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QUROPE - aggregated feeds in category PhysicsenarXiv.org: Quantum Physics: Impossibility of Cloning of Quantum Coherence. (arXiv:1806.05706v1 [quant-ph])
http://arxiv.org/abs/1806.05706
<p>It is well known that it is impossible to clone an arbitrary quantum state.
However, this inability does not lead directly to no-cloning of quantum
coherence. Here, we show that it is impossible to clone the coherence of an
arbitrary quantum state which is a stronger statement than the 'no-cloning of
quantum state'. In particular, with ancillary system as machine state, we show
that it is impossible to clone the coherence of states whose coherence is
greater than the coherence of the known states on which the transformations are
defined.<p><a href="http://arxiv.org/abs/1806.05706">read more</a></p>
Mon, 18 Jun 2018 11:04:00 +0200arXiv.org: Quantum Physics: Discovering Hamiltonian spectra with variational quantum imaginary time simulation. (arXiv:1806.05707v1 [quant-ph])
http://arxiv.org/abs/1806.05707
<p>Calculating the energy spectrum of a quantum system is an important task, for
example to analyse reaction rates in drug discovery and catalysis. There has
been significant progress in developing algorithms to calculate the ground
state energy of molecules on near-term quantum computers. However, calculating
excited state energies has attracted comparatively less attention, and it is
currently unclear what the optimal method is. We introduce a low depth,
variational quantum algorithm to sequentially calculate the excited states of
general Hamiltonians.<p><a href="http://arxiv.org/abs/1806.05707">read more</a></p>
Mon, 18 Jun 2018 11:04:00 +0200arXiv.org: Quantum Physics: Is there a problem with our Hamiltonians for quantum nonlinear optical processes?. (arXiv:1806.05732v1 [quant-ph])
http://arxiv.org/abs/1806.05732
<p>The models we use, habitually, to describe quantum nonlinear optical
processes have been remarkably successful yet, with few exceptions, they each
contain a mathematical flaw. We present this flaw, show how it can be fixed
and, in the process, suggest why we can continue to use our favoured
Hamiltonians.
</p>Mon, 18 Jun 2018 11:04:00 +0200arXiv.org: Quantum Physics: Probing entanglement entropy via randomized measurements. (arXiv:1806.05747v1 [quant-ph])
http://arxiv.org/abs/1806.05747
<p>Entanglement is the key feature of many-body quantum systems, and the
development of new tools to probe it in the laboratory is an outstanding
challenge. Measuring the entropy of different partitions of a quantum system
provides a way to probe its entanglement structure. Here, we present and
experimentally demonstrate a new protocol for measuring entropy, based on
statistical correlations between randomized measurements.<p><a href="http://arxiv.org/abs/1806.05747">read more</a></p>
Mon, 18 Jun 2018 11:04:00 +0200arXiv.org: Quantum Physics: Schrodinger picture analysis of the beam splitter: an application of the Janszky representation. (arXiv:1806.05748v1 [quant-ph])
http://arxiv.org/abs/1806.05748
<p>The Janszky representation constructs quantum states of a field mode as a
superposition of coherent states on a line in the complex plane. We show that
this provides a natural Schr\"{o}dinger picture description of the interference
between a pair of modes at a beam splitter.
</p>Mon, 18 Jun 2018 11:04:00 +0200arXiv.org: Quantum Physics: Dissipative quantum phase transition of light in a generalized Jaynes-Cummings-Rabi model. (arXiv:1806.05761v1 [quant-ph])
http://arxiv.org/abs/1806.05761
<p>The mean-field steady states of a generalized model of $N$ two-state systems
interacting with one mode of the radiation field in the presence of external
driving and dissipation are surveyed as a function of three control parameters:
one governs the interaction strength relative to the resonance frequency, thus
accessing the Dicke quantum phase transition, a second the relative strength of
counter-rotating to rotating-wave interactions, and a third the amplitude of an
external field driving the cavity mode.<p><a href="http://arxiv.org/abs/1806.05761">read more</a></p>
Mon, 18 Jun 2018 11:04:00 +0200arXiv.org: Quantum Physics: Constrained quantum annealing of graph coloring. (arXiv:1806.05782v1 [quant-ph])
http://arxiv.org/abs/1806.05782
<p>We investigate a quantum annealing approach based on real-time quantum
dynamics for graph coloring. In this approach, a driving Hamiltonian is chosen
so that constraints are naturally satisfied without penalty terms, and the
dimension of the Hilbert space is considerably reduced. The total Hamiltonian,
which consists of driving and problem Hamiltonians, resembles a disordered
quantum spin chain. The ground state of the problem Hamiltonian for graph
coloring is degenerate. This degeneracy is advantageous and is characteristic
of this approach.<p><a href="http://arxiv.org/abs/1806.05782">read more</a></p>
Mon, 18 Jun 2018 11:04:00 +0200arXiv.org: Quantum Physics: Arbitrarily loss-tolerant verification of quantum steering without trustfulness. (arXiv:1806.05807v1 [quant-ph])
http://arxiv.org/abs/1806.05807
<p>We propose a method to verify quantum steering for two qubit states with an
arbitrary amount of null measurement outcomes when both steering and steered
parties cannot be trusted. We modify a score function that it may depend on the
measurement efficiencies of both parties, the number of symmetrically placed
measurement settings, and imperfection of the state preparation. The steering
bound proposed in a recent work [Phys. Rev.<p><a href="http://arxiv.org/abs/1806.05807">read more</a></p>
Mon, 18 Jun 2018 11:04:00 +0200arXiv.org: Quantum Physics: Entanglement-breaking channels with general outcome operator algebras. (arXiv:1806.05854v1 [quant-ph])
http://arxiv.org/abs/1806.05854
<p>A unit-preserving and completely positive linear map, or a channel, $\Lambda
\colon \mathcal{A} \to \mathcal{A}_{\mathrm{in}}$ between $C^\ast$-algebras
$\mathcal{A}$ and $\mathcal{A}_{\mathrm{in}}$ is called entanglement-breaking
(EB) if $\omega \circ( \Lambda \otimes \mathrm{id}_{\mathcal{B}} ) $ is a
separable state for any $C^\ast$-algebra $\mathcal{B}$ and any state $\omega$
on the injective $C^\ast$-tensor product $\mathcal{A}_{\mathrm{in}} \otimes
\mathcal{B} .$ In this paper, we establish the equivalence of the following
conditions for a channel $\Lambda$ with a quantum input space <p><a href="http://arxiv.org/abs/1806.05854">read more</a></p>
Mon, 18 Jun 2018 11:04:00 +0200arXiv.org: Quantum Physics: Synthesizing variable particle interaction potentials via spectrally shaped spatially coherent illumination. (arXiv:1806.05860v1 [quant-ph])
http://arxiv.org/abs/1806.05860
<p>Collective scattering of spatially coherent radiation by separated point
emitters induces inter-particle forces. For particles close to nano-photonic
structures as, for example, nano-fibers, hollow core fibers or photonic
waveguides, this pair-interaction induced by monochromatic light is periodic
and virtually of infinite range. Here we show that the shape and range of the
optical interaction potential can be precisely controlled by spectral design of
the incoming illumination.<p><a href="http://arxiv.org/abs/1806.05860">read more</a></p>
Mon, 18 Jun 2018 11:04:00 +0200