Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Active and Passive Quantum Erasers for Neutral Kaons   Quantum marking and quantum erasure are discussed for the neutral kaon
system. Contrary to other two-level systems, strangeness and lifetime of a
neutral kaon state can be alternatively measured via an "active" or a "passive"
procedure. This offers new quantum erasure possibilities. In particular, the
operation of a quantum eraser in the "delayed choice" mode is clearly
illustrated.

33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
14
The categories of this paper are: math-ph
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
25
The categories of this paper are: patt-sol
30
The categories of this paper are: q-alg
11
The categories of this paper are: hep-lat