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QUROPE - aggregated feeds in category PhysicsenarXiv.org: Quantum Physics: Recommendation systems with quantum k-NN and Grover's algorithms for data processing. (arXiv:1812.05095v1 [quant-ph])
http://arxiv.org/abs/1812.05095
<p>In this article, we discuss the implementation of a quantum recommendation
system that uses a quantum variant of the k-nearest neighbours algorithm and
the Grover algorithm to search for a specific element in unstructured database.
In addition to the presentation of the recommendation system as an algorithm,
the article also shows a main steps in construction of a suitable quantum
circuit for realisation of a given recommendation system. The computational
complexity of individual calculation steps during recommendation system was
also indicated.<p><a href="http://arxiv.org/abs/1812.05095">read more</a></p>
Fri, 14 Dec 2018 22:03:58 +0100arXiv.org: Quantum Physics: Bell inequalities with one bit of communication. (arXiv:1812.05107v1 [quant-ph])
http://arxiv.org/abs/1812.05107
<p>We study Bell scenarios with binary outcomes supplemented by one bit of
classical communication. We develop a method to find facet inequalities for
such scenarios even when direct facet enumeration is not possible, or at least
difficult. Using this method, we partially solve the scenario where Alice and
Bob choose between three inputs, finding a total of 668 inequivalent facet
inequalities (with respect to relabelings of inputs and outputs).<p><a href="http://arxiv.org/abs/1812.05107">read more</a></p>
Fri, 14 Dec 2018 22:03:58 +0100arXiv.org: Quantum Physics: From the moving piston to the dynamical Casimir effect: explorations with shaken condensates. (arXiv:1812.05114v1 [quant-ph])
http://arxiv.org/abs/1812.05114
<p>Recent experimental realizations of uniform confining potentials for
ultracold atoms make it possible to create quantum acoustic resonators and
explore nonequilibrium dynamics of quantum field theories. These systems offer
a promising new platform for studying the dynamical Casimir effect, since they
allow to achieve relativistic, i.e. near sonic, velocities of the boundaries.
In comparison to previously studied optical and classical hydrodynamic systems
ultracold atoms allow to realize a broader class of dynamical experiments
combining both classical driving and vacuum squeezing.<p><a href="http://arxiv.org/abs/1812.05114">read more</a></p>
Fri, 14 Dec 2018 22:03:58 +0100arXiv.org: Quantum Physics: The role of entropy in topological quantum error correction. (arXiv:1812.05117v1 [quant-ph])
http://arxiv.org/abs/1812.05117
<p>The performance of a quantum error-correction process is determined by the
likelihood that a random configuration of errors introduced to the system will
lead to the corruption of encoded logical information. In this work we compare
two different variants of the surface code with a comparable number of qubits:
the surface code defined on a square lattice and the same model on a lattice
that is rotated by $\pi / 4$.<p><a href="http://arxiv.org/abs/1812.05117">read more</a></p>
Fri, 14 Dec 2018 22:03:58 +0100arXiv.org: Quantum Physics: Stochastic Estimation of Dynamical Variables. (arXiv:1812.05120v1 [quant-ph])
http://arxiv.org/abs/1812.05120
<p>Estimating the parameters governing the dynamics of a system is a
prerequisite for its optimal control. We present a simple but powerful method
that we call STEADY, for STochastic EstimAtion of DYnamical variables, to
estimate the Hamiltonian (or Lindbladian) governing a quantum system of a few
qubits. STEADY makes efficient use of all measurements and it saturates the
information-theoretic limits for such an estimator. Importantly, it is
inherently robust to state preparation and measurement errors.<p><a href="http://arxiv.org/abs/1812.05120">read more</a></p>
Fri, 14 Dec 2018 22:03:58 +0100arXiv.org: Quantum Physics: From asymptotic hypothesis testing to entropy inequalities. (arXiv:1812.05142v1 [quant-ph])
http://arxiv.org/abs/1812.05142
<p>This thesis addresses the interplay between asymptotic hypothesis testing and
entropy inequalities in quantum information theory. In the first part of the
thesis we focus on hypothesis testing. We consider two main settings; one can
either fix quantum states while optimizing over measurements or fix a
measurement and evaluate its capability to discriminate by optimizing over
states. In the former setting, we prove a composite quantum Stein's Lemma. We
also discuss how this gives an operational interpretation to several quantities
of interest.<p><a href="http://arxiv.org/abs/1812.05142">read more</a></p>
Fri, 14 Dec 2018 22:03:58 +0100arXiv.org: Quantum Physics: Interference-induced localization in quantum random walk on clean cyclic graph. (arXiv:1812.05158v1 [quant-ph])
http://arxiv.org/abs/1812.05158
<p>We quantitatively differentiate between the spreads of a discrete-time
quantum random walk and a classical random walk on a cyclic graph. Due to the
closed nature of any cyclic graph, there is additional interference in the
quantum random walk which results in localization of the walker's wavepacket.
We use Shannon entropy to quantify the spread of the walker in both the quantum
and the classical cases.<p><a href="http://arxiv.org/abs/1812.05158">read more</a></p>
Fri, 14 Dec 2018 22:03:58 +0100arXiv.org: Quantum Physics: Post-Newtonian corrections to Schr\"odinger equations in gravitational fields. (arXiv:1812.05181v1 [gr-qc])
http://arxiv.org/abs/1812.05181
<p>In this paper we extend the WKB-like `non-relativistic' expansion of the
minimally coupled Klein--Gordon equation after Kiefer and Singh [1],
L\"ammerzahl [2] and Giulini and Gro{\ss}ardt [3] to arbitrary order in
$c^{-1}$, leading to Schr\"odinger equations describing a quantum particle in a
general gravitational field, and compare the results with canonical
quantisation of a free particle in curved spacetime, following Wajima et al.
[4].<p><a href="http://arxiv.org/abs/1812.05181">read more</a></p>
Fri, 14 Dec 2018 22:03:58 +0100arXiv.org: Quantum Physics: Calculation of molecular vibrational spectra on a quantum annealer. (arXiv:1812.05211v1 [quant-ph])
http://arxiv.org/abs/1812.05211
<p>Quantum computers are ideal for solving chemistry problems due to their
polynomial scaling with system size in contrast to classical computers which
scale exponentially. Until now molecular energy calculations using quantum
computing hardware have been limited to quantum simulators. In this paper, a
new methodology is presented to calculate the vibrational spectrum of a
molecule on a quantum annealer.<p><a href="http://arxiv.org/abs/1812.05211">read more</a></p>
Fri, 14 Dec 2018 22:03:58 +0100arXiv.org: Quantum Physics: Observation of parity-time symmetry breaking in a single spin system. (arXiv:1812.05226v1 [quant-ph])
http://arxiv.org/abs/1812.05226
<p>A fundamental axiom of quantum mechanics requires the Hamiltonians to be
Hermitian which guarantees real eigen-energies and probability conservation.
However, a class of non-Hermitian Hamiltonians with Parity-Time
($\mathcal{PT}$) symmetry can still display entirely real spectra. The
Hermiticity requirement may be replaced by $\mathcal{PT}$ symmetry to develop
an alternative formulation of quantum mechanics. A series of experiments have
been carried out with classical systems including optics, electronics,
microwaves, mechanics and acoustics.<p><a href="http://arxiv.org/abs/1812.05226">read more</a></p>
Fri, 14 Dec 2018 22:03:58 +0100