We present the design of an inductively shunted transmon qubit with
flux-tunable coupling to an embedded harmonic mode. This circuit construction
offers the possibility to flux-choose between pure transverse and pure
longitudinal coupling, that is coupling to the $\sigma_x$ or $\sigma_z$ degree
of freedom of the qubit. While transverse coupling is the coupling type that is
most commonly used for superconducting qubits, the inherently different
longitudinal coupling has some remarkable advantages both for readout and for

The coupling of atomic arrays and one-dimensional subwavelength waveguides
gives rise to in- teresting photon transport properties, such as recent
experimental demonstrations of large Bragg reflection and paves the way for a
variety of potential applications in the field of quantum non-linear optics.
Here, we present a theoretical analysis for the process of single-photon
scattering in this configuration using a full microscopic approach. Based on
this formalism, we analyze the spectral dependencies for different scattering

Quantum correlations between two free spinless dissipative distinguishable
particles (interacting with a thermal bath) are studied analytically using the
quantum master equation and tools of quantum information. Bath-induced
coherence and correlations in an infinite-dimensional Hilbert space are shown.
We show that for temperature T > 0 the time-evolution of the reduced density
matrix cannot be written as the direct product of two independent particles. We

A decentralized online quantum cash system, called qBitcoin, is given. We
design the system which has great benefits of quantization in the following
sense. Firstly, quantum teleportation technology is used for coin transaction,
which prevents from the owner of the coin keeping the original coin data even
after sending the coin to another. This was a main problem in a classical
circuit and a blockchain was introduced to solve this issue. In qBitcoin, the
double-spending problem never happens and its security is guaranteed

We consider how to quantify non-Gaussianity for the correlation of a
bipartite quantum state by using various measures such as relative entropy and
geometric distances. We first show that an intuitive approach, i.e.,
subtracting the correlation of a reference Gaussian state from that of a target
non-Gaussian state, fails to yield a non-negative measure with monotonicity
under local Gaussian channels. Our finding clearly manifests that quantum-state
correlations generally have no Gaussian extremality. We therefore propose a

Symmetry is one of the most general and useful concepts in physics. A theory
or a system that has a symmetry is fundamentally constrained by it. The same
constraints do not apply when the symmetry is broken. The quantitative
determination of "how much a system breaks a symmetry" allows to reach beyond
this binary situation and is a necessary step towards the quantitative
connection between symmetry breaking and its effects. We introduce measures of
symmetry breaking for a system interacting with external fields (particles).

In a bipartite set-up, the vacuum state of a free Bosonic scalar field is
entangled in real space and satisfies the area-law--- entanglement entropy
scales linearly with area of the boundary between the two partitions. In this
work, we show that the area law is violated in two spatial dimensional model
Hamiltonian having dynamical critical exponent z=3. The model physically
corresponds to next-to-next-to-next nearest neighbour coupling terms on a
lattice. The result reported here is the first of its kind of violation of area

The time evolution of periodically driven non-Hermitian systems is in general
non-unitary but can be stable. It is hence of considerable interest to examine
the adiabatic following dynamics in periodically driven non-Hermitian systems.
We show in this work the possibility of piecewise adiabatic following
interrupted by hopping between instantaneous system eigenstates. This
phenomenon is first observed in a computational model and then theoretically
explained, using an exactly solvable model, in terms of the Stokes phenomenon.

In this review, we provide an introduction and overview to some more recent
advances in real-time dynamics of quantum impurity models and their
realizations in quantum devices. We focus on the Ohmic spin-boson and related
models, which describes a single spin-1/2 coupled to an infinite collection of
harmonic oscillators. The topics are largely drawn from our efforts over the
past years, but we also present a few novel results. In the first part of this

Observables have a dual nature in both classical and quantum kinematics: they
are at the same time \emph{quantities}, allowing to separate states by means of
their numerical values, and \emph{generators of transformations}, establishing
relations between different states. In this work, we show how this two-fold
role of observables constitutes a key feature in the conceptual analysis of
classical and quantum kinematics, shedding a new light on the distinguishing