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QUROPE - aggregated feedsenarXiv.org: Quantum Physics: On the Theory of Modern Quantum Algorithms. (arXiv:2009.10088v1 [quant-ph])
http://arxiv.org/abs/2009.10088
<p>This dissertation unites variational computation with results and techniques
appearing in the theory of ground state computation. It should be readable by
graduate students.
</p>
<p>The topics covered include: Ising model reductions, stochastic versus quantum
processes on graphs, quantum gates and circuits as tensor networks, variational
quantum algorithms and Hamiltonian gadgets.
</p>Wed, 23 Sep 2020 23:51:38 +0200arXiv.org: Quantum Physics: Optimal environment localization. (arXiv:2009.10094v1 [quant-ph])
http://arxiv.org/abs/2009.10094
<p>Quantum channels model many physical processes. For this reason, hypothesis
testing between quantum channels is a fundamental task in quantum information
theory. Here we consider the paradigmatic case of channel position finding,
where the aim is to determine the position of a target quantum channel within a
sequence of background channels. We explore this model in the setting of
bosonic systems, considering Gaussian channels with the same transmissivity (or
gain) but different levels of environmental noise.<p><a href="http://arxiv.org/abs/2009.10094">read more</a></p>
Wed, 23 Sep 2020 23:51:38 +0200arXiv.org: Quantum Physics: Warm-starting quantum optimization. (arXiv:2009.10095v1 [quant-ph])
http://arxiv.org/abs/2009.10095
<p>There is an increasing interest in quantum algorithms for problems of
combinatorial optimization. Classical solvers for such problems employ
relaxations, which replace binary variables with continuous ones, for instance
in the form of higher-dimensional matrix-valued problems (semidefinite
programming).<p><a href="http://arxiv.org/abs/2009.10095">read more</a></p>
Wed, 23 Sep 2020 23:51:38 +0200arXiv.org: Quantum Physics: Dielectric loss in epitaxial Al/GaAs/Al trilayers for superconducting circuits. (arXiv:2009.10101v1 [physics.app-ph])
http://arxiv.org/abs/2009.10101
<p>Epitaxially-grown superconductor/dielectric/superconductor trilayers have the
potential to form high-performance superconducting quantum devices and may even
allow scalable superconducting quantum computing with low-surface-area qubits
such as the merged-element transmon. In this work, we measure the
power-independent loss and two-level-state (TLS) loss of epitaxial,
wafer-bonded, and substrate-removed Al/GaAs/Al trilayers by measuring lumped
element superconducting microwave resonators at millikelvin temperatures and
down to single photon powers.<p><a href="http://arxiv.org/abs/2009.10101">read more</a></p>
Wed, 23 Sep 2020 23:51:38 +0200arXiv.org: Quantum Physics: Scrambling and Lyapunov Exponent in Unitary Networks with Tunable Interactions. (arXiv:2009.10104v1 [cond-mat.str-el])
http://arxiv.org/abs/2009.10104
<p>Scrambling of information in a quantum many-body system, quantified by the
out-of-time-ordered correlator (OTOC), is a key manifestation of quantum chaos.
A regime of exponential growth in the OTOC, characterized by a Lyapunov
exponent, has so far mostly been observed in systems with a high-dimensional
local Hilbert space and in weakly-coupled systems. Here, we propose a general
criterion for the existence of a well-defined regime of exponential growth of
the OTOC in spatially extended systems with local interactions.<p><a href="http://arxiv.org/abs/2009.10104">read more</a></p>
Wed, 23 Sep 2020 23:51:38 +0200arXiv.org: Quantum Physics: Influence matrix approach to many-body Floquet dynamics. (arXiv:2009.10105v1 [cond-mat.str-el])
http://arxiv.org/abs/2009.10105
<p>In this work, we introduce an approach to study quantum many-body dynamics,
inspired by the Feynman-Vernon influence functional. Focusing on a family of
interacting, Floquet spin chains, we consider a Keldysh path-integral
description of the dynamics. The central object in our approach is the
influence matrix (IM), which describes the effect of the system on the dynamics
of a local subsystem. For translationally invariant models, we formulate a
self-consistency equation for the influence matrix.<p><a href="http://arxiv.org/abs/2009.10105">read more</a></p>
Wed, 23 Sep 2020 23:51:38 +0200arXiv.org: Quantum Physics: Polynomial growth of out-of-time-order correlator in arbitrary realistic long-range interacting systems. (arXiv:2009.10124v1 [quant-ph])
http://arxiv.org/abs/2009.10124
<p>In this study, we investigate out-of-time-order correlators (OTOCs) in
systems with power-law decaying interactions such as $R^{-\alpha}$, where $R$
is the distance. In such systems, the fast scrambling of quantum information or
the exponential growth of information propagation can occur according to the
decay rate $\alpha$. In this regard, it has been an intriguing open question to
identify the critical $\alpha_c$ above which fast scrambling cannot occur.<p><a href="http://arxiv.org/abs/2009.10124">read more</a></p>
Wed, 23 Sep 2020 23:51:38 +0200arXiv.org: Quantum Physics: TIGER: Topology-aware Assignment using Ising machines Application to Classical Algorithm Tasks and Quantum Circuit Gates. (arXiv:2009.10151v1 [cs.ET])
http://arxiv.org/abs/2009.10151
<p>Optimally mapping a parallel application to compute and communication
resources is increasingly important as both system size and heterogeneity
increase. A similar mapping problem exists in gate-based quantum computing
where the objective is to map tasks to gates in a topology-aware fashion. This
is an NP-complete graph isomorphism problem, and existing task assignment
approaches are either heuristic or based on physical optimization algorithms,
providing different speed and solution quality trade-offs.<p><a href="http://arxiv.org/abs/2009.10151">read more</a></p>
Wed, 23 Sep 2020 23:51:38 +0200arXiv.org: Quantum Physics: Superstripes and quasicrystals in bosonic systems with hard-soft corona interactions. (arXiv:2009.10203v1 [cond-mat.quant-gas])
http://arxiv.org/abs/2009.10203
<p>The search for spontaneous pattern formation in equilibrium phases with
genuine quantum properties is a leading direction of current research. In this
work we investigate the effect of quantum fluctuations - zero point motion and
exchange interactions - on the phases of an ensemble of bosonic particles with
isotropic hard-soft corona interactions. We perform extensive path-integral
Monte Carlo simulations to determine their ground state properties.<p><a href="http://arxiv.org/abs/2009.10203">read more</a></p>
Wed, 23 Sep 2020 23:51:38 +0200arXiv.org: Quantum Physics: Parity-time symmetric systems with memory. (arXiv:2009.10211v1 [quant-ph])
http://arxiv.org/abs/2009.10211
<p>Classical open systems with balanced gain and loss, i.e. parity-time
($\mathcal{PT}$) symmetric systems, have attracted tremendous attention over
the past decade. Their exotic properties arise from exceptional point (EP)
degeneracies of non-Hermitian Hamiltonians that govern their dynamics.<p><a href="http://arxiv.org/abs/2009.10211">read more</a></p>
Wed, 23 Sep 2020 23:51:38 +0200