Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Violation of a Leggett-Garg inequality with ideal non-invasive
  measurements   The quantum superposition principle states that an entity can exist in two
different states simultaneously, counter to our 'classical' intuition. Is it
possible to understand a given system's behaviour without such a concept? A
test designed by Leggett and Garg can rule out this possibility. The test,
originally intended for macroscopic objects, has been implemented in various
systems. However to-date no experiment has employed the 'ideal negative result'
measurements that are required for the most robust test. Here we introduce a
general protocol for these special measurements using an ancillary system which
acts as a local measuring device but which need not be perfectly prepared. We
report an experimental realisation using spin-bearing phosphorus impurities in
silicon. The results demonstrate the necessity of a non-classical picture for
this class of microscopic system. Our procedure can be applied to systems of
any size, whether individually controlled or in a spatial ensemble.

8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
27
The categories of this paper are: comp-gas
4
The categories of this paper are: cond-mat
9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
6
The categories of this paper are: astro-ph
14
The categories of this paper are: math-ph
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
29
The categories of this paper are: funct-an
24
The categories of this paper are: dg-ga
30
The categories of this paper are: q-alg