# All

## Entanglement gain in measurements with unknown results

Author(s): Margherita Zuppardo, Ray Ganardi, Marek Miller, Somshubhro Bandyopadhyay, and Tomasz Paterek
We characterize nonselective global projective measurements capable of increasing quantum entanglement between two particles. In particular, by choosing negativity to quantify entanglement, we show that entanglement of any pure nonmaximally entangled state can be improved in this way (but not of any...
[Phys. Rev. A 99, 042319] Published Wed Apr 10, 2019

## Steady-state entanglement and coherence of two coupled qubits in equilibrium and nonequilibrium environments

Author(s): Zhihai Wang, Wei Wu, and Jin Wang
We analytically and numerically investigate the steady-state entanglement and coherence of two coupled qubits, each interacting with a local boson or fermion reservoir, based on the Bloch-Redfield master equation beyond the secular approximation. We find that there is nonvanishing steady-state coher...
[Phys. Rev. A 99, 042320] Published Wed Apr 10, 2019

## Analytical study of the edge states in the bosonic Haldane model. (arXiv:1704.07746v3 [cond-mat.mes-hall] UPDATED)

We investigate the properties of magnon edge states in a ferromagnetic
honeycomb spin lattice with a Dzyaloshinskii-Moriya interaction (DMI). We
derive analytical expressions for the energy spectra and wavefunctions of the
edge states localized on the boundaries. By introducing an external on-site
potential at the outermost sites, we show that the bosonic band structure is
similar to that of the fermionic graphene. We investigate the region in the
momentum space where the bosonic edge states are well defined and we analyze

## The dynamics of local quantum uncertainty and trace distance discord for two-qubit X states under decoherence: a comparative study. (arXiv:1904.04382v1 [quant-ph])

We employ the concepts of local quantum uncertainty and geometric quantum
discord based on the trace norm to investigate the environmental effects on
quantum correlations of two bipartite quantum systems. The first one concerns a
two-qubit system coupled with two independent bosonic reservoirs. We show that
the trace discord exhibits frozen phenomenon contrarily to local quantum
uncertainty. The second scenario deals with a two-level system, initially
prepared in a separable state, interacting with a quantized electromagnetic

## Purely Quantum Polar Codes. (arXiv:1904.04713v1 [quant-ph])

We provide a purely quantum version of polar codes, achieving the coherent
information of any quantum channel. Our scheme relies on a recursive channel
combining and splitting construction, where random two-qubit Clifford gates are
used to combine two single-qubit channels. The inputs to the synthesized bad
channels are frozen by sharing EPR pairs between the sender and the receiver,
so our scheme is entanglement assisted. We further show that a Pauli channel

## Continuous dynamical decoupling and decoherence-free subspaces for qubits with tunable interaction. (arXiv:1804.03118v3 [quant-ph] UPDATED)

Protecting quantum states from the decohering effects of the environment is
of great importance for the development of quantum computation devices and
quantum simulators. Here, we introduce a continuous dynamical decoupling
protocol that enables us to protect the entangling gate operation between two
qubits from the environmental noise. We present a simple model that involves
two qubits which interact with each other with a strength that depends on their
mutual distance and generates the entanglement among them, as well as in

## Device-independent witnesses of entanglement depth from two-body correlators. (arXiv:1807.06027v3 [quant-ph] UPDATED)

We consider the characterization of entanglement depth in a quantum many-body
system from the device-independent perspective; i.e., certifying how many
particles are genuinely entangled without relying on assumptions on the system
itself nor on the measurements performed. We obtain device-independent
witnesses of entanglement depth (DIWEDs) using the Bell inequalities introduced
in [J. Tura et al., Science 344, 1256 (2014)] and compute their
$k$-producibility bounds. To this end, we present two complementary methods:

## Classical Limits and Contextuality in a Scenario of Multiple Observers. (arXiv:1811.00615v2 [quant-ph] UPDATED)

One of the most surprising features of Quantum Theory is contextuality, which
defies the intuition behind Classical Theories and provides a resource for
quantum computation. However, Classical Theories explain very well our everyday
experience, reinforcing one's believe in a non-contextual explanation of
nature. This naturally raises the question: is it is possible to see the
emergence of non-contextuality under a suitable limit of Quantum Theory? Here
we develop a game of multiple observers inspired by Quantum Darwinism, that

## Spontaneous photon-pair generation at the nanoscale. (arXiv:1903.06956v2 [quant-ph] UPDATED)

Optical nanoantennas have shown a great capacity for efficient extraction of
photons from the near to the far-field, enabling directional emission from
nanoscale single-photon sources. However, their potential for the generation
and extraction of multi-photon quantum states remains unexplored. Here we
demonstrate experimentally the nanoscale generation of two-photon quantum
states at telecommunication wavelengths based on spontaneous parametric
down-conversion in an optical nanoantenna. The antenna is a crystalline AlGaAs

## Bound states in the Brillouin zone continuum. (arXiv:1904.04389v1 [quant-ph])

Systems with space-periodic Hamiltonians have unique scattering properties.
The discrete translational symmetry associated with periodicity of the
Hamiltonian creates scattering channels that govern the scattering process. We
consider a two-dimensional scattering system in which one dimension is a
periodic lattice and the other is localized in space. The scattering and decay
processes can then be described in terms of channels indexed by the Bloch
momentum. We find the 1D periodic lattice can sustain two types of bound states