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The color code is both an interesting example of an exactly solved
topologically ordered phase of matter and also among the most promising
candidate models to realize fault-tolerant quantum computation with minimal
resource overhead. The contributions of this work are threefold. First of all,
we build upon the abstract theory of boundaries and domain walls of topological
phases of matter to comprehensively catalog the objects realizable in color
codes. Together with our classification we also provide lattice representations

The creation of delocalized coherent superpositions of quantum systems
experiencing different relativistic effects is an important milestone in future
research at the interface of gravity and quantum mechanics. This could be
achieved by generating a superposition of quantum clocks that follow paths with
different gravitational time dilation and investigating the consequences on the
interference signal when they are eventually recombined. Light-pulse atom

Many open quantum systems encountered in both natural and synthetic
situations are embedded in classical-like baths. Often, the bath degrees of
freedom may be represented in terms of canonically conjugate coordinates, but
in some cases they may require a non-canonical or non-Hamiltonian
representation. Herein, we review an approach to the dynamics and statistical
mechanics of quantum subsystems embedded in either non-canonical or
non-Hamiltonian classical-like baths which is based on operator-valued

The permutational invariance of identical two-level systems allows for an
exponential reduction in the computational resources required to study the
Lindblad dynamics of coupled spin-boson ensembles evolving under the effect of
both local and collective noise. Here we take advantage of this speedup to
study several important physical phenomena in the presence of local incoherent
processes, in which each degree of freedom couples to its own reservoir.
Assessing the robustness of collective effects against local dissipation is

The classical and quantum mechanical correspondence for constant mass
settings is used, along with some point canonical transformation, to find the
position-dependent mass (PDM) classical and quantum Hamiltonians. The
comparison between the resulting quantum PDM-Hamiltonian and the von Roos
PDM-Hamiltonian implied that the ordering ambiguity parameters of von Roos are
strictly determined. Eliminating, in effect, the ordering ambiguity associated
with the von Roos PDM-Hamiltonian. This, consequently, played a vital role in

In a Quantum Walk (QW) the "walker" follows all possible paths at once
through the principle of quantum superposition, differentiating itself from
classical random walks where one random path is taken at a time. This
facilitates the searching of problem solution spaces faster than with classical
random walks, and holds promise for advances in dynamical quantum simulation,
biological process modelling and quantum computation. Current efforts to
implement QWs have been hindered by the complexity of handling single photons

Vertex amplitudes are elementary contributions to the transition amplitudes
in the spin foam models of quantum gravity. The purpose of this article is make
the first step towards computing vertex amplitudes with the use of quantum
algorithms. In our studies we are focused on a vertex amplitude of 3+1 D
gravity, associated with a pentagram spin-network. Furthermore, all spin labels
of the spin network are assumed to be equal $j=1/2$, which is crucial for the

Weak values have been shown to be helpful especially when considering them as
the outcomes of weak measurements. In this paper we show that in principle, the
real and imaginary parts of the weak value of any operator may be elucidated
from expectation values of suitably defined density, flux and hermitian
commutator operators. Expectation values are the outcomes of strong
(projective) measurements implying that weak values are general properties of
operators in association with pre- and post-selection and they need not be

We describe the design and implementation of a stable high-power 1064 nm
laser system to generate optical lattices for experiments with ultracold
quantum gases. The system is based on a low-noise laser amplified by an array
of four heavily modified, high-power fiber amplifiers. The beam intensity is
stabilized and controlled with a nonlinear feedback loop. Using real-time
monitoring of the resulting optical lattice, we find the stability of the
lattice site positions to be well below the lattice spacing for several hours.

In a recent publication in Nature Communications by Frauchiger and Renner
(Nat. Commun. 9, 3711 (2018)), a Gedankenexperiment was proposed, which was
claimed to be able to lead to inconsistent conclusions with a self-referential
use of quantum theory. Thus it seems to prove that quantum theory cannot
consistently describe the use of itself. Shortly after, Chen and Zhang
suggested an improvement (arXiv:1810.01080) which can made the explanation of