# Resolution in Two-Photon Imaging: A Local Manifestation of Entanglement

## TL;DR

This paper shows how quantum imaging using entangled photons can improve image resolution beyond classical limits.

## Contribution

A practical quantum imaging method achieving a ×2 resolution improvement using bisector positions of photon-pairs.

## Key findings

- Quantum imaging with entangled photons can surpass classical diffraction limits.
- A ×2 improvement in resolution was experimentally demonstrated using bisector positions.
- The method outperforms most previous quantum imaging techniques.

## Abstract

The resolution of
a classical imaging system is limited by diffraction.
This limit can be overcome, for example, by implementing various forms
of localization microscopy in which the center of a fluorescence distribution
is estimated to an accuracy scaling with the square root of the number
of detected photons,
N
. In quantum
imaging the object can be illuminated
using correlated photon-pairs, leading early work to suggest that
a
2
improvement could be obtained
as a result
of averaging the position of N = 2 events. However,
similar to quantum lithography, which relies upon quantum illumination
using entangled photon-pairs and two-photon absorption, the minimum
resolvable feature size is reduced by a factor of 2, not just
2
. Quantum imaging schemes can
also lead
to a factor of 2 improvement. By using a similar source of correlated
photon-pairs to illuminate an object, a single-photon sensitive camera
to detect the photon-pairs, and an image processing algorithm to record
and sum the bisector positions of the transmitted photon-pairs, we
realize a similar factor of ×2 improvement in image resolution,
surpassing that of most earlier quantum imaging work.