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Author(s): Koji Azuma and Go Kato
The quantum internet holds promise for accomplishing quantum teleportation and unconditionally secure communication freely between arbitrary clients all over the globe, as well as the simulation of quantum many-body systems. For such a quantum internet protocol, a general fundamental upper bound on ...
[Phys. Rev. A 96, 032332] Published Fri Sep 22, 2017

Author(s): Tymoteusz Salamon and Katarzyna Roszak
We study entanglement generated between a charge qubit and a bosonic bath due to their joint evolution which leads to pure dephasing of the qubit. We tune the parameters of the interaction, so that the decoherence is quantitatively independent of the number of bosonic modes taken into account and in...
[Phys. Rev. A 96, 032333] Published Fri Sep 22, 2017

Quantum criticality usually occurs in many-body systems. Recently it was
shown that the quantum Rabi model, which describes a two-level atom coupled to
a single model cavity field, presents quantum phase transitions from a normal
phase to a superradiate phase when the ratio between the frequency of the two
level atom and the frequency of the cavity field extends to infinity. In this
work, we study quantum phase transitions in the quantum Rabi model from the

High-dimensional encoding of quantum information provides a promising method
of transcending current limitations in quantum communication. One of the
central challenges in the pursuit of such an approach is the certification of
high-dimensional entanglement. In particular, it is desirable to do so without
resorting to inefficient full state tomography. Here, we show how carefully
constructed measurements in two or more bases can be used to efficiently
certify high-dimensional states and their entanglement under realistic

Topological insulators and superconductors at finite temperature can be
characterised by the topological Uhlmann phase. However, a direct experimental
measurement of this invariant has remained elusive in condensed matter systems.
Here, we report a measurement of the topological Uhlmann phase for a
topological insulator simulated by a system of entangled qubits in a
superconducting qubit platform. By making use of ancilla states, otherwise
unobservable phases carrying topological information about the system become

The Hohenberg-Kohn theorem plays a fundamental role in density functional
theory, which has become a basic tool for the study of electronic structure of
matter. In this article, we study the Hohenberg-Kohn theorem for a class of
external potentials based on a unique continuation principle.

Many equations have been introduced and derived by the author indicated in
the title in relation to multi-electron densities between the Hohenberg-Kohn
theorems and variational principle, conversion of the non-relativistic
electronic Schrodinger equation to scaling correct moment functional of ground
state one-electron density to estimate ground state electronic energy,
participation of electron-electron repulsion energy operator in the
non-relativistic electronic Schrodinger equation via the coupling strength

Nonreciprocal microwave devices, such as circulators, are useful in routing
quantum signals in quantum networks and protecting quantum systems against
noise coming from the detection chain. However, commercial, cryogenic
circulators, now in use, are unsuitable for scalable superconducting quantum
architectures due to their appreciable size, loss, and inherent magnetic field.
We report on the measurement of a key nonreciprocal element, i.e., the gyrator,
which can be used to realize a circulator. Unlike state-of-the-art gyrators,

Standard Leggett and Garg inequalities (SLGIs) were formulated for testing
the incompatibility between the classical worldview of macrorealism and quantum
mechanics. In recent times, various other formulations, such as Wigner form of
LGIs (WLGIs), entropic LGIs (ELGIs) and the no-signaling in time (NSIT)
condition have also been proposed. It is also recently argued that no set of
SLGIs can provide the necessary and sufficient conditions for macrorealism but

We describe an efficient quantum algorithm for the quantum Schur transform.
The Schur transform is an operation on a quantum computer that maps the
standard computational basis to a basis composed of irreducible representations
of the unitary and symmetric groups. We simplify and extend the algorithm of
Bacon, Chuang, and Harrow, and provide a new practical construction as well as
sharp theoretical and practical analyses. Our algorithm decomposes the Schur
transform on $n$ qubits into $O(n^4 \log(n/{\epsilon}))$ operators in the