Scientists who change the ‘feelings’ of quantum

You might not have ever felt the vibration caused by cars passing in and out of a parking lot next to a building. Most people don't even feel the vibration that occurs when flushing the toilet. However, some laboratories cannot tolerate even these minor vibrations that humans cannot feel.

Sunny Kim, the Outreach Manager at the IBS Center for Quantum Nanoscience (QNS), who was walking down the aisle with the reporter, explained, “The scanning tunneling microscope (STM) in the experimental building is also affected by vibrations from parking lots and restrooms.” She continued, “So, after separating the experimental building and the main building, we connected them through a short bridge we just passed.”

The main research task of QNS is to reveal the quantum characteristics of atoms and molecules using STM. The photos hanging on the walls of the laboratory show the achievements so far at a glance. All of them are atoms and molecules observed by QNS’s STMs. The STM works by holding a metallic needle 1-2 atom diameters away from the sample. Any shaking of the tip, even atomic size shaking, disturbs this incredibly precise tool. Pointing to the atoms in the frame, Kim explained, “Observing atoms with STM is an extremely precise technique. Controlling the atom with the STM tip is as hard as rolling a ball with a long stick that is about the distance from Seoul to Busan.”

Particles with happy or unhappy moods

The reason why QNS is immersed in precise STM observation is to solve fundamental questions about the ‘qubit’, the basic operation unit of quantum computers. At the same time, research is also being conducted to point out the direction that qubits should go.

“Quantum computers use quantum entanglement between qubits to perform computing,” said Dr. Wonjun Jang, a researcher at QNS. “However, current science has not yet fully understood the entanglement phenomenon.” The qubits themselves also have a lot to improve on. “One of the current problems in the field of quantum computing is that qubits are very sensitive to the external environment,” said Jang.

Quantum entanglement is one of the fundamental properties of quantum. Scientists have devised various metaphors to explain the mysterious particle defined as quantum. Among the analogies the reporter heard, the one that nodded the most was the metaphor of Dr. Fabio Donati, the leader of the ESR-Ensemble Team.

“Quantum states are like human feelings. Sometimes I happy, and sometimes I feel unhappy. Anyway, in between, there is a vague emotional superposition that I am both happy and unhappy.”

These happy-and-unhappy mood states resemble a quantum superposition of both states at the same time. However, our feelings are sometimes determined by the moods of the people around us. When people close to me feel happy, I may feel happy too. Quantum entanglement is the interconnection of quantum states between multiple quanta. When the state of one of the two entangled quanta is determined, the state of the other quanta is also determined accordingly.

Controlling the quantum’s feelings

To control the 'mood' of quantum, QNS added one function to STM. Team leader Dr. Soo-hyun Phark said, “The quantum state that QNS explores is the spin of a particle. The spin of a particle can be changed using electron spin resonance (ESR), which occurs when an oscillating electric field is applied.” This state in which the spin of a particle can be controlled using an external electric field is called “quantum coherence.”

ESR-STM, developed by QNS is cutting-edge equipment that can change the spin state of particles by controlling quantum coherence. It was created by improving the world’s first ESR-STM, which was developed by Director Andreas Heinrich when he was at IBM by. Phark said, “We took one more step forward from IBM’s ESR-STM, which could not change the direction of the magnetic field. Here at QNS, we can change the magnetic field’s direction according to the particle we want to study.” Another point of improvement is the ability to obtain cleaner observation results by reaching 90% lower temperature than before.”

Director Heinrich said, “I have spent more than 20 years studying how individual atoms and molecules behave on surfaces,” and added, “We have also succeeded in measuring the spin of a single atom for the first time in the world.” He said, “My experimental approach opens up a new world in which we can observe single atoms and single molecules, position them with incredible precision, and even measure their quantum states.” 

He also expressed his vision for the center’s future. “With our research at QNS, Korea is currently leading the world in quantum nanoscience on surfaces. We look forward to continuing our groundbreaking research.”