Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Witnessing quantumness of a system by observing only its classical
  features   Witnessing non-classicality in the gravitational field has been claimed to be
practically impossible. This constitutes a deep problem, which has even lead
some researchers to question whether gravity should be quantised, due to the
weakness of quantum effects. To counteract these claims, we propose a thought
experiment that witnesses non-classicality of a physical system by probing it
with a qubit. Remarkably, this experiment does not require any quantum control
of the system, involving only measuring a single classical observable on that
system. In addition, our scheme does not even assume any specific dynamics.
That non-classicality of a system can be established indirectly, by coupling it
to a qubit, opens up the possibility that quantum gravitational effects could
in fact be witnessed in the lab.

16
The categories of this paper are: stat
2
The categories of this paper are: math
23
The categories of this paper are: solv-int
26
The categories of this paper are: bayes-an
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
4
The categories of this paper are: cond-mat
37
The categories of this paper are: supr-con
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
27
The categories of this paper are: comp-gas
5
The categories of this paper are: gr-qc
25
The categories of this paper are: patt-sol