Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 4 states protocol for time coding quantum key distribution   Coherent one photon pulses are sent with four possible time delays with
respect to a reference. Ambiguity of the photon time detection resulting from
pulses overlap combined with interferometric measurement allows for secure key
exchange.

34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
16
The categories of this paper are: stat
9
The categories of this paper are: nlin
23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg