Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Loschmidt echo in many-spin systems: a quest for intrinsic decoherence
  and emergent irreversibility   If a magnetic polarization excess is locally injected in a crystal of
interacting spins, this "excitation" would spread as consequence of spin-spin
interactions. Such an apparently irreversible process is known as spin
diffusion and it can lead the system back to "equilibrium". Even so, a unitary
quantum dynamics would ensure a precise memory of the non-equilibrium initial
condition. Then, if at certain time, say $t/2$, an experimental protocol
reverses the many-body dynamics, it would drive the system back to the initial
non-equilibrium state at time $t$. As a matter of fact, the reversal is always
perturbed by small experimental imperfections and/or uncontrolled internal or
environmental degrees of freedom. This limits the amount of signal $M(t)$
recovered locally at time $t$. The degradation of $M(t)$ accounts for these
perturbations, which can also be seen as the sources of decoherence. This idea
defines the Loschmidt echo (LE), which embodies the various time-reversal
procedures implemented in nuclear magnetic resonance. Here, we present an
invitation to the study of the LE following the pathway induced by the
experiments. With such a purpose, we provide a historical and conceptual
overview that briefly revisits selected phenomena that underlie the LE
dynamics, ultimately leading to the discussion of irreversibility as an
emergent phenomenon. In addition, we introduce the LE formalism by means of
spin-spin correlation functions and we present new results that could trigger
new experiments and theoretical ideas. In particular, we propose to transform
an initially localized excitation into a more complex initial state, enabling a
dynamically prepared LE. This induces a global definition of the LE in terms of
the raw overlap between many-body wave functions. Our results show that as the
complexity of the prepared state increases, it becomes more fragile towards
small perturbations.

18
The categories of this paper are: econ
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
34
The categories of this paper are: chem-ph
28
The categories of this paper are: alg-geom
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
0
The categories of this paper are: hep-ph
17
The categories of this paper are: q-fin