# NOON-state interference in the frequency domain

## TL;DR

The paper demonstrates quantum interference using NOON states in the frequency domain, enabling enhanced resolution and stable quantum processing.

## Contribution

The paper introduces a novel method to generate and observe two-photon NOON states in the frequency domain using Bragg scattering four-wave mixing.

## Key findings

- Two-photon NOON states are generated in a single-mode fiber using frequency beam splitters.
- The interference pattern shows two-fold enhanced resolution compared to single-photon interference.
- The interferometer exhibits outstanding stability in the frequency domain.

## Abstract

The examination of entanglement across various degrees of freedom has been pivotal in augmenting our understanding of fundamental physics, extending to high dimensional quantum states, and promising the scalability of quantum technologies. In this paper, we demonstrate the photon number path entanglement in the frequency domain by implementing a frequency beam splitter that converts the single-photon frequency to another with 50% probability using Bragg scattering four-wave mixing. The two-photon NOON state in a single-mode fiber is generated in the frequency domain, manifesting the two-photon interference with two-fold enhanced resolution compared to that of single-photon interference, showing the outstanding stability of the interferometer. This successful translation of quantum states in the frequency domain will pave the way toward the discovery of fascinating quantum phenomena and scalable quantum information processing.

We report the NOON-state interference in the frequency domain. Two photons with distinct colors, blue and red, are injected into an interferometer constructed with two frequency beam splitters. The resultant interference pattern is then observed.