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Quantum mechanics is strictly incompatible with local realism. It has been
shown by Bell and others that it is possible, in principle, to experimentally
differentiate between local realism and quantum mechanics. Numerous experiments
have attempted to falsify local realism; however, they have consistently failed
to close the detection loophole under strict locality conditions, thereby
allowing local realistic explanations for their observations. In 2015, three

The discrete-time quantum walk (QW) is determined by a unitary matrix whose
component is complex number. Konno (2015) extended the QW to a walk whose
component is quaternion.We call this model quaternionic quantum walk (QQW). The
probability distribution of a class of QQWs is the same as that of the QW. On
the other hand, a numerical simulation suggests that the probability
distribution of a QQW is different from the QW. In this paper, we clarify the
difference between the QQW and the QW by weak limit theorems for a class of

Cyber-security has become vital for modern networked control systems (NCS).
In this paper, we propose that the emerging technology of quantum key
distribution (QKD) can be applied to enhance the privacy and security of NCS up
to an unbreakable level. QKD can continuously distribute random secret keys
with much higher privacy between communication parties, and thus enable the
one-time pad encryption that cannot be truly applied in classical networks. We
show that the resulting overall security of NCS can be essentially improved,

We characterize a close connection between the continuous-time quantum-walk
model and a discrete-time quantum-walk version, based on the staggered model
with Hamiltonians in a class of Cayley graphs, which can be considered as a
discretization of continuous-time quantum walks. This connection provides
examples of perfect state transfer and instantaneous uniform mixing in the
staggered model. On the other hand, we provide some more examples of perfect
state transfer and instantaneous uniform mixing in the staggered model that

We extend the Born-Oppenheimer type of approximation scheme for the
Wheeler-DeWitt equation of canonical quantum gravity to arbitrary orders in the
inverse Planck mass squared. We discuss in detail the origin of unitarity
violation in this scheme and show that unitarity can be restored by an
appropriate modification which requires back reaction from matter onto the
gravitational sector. In our analysis, we heavily rely on the gauge aspects of
the standard Born-Oppenheimer scheme in molecular physics.

Logical qubit encoding and quantum error correction (QEC) have been
experimentally demonstrated in various physical systems with multiple physical
qubits, however, logical operations are challenging due to the necessary
nonlocal operations. Alternatively, logical qubits with bosonic-mode-encoding
are of particular interest because their QEC protection is hardware efficient,
but gate operations on QEC protected logical qubits remain elusive. Here, we
experimentally demonstrate full control on a single logical qubit with a

We prove a lower bound on the rate of Greenberger-Horne-Zeilinger states
distillable from pure multipartite states by local operations and classical
communication (LOCC). Our proof is based on a modification of a combinatorial
argument used in the fast matrix multiplication algorithm of Coppersmith and
Winograd. Previous use of methods from algebraic complexity in quantum
information theory concerned transformations with stochastic local operations
and classical operation (SLOCC), resulting in an asymptotically vanishing

We investigate the resonant regime of a mesoscopic cavity made of graphene or
a doped beam splitter. Using Non-Hermitian Quantum Mechanics, we consider the
Bender-Boettcher assumption that a system must obey parity and time reversal
symmetry. Therefore, we describe such system by coupling chirality, parity and
time reversal symmetries through the scattering matrix formalism and apply it
in the shot noise functions, also derived here. Finally we show how to achieve

A continuous-time quantum walk on a graph $X$ is represented by the complex
matrix $\exp (-\mathrm{i} t A)$, where $A$ is the adjacency matrix of $X$ and
$t$ is a non-negative time. If the graph models a network of interacting
qubits, transfer of state among such qubits throughout time can be formalized
as the action of the continuous-time quantum walk operator in the
characteristic vectors of the vertices.

We develop the point of view where Quantum Mechanics results from the
interplay between the quantized number of "modalities" accessible to a quantum
system, and the continuum of "contexts" that are required to define these
modalities. We point out the specific roles of "extracontextuality" and
"extravalence" of modalities, and relate them to the Kochen-Specker and Gleason
theorems.