For years, the scientific community has explored spatial-domain photon number-path entanglement, significant in quantum metrology and information science. This concept involves photons arranged in NOON states, where they are either all in one pathway or another. Applications include super-resolution imaging, the enhancement of quantum sensors, and the development of quantum computing algorithms designed for tasks requiring high phase sensitivity.

In a paper published in Light: Science and Applications, a team of scientists led by Professor Heedeuk Shin from the Department of Physics at Pohang University of Science and Technology in Korea developed entangled states in the frequency domain. Unlike spatial-domain NOON states, where photons are divided between two paths, in this case, they are distributed between two frequencies. This led to the creation of a two-photon NOON state within a single-mode fiber, allowing for two-photon interference with double the resolution of its single-photon counterpart, indicating stability and potential for future applications.

"In our research, we transform the concept of interference from occurring between two spatial paths to taking place between two different frequencies. This shift allowed us to channel both color components through a single-mode optical fiber, creating an unprecedented stable interferometer," Dongjin Lee, the first author of this paper, added.

This discovery enhances our understanding of the quantum world and sets the stage for advancements in quantum information processing in the frequency domain. The exploration of frequency-domain entanglement promises advancements in quantum technologies, potentially impacting quantum sensing and secure communication networks.

Research Report:NOON-state interference in the frequency domain

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