Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Contrast inverted ghost imaging with non-interacting photons   Ghost imaging is the remarkable process where an image can be formed from
photons that have not "seen" the object. Traditionally this phenomenon has
required initially correlated but spatially separated photons, e.g., one to
interact with the object and the other to form the image, and has been observed
in many physical situations, spanning both the quantum and classical regimes.
To date, all instances of ghost imaging record an image with the same contrast
as the object, i.e., where the object is bright, the image is also bright, and
vice versa. Here we observe ghost imaging in a new system - a system based on
photons that have never interacted. We utilise entanglement swapping between
independent pairs of spatially entangled photons to establish position
correlations between two initially independent photons. As a consequence of an
anti-symmetric projection in the entanglement swapping process, the recorded
image is the contrast reversed version of the object, i.e., where the object is
bright, the image is dark, and vice versa. The results highlight the importance
of state projection in this ghost imaging process and provides a pathway to
teleporting images across a quantum network.

30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
6
The categories of this paper are: astro-ph
11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
4
The categories of this paper are: cond-mat
20
The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc
18
The categories of this paper are: econ
22
The categories of this paper are: chao-dyn
25
The categories of this paper are: patt-sol
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
1
The categories of this paper are: cs