Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A tunable Josephson platform to explore many-body quantum optics in
  circuit-QED   Coupling an isolated emitter to a single mode of the electromagnetic field is
now routinely achieved and well understood. Current efforts aim to explore the
coherent dynamics of emitters coupled to several electromagnetic modes (EM).
freedom. Recently, ultrastrong coupling to a transmission line has been
achieved where the emitter resonance broadens to a significant fraction of its
frequency. In this work we gain significantly improved control over this
regime. We do so by combining the simplicity of a transmon qubit and a bespoke
EM environment with a high density of discrete modes, hosted inside a
superconducting metamaterial. This produces a unique device in which the
hybridisation between the qubit and up to 10 environmental modes can be
monitored directly. Moreover the frequency and broadening of the qubit
resonance can be tuned independently of each other in situ. We experimentally
demonstrate that our device combines this tunability with ultrastrong coupling
and a qubit nonlinearity comparable to the other relevant energy scales in the
system. We also develop a quantitative theoretical description that does not
contain any phenomenological parameters and that accurately takes into account
vacuum fluctuations of our large scale quantum circuit in the regime of
ultrastrong coupling and intermediate non-linearity. The demonstration of this
new platform combined with a quantitative modelling brings closer the prospect
of experimentally studying many-body effects in quantum optics. A limitation of
the current device is the intermediate nonlinearity of the qubit. Pushing it
further will induce fully developed many-body effects, such as a giant Lamb
shift or nonclassical states of multimode optical fields. Observing such
effects would establish interesting links between quantum optics and the
physics of quantum impurities.

37
The categories of this paper are: supr-con
24
The categories of this paper are: dg-ga
19
The categories of this paper are: eess
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
23
The categories of this paper are: solv-int
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
30
The categories of this paper are: q-alg
2
The categories of this paper are: math
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
3
The categories of this paper are: physics