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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

- Read more about qBitcoin: A Peer-to-Peer Quantum Cash System. (arXiv:1708.04955v2 [q-fin.GN] UPDATED)
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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