1,930 research outputs found
Robust zero-energy modes in an electronic higher-order topological insulator: the dimerized Kagome lattice
Quantum simulators are an essential tool for understanding complex quantum
materials. Platforms based on ultracold atoms in optical lattices and photonic
devices led the field so far, but electronic quantum simulators are proving to
be equally relevant. Simulating topological states of matter is one of the holy
grails in the field. Here, we experimentally realize a higher-order electronic
topological insulator (HOTI). Specifically, we create a dimerized Kagome
lattice by manipulating carbon-monoxide (CO) molecules on a Cu(111) surface
using a scanning tunneling microscope (STM). We engineer alternating weak and
strong bonds to show that a topological state emerges at the corner of the
non-trivial configuration, while it is absent in the trivial one. Contrarily to
conventional topological insulators (TIs), the topological state has two
dimensions less than the bulk, denoting a HOTI. The corner mode is protected by
a generalized chiral symmetry, which leads to a particular robustness against
perturbations. Our versatile approach to quantum simulation with artificial
lattices holds promises of revealing unexpected quantum phases of matter
Comment on "Control landscapes are almost always trap free: a geometric assessment"
We analyze a recent claim that almost all closed, finite dimensional quantum
systems have trap-free (i.e., free from local optima) landscapes (B. Russell
et.al. J. Phys. A: Math. Theor. 50, 205302 (2017)). We point out several errors
in the proof which compromise the authors' conclusion.
Interested readers are highly encouraged to take a look at the "rebuttal"
(see Ref. [1]) of this comment published by the authors of the criticized work.
This "rebuttal" is a showcase of the way the erroneous and misleading
statements under discussion will be wrapped up and injected in their future
works, such as R. L. Kosut et.al, arXiv:1810.04362 [quant-ph] (2018).Comment: 6 pages, 1 figur
Frozen and Invariant Quantum Discord under Local Dephasing Noise
In this chapter, we intend to explore and review some remarkable dynamical
properties of quantum discord under various different open quantum system
models. Specifically, our discussion will include several concepts connected to
the phenomena of time invariant and frozen quantum discord. Furthermore, we
will elaborate on the relation of these two phenomena to the non-Markovian
features of the open system dynamics and to the usage of dynamical decoupling
protocols.Comment: 29 pages, 8 figure
Evolutionary Approaches to Optimization Problems in Chimera Topologies
Chimera graphs define the topology of one of the first commercially available
quantum computers. A variety of optimization problems have been mapped to this
topology to evaluate the behavior of quantum enhanced optimization heuristics
in relation to other optimizers, being able to efficiently solve problems
classically to use them as benchmarks for quantum machines. In this paper we
investigate for the first time the use of Evolutionary Algorithms (EAs) on
Ising spin glass instances defined on the Chimera topology. Three genetic
algorithms (GAs) and three estimation of distribution algorithms (EDAs) are
evaluated over hard instances of the Ising spin glass constructed from
Sidon sets. We focus on determining whether the information about the topology
of the graph can be used to improve the results of EAs and on identifying the
characteristics of the Ising instances that influence the success rate of GAs
and EDAs.Comment: 8 pages, 5 figures, 3 table
Device-Independent Bit Commitment based on the CHSH Inequality
Bit commitment and coin flipping occupy a unique place in the
device-independent landscape, as the only device-independent protocols thus far
suggested for these tasks are reliant on tripartite GHZ correlations. Indeed,
we know of no other bipartite tasks, which admit a device-independent
formulation, but which are not known to be implementable using only bipartite
nonlocality. Another interesting feature of these protocols is that the
pseudo-telepathic nature of GHZ correlations -- in contrast to the generally
statistical character of nonlocal correlations, such as those arising in the
violation of the CHSH inequality -- is essential to their formulation and
analysis. In this work, we present a device-independent bit commitment protocol
based on CHSH testing, which achieves the same security as the optimal
GHZ-based protocol. The protocol is analyzed in the most general settings,
where the devices are used repeatedly and may have long-term quantum memory. We
also recast the protocol in a post-quantum setting where both honest and
dishonest parties are restricted only by the impossibility of signaling, and
find that overall the supra-quantum structure allows for greater security.Comment: 15 pages, 3 figure
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