In a groundbreaking study published in Physical Review Letters, Professor Dong Eon Kim from POSTECH’s Department of Physics and his research team have successfully unraveled the mystery of electron tunneling, a fundamental concept in quantum mechanics. This achievement marks a significant milestone in understanding one of the most enduring enigmas in physics – a phenomenon that has puzzled scientists for over 100 years.

Quantum tunneling is a process where electrons pass through energy barriers (or “walls”) that they seemingly cannot surmount with their energy, much like digging a tunnel through them. This phenomenon underlies the operation of semiconductors, which power smartphones and computers, as well as nuclear fusion – the process that generates light and energy in the sun.

Until now, while some understanding existed about what happens before and after an electron passes through a tunnel, the exact behavior of the electron as it traverses the barrier remained unclear. Enter Professor Kim’s team, who collaborated with researchers from the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, to conduct an experiment using intense laser pulses to induce electron tunneling in atoms.

The results revealed a surprising phenomenon: electrons do not simply pass through the barrier but collide again with the atomic nucleus inside the tunnel. This process was dubbed “under-the-barrier recollision” (UBR) by the research team. Until now, it was believed that electrons could only interact with the nucleus after exiting the tunnel, making this a groundbreaking discovery.

Moreover, during UBR, electrons gain energy inside the barrier and collide again with the nucleus, strengthening what is known as “Freeman resonance.” This ionization process was significantly greater than previously observed and remained largely unaffected by changes in laser intensity – a completely new finding that defied existing theories.

This research marks a crucial step forward in understanding quantum tunneling dynamics. As such, it has significant implications for the development of advanced technologies like semiconductors, quantum computers, and ultrafast lasers, which rely on precise control over electron behavior and increased efficiency.

Professor Kim emphasizes, “Through this study, we’ve found clues about how electrons behave when they pass through the atomic wall.” He concludes, “Now, we can finally understand tunneling more deeply and control it as we wish.”

This research received support from the National Research Foundation of Korea and the Capacity Development Project of the Korea Institute for Advancement of Technology.

Scientists at Harvard University and the Paul Scherrer Institute PSI have made a groundbreaking discovery that could revolutionize our understanding of quantum materials. By using an ultrafast laser technique, they were able to freeze the quantum motion of these materials, paving the way for new technologies such as lossless electronics and high-capacity batteries.

The researchers, led by Matteo Mitrano from Harvard University, used a copper oxide compound called Sr14Cu24O41, which is nearly one-dimensional in structure. This allowed them to study complex physical phenomena that also show up in higher-dimensional systems.

One way to achieve a long-lived non-equilibrium state is to trap it in an energy well from which it does not have enough energy to escape. However, this technique risks inducing structural phase transitions that change the material’s molecular arrangement. Mitrano and his team wanted to avoid this and instead used an alternative approach, where they precisely engineered laser pulses to break the symmetry of electronic states in the compound.

This allowed charges to quantum tunnel from the chains to the ladders, trapping the system in a new long-lived state for some time. The ultra-bright femtosecond X-ray pulses generated at the SwissFEL facility enabled the researchers to catch these ultrafast electronic processes in action and study their properties.

The use of time-resolved Resonant Inelastic X-ray scattering (tr-RIXS) at the SwissFEL Furka endstation gave unique insight into magnetic, electric, and orbital excitations – and their evolution over time. This capability was key to dissecting the light-induced electronic motion that gave rise to the metastable state.

The findings of this study have broad implications for future technologies, including ultrafast optoelectronic devices and non-volatile information storage, where data is encoded in quantum states created and controlled by light.

This work represents a major step forward in controlling quantum materials far from equilibrium, with potential applications in fields such as quantum communication and photonic computing. The use of tr-RIXS at the SwissFEL Furka endstation has opened new scientific opportunities for users, allowing them to study individual and collective excitations in various materials.

The World Health Organization (WHO) reports that antimicrobial resistance causes more than 1 million deaths every year and contributes to over 35 million additional illnesses. Gram-positive pathogens like Staphylococcus aureus and Enterococcus can cause severe hospital-acquired and community-acquired infections, making the development of effective treatments a pressing concern.

Researchers have recently discovered a synthetic compound called infuzide that shows promise against antimicrobial resistant strains of S. aureus and Enterococcus in laboratory and mouse tests. Infuzide was synthesized as part of a decade-long project by interdisciplinary researchers looking for ways to create compounds that could act against pathogens in ways similar to known pharmaceuticals.

“We started the project as a collaboration, looking for ways to synthesize compounds and connecting them with compounds that might have biological activities,” said medicinal chemist Michel Baltas, Ph.D., from the Laboratoire de Chimie de Coordination at the University of Toulouse in France. Baltas co-led the new work, along with Sidharth Chopra, Ph.D., from the CSIR-Central Drug Research Institute in Lucknow, India.

The researchers found that infuzide specifically attacks bacterial cells and is more effective than the standard antibiotic vancomycin in reducing the size of bacterial colonies in lab tests. In tests of resistant S. aureus infections on the skin of mice, the compound effectively reduced the bacterial population, with an even higher reduction when combined with linezolid.

While infuzide did not show significant activity against gram-negative pathogens, the researchers are exploring small changes to expand its antimicrobial activity. The simplicity of the chemical reactions involved in synthesizing infuzide also makes it easy to scale up production for new treatments.

In addition to its potential against multidrug resistance, the group has been investigating the effects of synthesized compounds on other infectious diseases, including tuberculosis. “We have many other candidates to make antimicrobial compounds,” Baltas said.