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QUROPE - aggregated feeds in category PhysicsenarXiv.org: Quantum Physics: Can Quantum discord increase in a quantum communication task?. (arXiv:1808.04363v1 [quant-ph])
http://arxiv.org/abs/1808.04363
<p>Quantum teleportation of an unknown quantum state is one of the few
communication tasks which has no classical counterpart. Usually the aim of
teleportation is to send an unknown quantum state to a receiver. But is it
possible in some way that the receiver's state has more quantum discord than
the sender's state? We look at a scenario where Alice and Bob share a pure
quantum state and Alice has an unknown quantum state. She performs joint
measurement on her qubits and channel to prepare Bob's qubits in a mixed state
which has higher quantum discord than hers.<p><a href="http://arxiv.org/abs/1808.04363">read more</a></p>
Wed, 15 Aug 2018 17:04:11 +0200arXiv.org: Quantum Physics: Sensitivity of quantum information to environment perturbations measured with the out-of-time-order correlation function. (arXiv:1808.04375v1 [quant-ph])
http://arxiv.org/abs/1808.04375
<p>Measures to quantify the flow of quantum information and its sensitivity to
environment perturbations are needed to better understand the evolution of open
quantum systems and to distinguish non-Markovian from Markovian dynamics. Here,
we show that the extent of correlations in many-body quantum systems is an
experimentally accessible metric for quantifying the spread of quantum
information. Our experiment applies multiple-quantum nuclear magnetic resonance
(NMR) technique to take snapshots of the multi-spin correlations between a
central spin and the spins in its surrounding environment.<p><a href="http://arxiv.org/abs/1808.04375">read more</a></p>
Wed, 15 Aug 2018 17:04:11 +0200arXiv.org: Quantum Physics: Singularity in Entanglement Negativity Across Finite Temperature Phase Transitions. (arXiv:1808.04381v1 [cond-mat.stat-mech])
http://arxiv.org/abs/1808.04381
<p>Phase transitions at a finite (i.e. non-zero) temperature are typically
dominated by classical correlations, in contrast to zero temperature
transitions where quantum mechanics plays an essential role. Therefore, it is
natural to ask if there are any signatures of a finite temperature phase
transition in measures that are sensitive only to quantum correlations. Here we
study one such measure, namely, entanglement negativity, across finite
temperature phase transitions in several exactly solvable Hamiltonians and find
that it is a singular function of temperature across the transition.<p><a href="http://arxiv.org/abs/1808.04381">read more</a></p>
Wed, 15 Aug 2018 17:04:11 +0200arXiv.org: Quantum Physics: Semiclassical theory of out-of-time-order correlators for low-dimensional classically chaotic systems. (arXiv:1808.04383v1 [quant-ph])
http://arxiv.org/abs/1808.04383
<p>The out-of-time-order correlator (OTOC), recently analyzed in several
physical contexts, is studied for low-dimensional chaotic systems through
semiclassical expansions and numerical simulations. The semiclassical expansion
for the OTOC yields a leading-order contribution in $\hbar^2$ that is
exponentially increasing with time within an intermediate time-window. The
growth-rate in such a regime is governed by the Lyapunov exponent of the
underlying classical system and scales with the square-root of the temperature.
</p>Wed, 15 Aug 2018 17:04:11 +0200arXiv.org: Quantum Physics: Relaxation of Rabi Dynamics in a Superconducting Multiple-Qubit Circuit. (arXiv:1808.04426v1 [quant-ph])
http://arxiv.org/abs/1808.04426
<p>We investigate a superconducting circuit consisting of multiple
capacitively-coupled charge qubits. The collective Rabi oscillation of qubits
is numerically studied in detail by imitating environmental fluctuations
according to the experimental measurement. For the quantum circuit composed of
identical qubits, the energy relaxation of the system strongly depends on the
interqubit coupling strength. As the qubit-qubit interaction is increased, the
system's relaxation rate is enhanced firstly and then significantly reduced.<p><a href="http://arxiv.org/abs/1808.04426">read more</a></p>
Wed, 15 Aug 2018 17:04:11 +0200arXiv.org: Quantum Physics: Investigating nonclassicality in nonlinear electronic spectroscopy. (arXiv:1808.04427v1 [quant-ph])
http://arxiv.org/abs/1808.04427
<p>In this work, we establish a connection between nonlinear electronic
spectroscopy and quantum information protocols for the non-disturbance
condition. The non-fulfillment of the later is a witness of nonclassicality.
Our approach permits us to express the non-disturbance condition in terms of
common observables in the context of electronic spectroscopy experiments, such
as the induced polarization. We then provide the theoretical framework allowing
one to infer nonclassicality from the detected signals in these experiments.<p><a href="http://arxiv.org/abs/1808.04427">read more</a></p>
Wed, 15 Aug 2018 17:04:11 +0200arXiv.org: Quantum Physics: Generating pure single-photon states via spontaneous four-wave mixing in a system of coupled microresonators. (arXiv:1808.04435v1 [quant-ph])
http://arxiv.org/abs/1808.04435
<p>We present the optimal design for an on-chip single-photon source based on
spontaneous four-wave mixing in a system of coupled ring microresonators, which
provides frequency uncorrelated joint spectral amplitude of the biphoton field
and thereby generation of pure single-photon heralded states. A simple method
is proposed for suppressing negative dispersion effects by optimizing the
controlled spectroscopic parameters of the system.<p><a href="http://arxiv.org/abs/1808.04435">read more</a></p>
Wed, 15 Aug 2018 17:04:11 +0200arXiv.org: Quantum Physics: Quantum Algorithms for Autocorrelation Spectrum. (arXiv:1808.04448v1 [quant-ph])
http://arxiv.org/abs/1808.04448
<p>In this paper we design quantum algorithms for studying the autocorrelation
spectrum of a Boolean function and its individual coefficients. Informally, the
autocorrelation coefficient of a Boolean function f() at some point a measures
the average correlation among the values f(x) and f(x xor a). The Walsh
spectrum is a related concept that is well-studied primarily due to its
connection to the quantum circuit for the Deutsch-Jozsa problem but the
autocorrelation spectrum has not received similar attention that we attempt to
deliver in this paper.
</p><p><a href="http://arxiv.org/abs/1808.04448">read more</a></p>
Wed, 15 Aug 2018 17:04:11 +0200arXiv.org: Quantum Physics: Measuring Fermionic Entanglement - Entropy and Negativity. (arXiv:1808.04471v1 [cond-mat.stat-mech])
http://arxiv.org/abs/1808.04471
<p>The recent direct experimental measurement of quantum entanglement paves the
way towards a better understanding of many-body quantum systems and their
correlations. Nevertheless, the overall majority of both the experimental and
theoretical advances had so far been limited to bosonic systems. Here, we study
fermionic systems.<p><a href="http://arxiv.org/abs/1808.04471">read more</a></p>
Wed, 15 Aug 2018 17:04:11 +0200arXiv.org: Quantum Physics: Electromagnetic lattice gauge invariance in two-dimensional discrete-time quantum walks. (arXiv:1808.04488v1 [quant-ph])
http://arxiv.org/abs/1808.04488
<p>Gauge invariance is one of the more important concepts in physics. We discuss
this concept in connection with the unitary evolution of discrete-time quantum
walks in one and two spatial dimensions, when they include the interaction with
synthetic, external electromagnetic fields. One introduces this interaction as
additional phases that play the role of gauge fields. Here, we present a way to
incorporate those phases, which differs from previous works.<p><a href="http://arxiv.org/abs/1808.04488">read more</a></p>
Wed, 15 Aug 2018 17:04:11 +0200