible, our country needed to be strong. So, I harbored a dream of going to a military academy to study physics and weaponry together."

Even after his dream of becoming a soldier was thwarted, the habit of 'delving deeply into what interests him,' which he acquired in the library, remained. Professor Kim Se-jeong decided to study physics again and entered Sogang University's Department of Physics. While directly handling and operating experimental equipment, he felt the same excitement as when he decided to become a soldier, and he ultimately decided to major in optics, the study of light.

Professor Kim said, "The habit of delving into what interests me, which I developed in the library, remained. Determined to study physics again, I entered Sogang University's Department of Physics. As I directly handled and operated experimental equipment, my heart pounded again, just as it did when I decided to become a soldier. So, I made a decision. To major in optics, the study of light."

This innate curiosity suggests that it led him to the field of optics.

He said, "I think I was always curious about the invisible world. The universe was like that, and so was light."

He stressed that this single, tiny particle of light is deeply connected to future information and communication security.

In the quantum world, the moment someone secretly observes information, the 'superposition' state of the quantum collapses, leaving a trace. Professor Kim Se-jeong explained that the principle of quantum encryption communication is not to prevent eavesdropping itself, but to make it impossible to conceal the fact that eavesdropping occurred, and this is why the technology is fundamentally secure.

He added, "In the quantum world, if someone secretly observes information, the superposition collapses at that moment, leaving a trace. In other words, it's not about preventing eavesdropping, but about making it impossible to conceal the fact that eavesdropping occurred, which is why quantum encryption communication is fundamentally secure."

He said, "For this technology to be possible, a light source that emits light one by one is needed. Researchers call this a single-photon source. It sounds simple, but a common light bulb emits billions of light particles every moment. What we want is exactly the opposite."

To confirm whether tiny light particles, invisible to the eye, are indeed emitted one by one, scientists use an optical device called a 'beam splitter.' A beam splitter is a device like a fork in the road that passes half the light and reflects the other half, with detectors placed at each end. Since light particles cannot be further divided, they invariably choose only one path at the fork. Therefore, the two detectors should never go off simultaneously. If they do, it means the light source is emitting two light particles at a time.

Professor Kim Se-jeong explained, "We count the number of times they go off simultaneously. The closer that number is to zero, the more certain proof it is that photons are indeed being emitted one by one," revealing that this method is used to verify the performance of single-photon sources.

Because the signal from a single light particle is much weaker than ordinary light, the lab is always dark, and researchers must stare at the same spot for days with sensitive detectors. He added that it is common to conduct all-night measurements to capture a good signal.

He explained the difficulties of the research, saying, "I stood before photons driven by curiosity, but the process of answering that curiosity was not at all romantic. Our lab is always dark. The signal from a single light particle is much weaker than ordinary light, so we stare at the same spot for days in a dark room with sensitive detectors. It's common to stay up all night measuring when we catch a good signal."

When Professor Kim Se-jeong was a postdoctoral researcher in a Sydney lab, a graduate student first observed signals of single light particles being emitted even at room temperature from a 2D material called HBN. This discovery became a turning point in research, eliminating the need for equipment to cool down during single-photon source experiments. Professor Kim focused on making this single-photon source brighter.

A brighter single-photon source means that the time it takes for the next light particle to be emitted after one is short. To achieve this, he conducted research utilizing 'optical resonators' smaller than red blood cells, which prevent light from spreading and keep it confined for a long time.

This combination allowed the single-photon source to emit light particles even faster. This is highly significant as it lays the foundation for dramatically increasing data transmission rates in the future quantum communication era.

He emphasized, "Both the optical resonator I made and the single-photon source I mentioned earlier are extremely small and invisible, so combining the two was by no means easy. After four years of countless trials and errors, I finally succeeded in making the single-photon source emit light particles even faster. Just as transmission speed per second is important when we use the internet, being able to send more single-photon sources per second in quantum communication lays the groundwork for dramatically increasing data transmission rates in the future quantum communication era."

He also received the 'Puffy Award,' a prestigious award for emerging scientists in Australia. He commented humbly that as a foreign scientist in Australia with no academic or regional ties, he had not expected any of these results.

Professor Kim modestly stated, "These were unexpected results for a foreign scientist like me in Australia, with no academic or regional ties."

Professor Kim Se-jeong said that the secret to successfully completing difficult experiments was not a single moment of inspiration, but countless failed measurements that were repeated. He emphasized that although there are brilliant colleagues in the lab, what he observed and learned was ultimately the persistence of people who challenged themselves again and again with the same question. He mentioned that he learns this 'power of holding onto a single question for a long time' not only in the lab but also in the boxing gym.

Although there were many days he didn't want to go to the boxing gym, by setting 'just doing it even if I don't want to' as the default, he ended up going every day. Professor Kim added, "I am realizing anew every day in the lab and in front of the boxing gym mirror that a person who masters any field is not someone with special talent, but someone who can repeat the same task."

He emphasized that these three spaces, though seemingly very different, were actually telling the same story.

He said, "I learned how to ask questions in the library, how to find answers in the lab, and the power of repetition in the boxing gym. The three spaces look completely different, but in fact, they were telling the same story."

He acknowledged that machines might now be the fastest to find correct answers, and some problems are solved more accurately and quickly by AI than by humans. However, he emphasized that deciding what questions to ask and whether those questions are truly worth exploring still remains human responsibility.

He explained, "The fastest to find the correct answer might now be machines. Some problems are solved more accurately and quickly by AI than by humans. But deciding what questions to ask, and whether those questions are truly worth exploring, still remains our responsibility," thus asserting the unique role of humans in the AI era.

Professor Kim Se-jeong revealed that he still vividly remembers the day he received the flat foot diagnosis and final disqualification during the physical examination for the Korea Military Academy. At the time, he thought one door in his life had closed, but looking back now, he realized that only the path to becoming a soldier had closed, and instead, that day opened many more doors of opportunity.

He concluded his lecture by saying, "I still vividly remember the scene on the day I was diagnosed with flat feet, receiving the final disqualification in the room with the officers. That day, I thought one door in my life had closed. But looking back now, only the path to becoming a soldier had closed, and that day opened many more doors of opportunity," delivering a hopeful message that setbacks can lead to new opportunities.