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<i>Dephrasure</i> Channel and Superadditivity of Coherent Information

Author(s): Felix Leditzky, Debbie Leung, and Graeme Smith
The quantum capacity of a quantum channel captures its capability for noiseless quantum communication. It lies at the heart of quantum information theory. Unfortunately, our poor understanding of nonadditivity of coherent information makes it hard to understand the quantum capacity of all but very s...
[Phys. Rev. Lett. 121, 160501] Published Wed Oct 17, 2018

Secure quantum communication in the presence of phase- and polarization-dependent loss

Author(s): Chenyang Li, Marcos Curty, Feihu Xu, Olinka Bedroya, and Hoi-Kwong Lo
Silicon photonics holds the promise of the miniaturization of quantum communication devices. Recently, silicon chip optical transmitters for quantum key distribution (QKD) have been built and demonstrated experimentally. Nonetheless, these silicon chips suffer substantial phase- and polarization-dep...
[Phys. Rev. A 98, 042324] Published Wed Oct 17, 2018

Geometrical Bounds on Irreversibility in Open Quantum Systems

Author(s): Luca Mancino, Vasco Cavina, Antonella De Pasquale, Marco Sbroscia, Robert I. Booth, Emanuele Roccia, Ilaria Gianani, Vittorio Giovannetti, and Marco Barbieri
Theoretical bounds on irreversible entropy production in a thermalizing quantum system are supported by experiments simulating the thermalization of a qubit using a quantum photonic architecture.
[Phys. Rev. Lett. 121, 160602] Published Wed Oct 17, 2018

Hydrodynamic Diffusion in Integrable Systems

Author(s): Jacopo De Nardis, Denis Bernard, and Benjamin Doyon
We show that hydrodynamic diffusion is generically present in many-body, one-dimensional interacting quantum and classical integrable models. We extend the recently developed generalized hydrodynamic (GHD) to include terms of Navier-Stokes type, which leads to positive entropy production and diffusi...
[Phys. Rev. Lett. 121, 160603] Published Wed Oct 17, 2018

The Intrinsic Structure of Quantum Mechanics. (arXiv:1810.06551v1 [quant-ph])

The wave function in quantum mechanics presents an interesting challenge to
our understanding of the physical world. In this paper, I show that the wave
function can be understood as four intrinsic relations on physical space. My
account has three desirable features that the standard account lacks: (1) it
does not refer to any abstract mathematical objects, (2) it is free from the
usual arbitrary conventions, and (3) it explains why the wave function has its

Matter and spin superposition in vacuum experiment (MASSIVE). (arXiv:1810.07045v1 [quant-ph])

A free-falling nanodiamond containing a nitrogen vacancy centre in a spin
superposition should experience a superposition of forces in an inhomogeneous
magnetic field. We propose a practical design that brings the internal
temperature of the diamond to under 10 K. This extends the expected spin
coherence time from 2 ms to 500 ms, so the spatial superposition distance could
be increased from 0.05 nm to over 1 $\mu$m, for a 1 $\mu$m diameter diamond and
a magnetic inhomogeneity of only 10$^4$ T/m. The low temperature allows

Entanglement studies of interacting fermionic models. (arXiv:1810.06595v1 [cond-mat.stat-mech])

Recent advances in the field of strongly correlated electron systems allow to
access the entanglement properties of interacting fermionic models, by means of
Monte Carlo simulations. We briefly review the techniques used in this context
to determine the entanglement entropies and correlations of the entanglement
Hamiltonian. We further apply these methods to compute the spin two-point
function of entanglement Hamiltonian for a stripe embedded into a correlated

Decoherence allows quantum theory to describe the use of itself. (arXiv:1810.07065v1 [quant-ph])

We show that the quantum description of measurement based on decoherence
fixes the bug in quantum theory discussed in [D. Frauchiger and R. Renner, {\em
Quantum theory cannot consistently describe the use of itself}, Nat. Comm. {\bf
9}, 3711 (2018)]. Assuming that the outcome of a measurement is determined by
environment-induced superselection rules, we prove that different agents acting
on a particular system always reach the same conclusions about its actual
state.

Using and reusing coherence to realize quantum processes. (arXiv:1805.04045v3 [quant-ph] UPDATED)

Coherent superposition is a key feature of quantum mechanics that underlies
the advantage of quantum technologies over their classical counterparts.
Recently, coherence has been recast as a resource theory in an attempt to
identify and quantify it in an operationally well-defined manner. Here we study
how the coherence present in a state can be used to implement a quantum channel
via incoherent operations and, in turn, to assess its degree of coherence. We

Time travel as a Hilbert-space problem. (arXiv:1805.12129v3 [quant-ph] UPDATED)

The issue of time travel can be reduced in quantum theory to an appropriate
Hilbert-space description of feedback loops. I show how to do it in a way that
automatically eliminates problems with chronology protection, provided all
input-output relations are given by unitary maps. Examples of elementary loops
and a two-loop time machine illustrate the construction.