Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Revealing higher-order light and matter energy exchanges using quantum
  trajectories in ultrastrong coupling   The dynamics of open quantum systems is often modelled using master
equations, which describe the expected outcome of an experiment (i.e., the
average over many realizations of the same dynamics). Quantum trajectories,
instead, model the outcome of ideal single experiments -- the ``clicks'' of a
perfect detector due to, e.g., spontaneous emission. The correct description of
quantum jumps, which are related to random events characterizing a sudden
change in the wave function of an open quantum system, is pivotal to the
definition of quantum trajectories. In this article, we extend the formalism of
quantum trajectories to open quantum systems with ultrastrong coupling (USC)
between light and matter by properly defining jump operators in this regime. In
such systems, exotic higher-order quantum-state- and energy-transfer can take
place without conserving the total number of excitations in the system. The
emitted field of such USC systems bears signatures of these higher-order
processes, and significantly differs from similar processes at lower coupling
strengths. Notably, the emission statistics must be taken at a single quantum
trajectory level, since the signatures of these processes are washed out by the
``averaging'' of a master equation. We analyze the impact of the chosen
unravelling (i.e., how one collects the output field of the system) for the
quantum trajectories and show that these effects of the higher-order USC
processes can be revealed in experiments by constructing histograms of detected
quantum jumps. We illustrate these ideas by analyzing the excitation of two
atoms by a single photon~[Garziano et al., Phys. Rev. Lett.117, 043601 (2016)].
For example, quantum trajectories reveal that keeping track of the quantum
jumps from the atoms allow to reconstruct both the oscillations between one
photon and two atoms, as well as emerging Rabi oscillations between the two
atoms.

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The categories of this paper are: physics
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
32
The categories of this paper are: atom-ph
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The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
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The categories of this paper are: math-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: cs
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The categories of this paper are: patt-sol
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The categories of this paper are: alg-geom
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The categories of this paper are: adap-org
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The categories of this paper are: q-alg
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The categories of this paper are: plasm-ph
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The categories of this paper are: nucl-th