# Sub-Attosecond Metrology via X-Ray Hong-Ou-Mandel Effect

## TL;DR

This paper proposes a method using Hong-Ou-Mandel interference with x-rays to measure delays and path differences at sub-attosecond precision, enabling ultra-high precision quantum measurements at x-ray wavelengths.

## Contribution

It introduces a novel scheme combining broadband x-ray photon pairs and multilayer interferometry for ultra-precise quantum metrology.

## Key findings

- Measurement precision better than 0.1 attoseconds
- Correlation time of photon pairs shorter than 1 attosecond
- Potential for advanced quantum measurement techniques at x-ray wavelengths

## Abstract

We show that sub-attosecond delays and sub-Angstrom optical path differences can be measured by using Hong-Ou-Mandel interference measurements with x-rays. We propose to use a system comprising a source based on spontaneous parametric down-conversion for the generation of broadband x-ray photon pairs and a multilayer-based interferometer. The correlation time of the photon pairs and the Hong-Ou-Mandel dip are shorter than 1 attosecond, hence the precision of the measurements is expected to be better than 0.1 attosecond. We anticipate that the scheme we describe in this work will lead to the development of various techniques of quantum measurements with ultra-high precision at x-ray wavelengths.

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Source: https://tomesphere.com/paper/1908.01592