Frequency-domain photon number-path entanglement: a new form of quantum entanglement

Unveiling a new quantum frontier.


Spatial-domain photon number-path entanglement is a major actor in quantum metrology and information science and has been studied by scientists for many years.

In this concept, photons are arranged in a NOON state, either in one pathway or another. This enables applications like super-resolution imaging that surpass traditional limits, the enhancement of quantum sensors, and the development of quantum computing algorithms designed for tasks requiring exceptional phase sensitivity.

Scientists have developed entangled states in the frequency domain in a new study. In other words, they have introduced a form of quantum entanglement called frequency-domain photon number-path entanglement.

This idea is similar to spatial-domain NOON states but with a big difference: photons are dispersed across two frequencies rather than two pathways.

NOON-state interference
Experimental setup of the NOON-state interference. PC polarization controller, DL delay line, CF combining filter, CR circulator, NZDSF non-zero dispersion-shifted fiber, BF bandpass filter, FM Faraday mirror, P polarizer, BS beam splitter, D superconducting nanowire single-photon detector. Credit: Light: Science & Applications

This advancement successfully enabled scientists to create a two-photon NOON state within a single-mode fiber. This highlights the ability to perform two-photon interference with double the resolution of its single-photon counterpart, indicating remarkable stability and potential for future applications.

Dongjin Lee, the first author of this paper, said, “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.”

The study could enhance our understanding of the quantum world and set the stage for a new era in quantum information processing in the frequency domain. The investigation of frequency-domain entanglement portends exciting developments in quantum technologies that could influence anything from secure communication networks to quantum sensing.

Journal Reference:

  1. Dongjin Lee et al., NOON-state interference in the frequency domain, Light: Science & Applications (2024). DOI: 10.1038/s41377-024-01439-9


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