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QUROPE - aggregated feedsenarXiv.org: Quantum Physics: Classification of Non-local Actions: Area versus Volume Entanglement Entropy. (arXiv:1907.09494v1 [hep-th])
http://arxiv.org/abs/1907.09494
<p>From the quantization rules for two classes of non-local actions, we show
that as long as the generalized kinetic energy operator $\hat O(\gamma)$
satisfies $\rm spec\{\hat O(\gamma)\}={\rm spec}\{\hat O\}^\gamma$,(i.e., $\hat
O(\gamma) = \hat O^\gamma$) with $\hat O$ (classically) local, the underlying
action can be mapped onto a purely local theory by a suitable Hilbert-space
transform. In all such cases the partition function is equivalent to that of a
local theory and an area law for the entanglement entropy obtains.<p><a href="http://arxiv.org/abs/1907.09494">read more</a></p>
Wed, 24 Jul 2019 08:22:55 +0200arXiv.org: Quantum Physics: Distributed Quantum Fiber Magnetometry. (arXiv:1907.09516v1 [physics.app-ph])
http://arxiv.org/abs/1907.09516
<p>Nitrogen-vacancy (NV) quantum magnetometers offer exceptional sensitivity and
long-term stability. However, their use to date in distributed sensing
applications, including remote detection of ferrous metals, geophysics, and
biosensing, has been limited due to the need to combine optical, RF, and
magnetic excitations into a single system. Existing approaches have yielded
localized devices but not distributed capabilities. In this study, we report on
a continuous system-in-a-fiber architecture that enables distributed magnetic
sensing over extended lengths.<p><a href="http://arxiv.org/abs/1907.09516">read more</a></p>
Wed, 24 Jul 2019 08:22:55 +0200arXiv.org: Quantum Physics: Topological and subsystem codes on low-degree graphs with flag qubits. (arXiv:1907.09528v1 [quant-ph])
http://arxiv.org/abs/1907.09528
<p>In this work we introduce two code families, which we call the heavy hexagon
code and heavy square code. Both code families are implemented by assigning
physical data and ancilla qubits to both vertices and edges of low degree
graphs. Such a layout is particularly suitable for superconducting qubit
architectures to minimize frequency collision and crosstalk. In some cases,
frequency collisions can be reduced by several orders of magnitude.<p><a href="http://arxiv.org/abs/1907.09528">read more</a></p>
Wed, 24 Jul 2019 08:22:55 +0200arXiv.org: Quantum Physics: Testing fundamental physics with photon frequency shift. (arXiv:1907.09542v1 [gr-qc])
http://arxiv.org/abs/1907.09542
<p>We propose a high precision satellite experiment to further test Einstein's
General Relativity and constrain extended theories of gravity. We consider the
frequency shift of a photon radially exchanged between two observers, one
located on Earth and the other on a satellite in circular orbit in the
equatorial plane.<p><a href="http://arxiv.org/abs/1907.09542">read more</a></p>
Wed, 24 Jul 2019 08:22:55 +0200arXiv.org: Quantum Physics: Steady states, squeezing, and entanglement in intracavity triplet down conversion. (arXiv:1907.09572v1 [quant-ph])
http://arxiv.org/abs/1907.09572
<p>Triplet down conversion, the process of converting one high-energy photon
into three low-energy photons, may soon be experimentally feasible due to
advances in optical resonator technology. We use quantum phase-space techniques
to analyse the process of degenerate intracavity triplet down conversion by
solving stochastic differential equations within the truncated positive-P
representation. The time evolution of both intracavity mode populations are
simulated, and the resulting steady-states are examined as a function of the
pump intensity.<p><a href="http://arxiv.org/abs/1907.09572">read more</a></p>
Wed, 24 Jul 2019 08:22:55 +0200arXiv.org: Quantum Physics: Steganography Protocols for Quantum Channels. (arXiv:1907.09602v1 [cs.IT])
http://arxiv.org/abs/1907.09602
<p>We study several versions of a quantum steganography problem, in which two
legitimate parties attempt to conceal a cypher in a quantum cover transmitted
over a quantum channel without arising suspicion from a warden who intercepts
the cover. In all our models, we assume that the warden has an inaccurate
knowledge of the quantum channel and we formulate several variations of the
steganography problem depending on the tasks used as the cover and the cypher
task.<p><a href="http://arxiv.org/abs/1907.09602">read more</a></p>
Wed, 24 Jul 2019 08:22:55 +0200arXiv.org: Quantum Physics: Experimental proof of Quantum Zeno-assisted Noise Sensing. (arXiv:1907.09618v1 [quant-ph])
http://arxiv.org/abs/1907.09618
<p>In the ideal quantum Zeno effect, repeated quantum projective measurements
can protect the coherent dynamics of a quantum system. However, in the weak
quantum Zeno regime, measurement back-actions can allow the sensing of
semi-classical field fluctuations. In this regard, we theoretically show how to
combine the controlled manipulation of a quantum two-level system, used as a
probe, with a sequence of projective measurements to have direct access to the
noise correlation function.<p><a href="http://arxiv.org/abs/1907.09618">read more</a></p>
Wed, 24 Jul 2019 08:22:55 +0200arXiv.org: Quantum Physics: Analysis of Quantum Approximate Optimization Algorithm under Realistic Noise in Superconducting Qubits. (arXiv:1907.09631v1 [quant-ph])
http://arxiv.org/abs/1907.09631
<p>The quantum approximate optimization algorithm (QAOA) is a promising
quantum-classical hybrid technique to solve combinatorial optimization problems
in near-term gate-based noisy quantum devices. In QAOA, the objective is a
function of the quantum state, which itself is a function of the gate
parameters of a multi-level parameterized quantum circuit (PQC). A classical
optimizer varies the continuous gate parameters to generate distributions
(quantum state) with significant support to the optimal solution.<p><a href="http://arxiv.org/abs/1907.09631">read more</a></p>
Wed, 24 Jul 2019 08:22:55 +0200arXiv.org: Quantum Physics: Asymmetric delay attack on an entanglement-based bidirectional clock synchronization protocol. (arXiv:1907.09661v1 [quant-ph])
http://arxiv.org/abs/1907.09661
<p>We demonstrate an attack on a clock synchronization protocol that attempts to
detect tampering of the synchronization channel using polarization-entangled
photon pairs. The protocol relies on a symmetrical channel, where propagation
delays do not depend on propagation direction, for correctly deducing the
offset between clocks -- a condition that could be manipulated with optical
circulators, which rely on static magnetic fields to break the reciprocity of
propagating electromagnetic fields.<p><a href="http://arxiv.org/abs/1907.09661">read more</a></p>
Wed, 24 Jul 2019 08:22:55 +0200arXiv.org: Quantum Physics: Explaining Retrocausality Phenomena in Quantum Mechanics using a Modified Variational Principle. (arXiv:1907.09688v1 [quant-ph])
http://arxiv.org/abs/1907.09688
<p>A modified lagrangian with causal and retrocausal momenta was used to derive
a causal wave equation and retrocausal wave equation using the principle of
least action. The retrocausal wave function obtained through this method is
equivalent to the complex conjugate of the causal wave equation, thus making
one conclude that retrocausality phenomena was already implicit in classical
quantum mechanics through the means of complex conjugation.<p><a href="http://arxiv.org/abs/1907.09688">read more</a></p>
Wed, 24 Jul 2019 08:22:55 +0200