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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

- Read more about Aggregating quantum repeaters for the quantum internet
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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.

- Read more about A Mathematical Aspect of Hohenberg-Kohn Theorem. (arXiv:1709.07118v1 [physics.chem-ph])
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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

- Read more about A Practical Quantum Algorithm for the Schur Transform. (arXiv:1709.07119v1 [quant-ph])
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