The pursuit of creating reliable, efficient, and cost-effective quantum dot sources has taken a significant leap forward with the latest discovery by an international research team. Led by Vikas Remesh from the University of Innsbruck’s Photonics Group, this breakthrough sidesteps limitations in previous approaches that relied on expensive and customized electro-optic modulators.

Visualize a microscopic quantum dot emitting multiple photons with different polarization states, demonstrating the power of stimulated two-photon excitation. The image should convey the elegance of this technique, which moves complexity from electronic components to optical excitation stage, making it more practical for real-world applications.

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The researchers’ innovative approach utilizes stimulated two-photon excitation to generate streams of photons in different polarization states directly from a quantum dot without requiring any active switching components. This method works by exciting the quantum dot with precisely timed laser pulses to create a biexciton state, followed by polarization-controlled stimulation pulses that deterministically trigger photon emission in the desired polarization.

The team’s demonstration of high-quality two-photon states with excellent single-photon properties marks a significant step forward in making quantum dot sources more practical for real-world applications. The technique has immediate implications for secure quantum key distribution protocols and multi-photon interference experiments, which are essential to testing fundamental principles of quantum mechanics.

As noted by Gregor Weihs, head of the photonics research group in Innsbruck, “The study has immediate applications in secure quantum key distribution protocols, where multiple independent photon streams can enable simultaneous secure communication with different parties, and in multi-photon interference experiments which are very important to test even the fundamental principles of quantum mechanics.”

The research represents a collaborative effort involving expertise in quantum optics, semiconductor physics, and photonic engineering. It was supported by the Austrian Science Fund (FWF), the Austrian Research Promotion Agency (FFG), and the European Union’s research programs.

This breakthrough has the potential to revolutionize photonic quantum computing, making it more efficient, cost-effective, and practical for real-world applications. The researchers envision extending this technique to generate photons with arbitrary linear polarization states using specially engineered quantum dots.

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.

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.