Revolutionizing our understanding of light and its interactions, a recent study delves into the realm of quantum optics, where even the interaction of a single light particle with a single atom reveals surprising insights. When light, which is composed of these light particles, travels through space, it does so at the speed of light. However, this speed can vary when the light passes through different materials. This variation is attributed to the refractive index, which accounts for the interaction between the light and the material. By exploring how a single light particle interacts with a two-level atom, this research sheds light on the behavior of light particles and opens new avenues for quantum communication over long distances​​.

In a groundbreaking study, Professor Yuri Rostovtsev, Jacob Emerick, and Professor Anil Patnaik from the University of North Texas and the Air Force Institute of Technology have made a significant advancement in the field of light and atom interactions. Their research, published in “Results in Optics,” explores the interaction of a single light particle with a single atom, a critical phenomenon for the development of long-distance quantum communications.

This research focuses on the basic concepts of light and atom interactions, particularly the way light behaves when it interacts with a single atom. Understanding this interaction is crucial for controlling light in quantum communication systems. The study highlights how light, even at the level of a single light particle and atom, changes its path and properties, crucial for transmitting quantum information over long distances.

A key aspect of this research is the calculation of the different speeds at which the light particle travels and how quickly it can carry information, impacting how quantum information is transmitted and processed. In simpler terms, these speeds determine the rate at which information carried by the light particle can travel and be processed in quantum systems.

Professor Yuri Rostovtsev explains, “We demonstrate the change in the path of a single light particle caused by a single atom that can be detected using the Mach–Zehnder interferometer. This approach allows us to introduce the refractive index for a single light particle that can work for a broad range of applications in quantum fields: from quantum information, quantum computation to imaging and improving microscopy and long-distance quantum communication”​​.

Their findings, using the Mach-Zehnder interferometer, show the change in the path of a single light particle caused by a single atom, a significant advancement in understanding how the refractive index, typically applied in classical optics, is also relevant in the quantum realm. These findings have vast practical applications, extending from quantum computing to enhancing the capabilities of devices like microscopes and long-distance quantum communication.

Additionally, Professor Rostovtsev highlights, “The light particle propagating in the arm with the atom gets an additional change in its path due to interaction with the atom. This change alters the balance of the MZ interferometer and affects the likelihood of the light particle appearing in path 1. The chance to find the light particle in the empty arm of the balanced ZM interferometer is affected. By changing the detuning from the atomic resonance, we observe how the obtained change in the path depends on the detuning, showcasing the behavior of the path change similar to classical light behavior”​​.

In conclusion, the work by Rostovtsev, Emerick, and Patnaik offers significant insights into the interaction between single light particles and atoms, enhancing our understanding of light and atom interactions and laying a solid foundation for future advancements in quantum communication technologies.

Journal Reference

Yuri Rostovtsev, Jacob Emerick, Anil Patnaik, “The refractive index of a single atom experienced by a single photon”, Results in Optics, 2023. DOI: 10.1016/

Image Credit

Image by Ecole polytechnique via Flickr.

About the Authors

Dr. Yuri Rostovtsev is a professor of physics at the University of North Texas, Denton, TX USA, known for his contribution to the quantum coherent effects in various media, ranging from atomic and molecular gases, solids to nucleus. He earned his Master degree in 1983 at the Moscow Institute of Physics and Technology, Moscow, Russia, and his PhD degree in 1991 at the Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. After working in the Institute of Applied Physics of the Russian Academy of Sciences since 1983. In 2009, Dr. Rostovtsev moved to the University of North Texas where he is currently working in the Department of Physics and the Centre of Nonlinear Sciences.

Dr. Yuri Rostovtsev has published more than 200 papers in referred journals, and his research interests lay in atomic and molecular physics, laser spectroscopy, Raman spectroscopy, laser physics, quantum and nonlinear optics, free electron lasers, quantum thermodynamics, quantum information, quantum computers, nanoplasmonincs, nanophotonics, nanomaterials, super-resolution, collective and cooperative excitations and phenomena. He is a senior member of the Optical Society of America. Dr. Rostovtsev received the International Association of Advanced Materials (IAAM) Medal Award for the year 2019, and he was Fulbright Scholar, 2021-2022 (Fulbright Scholarship to Serbia).

Jacob Emerick is a graduate student at the University of North Texas, Denton, TX USA. He is performing research in the field of the quantum and nonlinear optics studying quantum coherent effects in various media. He obtained his Bachelor of Science degree from Baylor University in 2015. In 2018, Mr. Emerick was admitted to the graduate program at the University of North Texas, where he successfully earned his Master’s Degree in 2021. Currently, he is actively engaged in research within the Department of Physics and the Center of Nonlinear Sciences, showcasing his commitment to advancing knowledge in these fields.

Dr. Anil Patnaik is an expert in the theory and experimentation of fundamental laser-matter interactions, both in the realm of classical and quantum regime, and their applications. He received his Master of Science degree in Physics, at Utkal University, Bhubaneswar, India, in 1995 (Specialization in “Solid State Physics”), and he earned his PhD degree from PhD, Physical Research Laboratory, Department of Space, India, in 2001, Thesis title: “Novel optical phenomena induced by external fields.” Dr. Patnaik was JSPS Post-Doctoral Research Associate, University of Electro-Communication, Tokyo, Japan, 2001-2003, and Post-Doctoral Research Associate, Texas A&M University, College Station, TX, 2003-2005.

Dr. Anil Patnaik is an Associate Professor of Physics at Air Force Institute of Technology (AFIT). His specializations include a wide range of topics in quantum optics and quantum information, and on a variety of light-matter interactions applications. He has worked extensively on topics in quantum optics, nonlinear optics and applications and published 50 highly cited journal publications, seven book chapters, and about 200 invited talks and presentations. Amongst other publications, he has authored two extensive reviews on optical sensing applications. One of them has become one of the most cited reviews and earned a top 1% cited engineering journal paper status in “web of science.” Dr. Patnaik received his Ph.D. in quantum optics. He held several academic and visiting positions at prestigious institutions such as Princeton University, Texas A&M, Purdue and Max-Planck Institute for Quantum Optics, Garching, Germany. Recently, Dr. Patnaik received the Distinguished Teaching Professor Award at AFIT. He has been actively involved with numerous professional societies such as the American Physical Society, the Optica (former Optical Society of America), and the American Institute of Aeronautics and Astronautics.