Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of Rayleigh phonon scattering through excitation of
  extremely high overtones in low-loss cryogenic acoustic cavities for hybrid
  quantum systems   The confinement of high frequency phonons approaching 1 GHz is demonstrated
in phonon-trapping acoustic cavities at cryogenic temperatures using a
low-coupled network approach. The frequency range is extended by nearly an
order of magnitude, with excitation at greater than the 200$^{\text{th}}$
overtone achieved for the first time. Such high frequency operation reveals
Rayleigh-type phonon scattering losses due to highly diluted lattice impurities
and corresponding glass-like behaviour, with a maximum $Q_L\times f$ product of
$8.6\times 10^{17}$ at 3.8K and $4\times10^{17}$ at 15mK. This suggests a limit
on the $Q\times f$ product due to unavoidable crystal disorder. Operation at 15
mK is high enough in frequency that the average phonon occupation number is
less than unity, with a loaded quality factor above half a billion. This work
represents significant progress towards the utilisation of such acoustic
cavities for hybrid quantum systems.

23
The categories of this paper are: solv-int
20
The categories of this paper are: acc-phys
0
The categories of this paper are: hep-ph
36
The categories of this paper are: cmp-lg
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
35
The categories of this paper are: mtrl-th
17
The categories of this paper are: q-fin
29
The categories of this paper are: funct-an
18
The categories of this paper are: econ
11
The categories of this paper are: hep-lat
33
The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
12
The categories of this paper are: nucl-th