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Space QUEST mission proposal: Experimentally testing decoherence due to gravity. (arXiv:1703.08036v1 [quant-ph])

Models of quantum systems on curved space-times lack sufficient experimental
verification. Some speculative theories suggest that quantum properties, such
as entanglement, may exhibit entirely different behavior to purely classical
systems. By measuring this effect or lack thereof, we can test the hypotheses
behind several such models. For instance, as predicted by Ralph and coworkers
[T C Ralph, G J Milburn, and T Downes, Phys. Rev. A, 79(2):22121, 2009; T C

Limits on manipulating conditional photon statistics via interference of weak lasers. (arXiv:1703.08053v1 [quant-ph])

Photon anti-bunching, measured via the Hanbury-Brown-Twiss experiment, is one
of the key signatures of quantum light and is tied to sub-Poissonian photon
number statistics. Recently, it has been reported that photon anti-bunching or
conditional sub-Poissonian photon number statistics can be obtained via
second-order interference of mutually incoherent weak lasers and heralding
based on photon counting. Here, we report theoretical analysis on the limits of

A note on the gap between rank and border rank. (arXiv:1504.05597v2 [math.AC] UPDATED)

We study the tensor rank of the tensor corresponding to the algebra of
n-variate complex polynomials modulo the dth power of each variable. As a
result we find a sequence of tensors with a large gap between rank and border
rank, and thus a counterexample to a conjecture of Rhodes. At the same time we
obtain a new lower bound on the tensor rank of tensor powers of the generalised
W-state tensor. In addition, we exactly determine the tensor rank of the tensor

Spin in the extended electron model. (arXiv:1703.08076v1 [physics.gen-ph])

It has been found that a model of extended electrons is more suited to
describe theoretical simulations and experimental results obtained via scanning
tunnelling microscopes, but while the dynamic properties are easily
incorporated, magnetic properties, and in particular electron spin properties
pose a problem due to their conceived isotropy in the absence of measurement.
The spin of an electron reacts with a magnetic field and thus has the
properties of a vector. However, electron spin is also isotropic, suggesting

Criteria for universality of quantum gates. (arXiv:1610.00547v5 [quant-ph] UPDATED)

We consider the problem of deciding if a set of quantum one-qudit gates
$\mathcal{S}=\{U_1,\ldots,U_n\}$ is universal. We provide the compact form
criteria leading to a simple algorithm that allows deciding universality of any
given set of gates in a finite number of steps. Moreover, for a non-universal
$\mathcal{S}$ our criteria indicate what type of gates can be added to
$\mathcal{S}$ to turn it into a universal set.

Suppressing and restoring the Dicke superradiance transition by dephasing and decay. (arXiv:1611.03342v2 [cond-mat.quant-gas] UPDATED)

We show that dephasing of individual atoms destroys the superradiance
transition of the Dicke model, but that adding individual decay toward the spin
down state can restore this transition. To demonstrate this, we present a
method to give an exact solution for the $N$ atom problem with individual
dephasing which scales polynomially with $N$. By comparing finite size scaling
of our exact solution to a cumulant expansion, we confirm the destruction and
restoration of the superradiance transition holds in the thermodynamic limit.

Quantum state atomic force microscopy. (arXiv:1703.08077v1 [quant-ph])

New classical modalities of atomic force microscopy continue to emerge to
achieve higher spatial, spectral, and temporal resolution for nanometrology of
materials. Here, we introduce the concept of a quantum mechanical modality that
capitalizes on squeezed states of probe displacement. We show that such
squeezing is enabled nanomechanically when the probe enters the van der Waals
regime of interaction with a sample. The effect is studied in the non-contact

Boltzmann entropy of a Newtonian Universe. (arXiv:1703.08082v1 [quant-ph])

A dynamical estimate is given for the Boltzmann entropy of the Universe,
under the simplifying assumptions provided by Newtonian cosmology. We first
model the cosmological fluid as the probability fluid of a quantum-mechanical
system. Next, following current ideas about the emergence of spacetime, we
regard gravitational equipotentials as isoentropic surfaces. Therefore
gravitational entropy is proportional to the vacuum expectation value of the
gravitational potential in a certain quantum state describing the matter

Belief-Invariant and Quantum Equilibria in Games of Incomplete Information. (arXiv:1605.07896v3 [cs.GT] UPDATED)

Drawing on ideas from game theory and quantum physics, we investigate
nonlocal correlations from the point of view of equilibria in games of
incomplete information. These equilibria can be classified in decreasing power
as general communication equilibria, belief-invariant equilibria and correlated
equilibria, all of which contain the familiar Nash equilibria. The notion of
belief-invariant equilibrium has appeared in game theory before, in the 1990s.
However, the class of non-signalling correlations associated to

Anomalies and entanglement renormalization. (arXiv:1703.07782v1 [quant-ph])

We study 't Hooft anomalies of discrete groups in the framework of
(1+1)-dimensional multiscale entanglement renormalization ansatz states on the
lattice. Using matrix product operators, general topological restrictions on
conformal data are derived. An ansatz class allowing for optimization of MERA
with an anomalous symmetry is introduced. We utilize this class to numerically
study a family of Hamiltonians with a symmetric critical line. Conformal data
is obtained for all irreducible projective representations of each anomalous