42 research outputs found
Topological Entanglement Entropy of a Bose-Hubbard Spin Liquid
The Landau paradigm of classifying phases by broken symmetries was
demonstrated to be incomplete when it was realized that different quantum Hall
states could only be distinguished by more subtle, topological properties.
Today, the role of topology as an underlying description of order has branched
out to include topological band insulators, and certain featureless gapped Mott
insulators with a topological degeneracy in the groundstate wavefunction.
Despite intense focus, very few candidates for these topologically ordered
"spin liquids" exist. The main difficulty in finding systems that harbour spin
liquid states is the very fact that they violate the Landau paradigm, making
conventional order parameters non-existent. Here, we uncover a spin liquid
phase in a Bose-Hubbard model on the kagome lattice, and measure its
topological order directly via the topological entanglement entropy. This is
the first smoking-gun demonstration of a non-trivial spin liquid, identified
through its entanglement entropy as a gapped groundstate with emergent Z2 gauge
symmetry.Comment: 4+ pages, 3 figure
Construction et classification de certaines solutions algébriques des systèmes de Garnier
22 pagesInternational audienceIn this paper, we classify all (complete) non elementary algebraic solutions of Garnier systems that can be constructed by Kitaev's method: they are deduced from isomonodromic deformations defined by pulling back a given fuchsian equation E by a family of ramified covers. We first introduce orbifold structures associated to a fuchsian equation. This allow to get a refined version of Riemann-Hurwitz formula and then to promtly deduce that E is hypergeometric. Then, we can bound exponents and degree of the pull-back maps and further list all possible ramification cases. This generalizes a result due to C. Doran for the Painleve VI case. We explicitely construct one of these solutions
A Rydberg Quantum Simulator
Following Feynman and as elaborated on by Lloyd, a universal quantum
simulator (QS) is a controlled quantum device which reproduces the dynamics of
any other many particle quantum system with short range interactions. This
dynamics can refer to both coherent Hamiltonian and dissipative open system
evolution. We investigate how laser excited Rydberg atoms in large spacing
optical or magnetic lattices can provide an efficient implementation of a
universal QS for spin models involving (high order) n-body interactions. This
includes the simulation of Hamiltonians of exotic spin models involving
n-particle constraints such as the Kitaev toric code, color code, and lattice
gauge theories with spin liquid phases. In addition, it provides the
ingredients for dissipative preparation of entangled states based on
engineering n-particle reservoir couplings. The key basic building blocks of
our architecture are efficient and high-fidelity n-qubit entangling gates via
auxiliary Rydberg atoms, including a possible dissipative time step via optical
pumping. This allows to mimic the time evolution of the system by a sequence of
fast, parallel and high-fidelity n-particle coherent and dissipative Rydberg
gates.Comment: 8 pages, 4 figure
Evidence of Majorana fermions in an Al - InAs nanowire topological superconductor
Majorana fermions are the only fermionic particles that are expected to be
their own antiparticles. While elementary particles of the Majorana type were
not identified yet, quasi-particles with Majorana like properties, born from
interacting electrons in the solid, were predicted to exist. Here, we present
thorough experimental studies, backed by numerical simulations, of a system
composed of an aluminum superconductor in proximity to an indium arsenide
nanowire, with the latter possessing strong spin-orbit coupling. An induced 1d
topological superconductor - supporting Majorana fermions at both ends - is
expected to form. We concentrate on the characteristics of a distinct zero bias
conductance peak (ZBP), and its splitting in energy, both appearing only with a
small magnetic field applied along the wire. The ZBP was found to be robustly
tied to the Fermi energy over a wide range of system parameters. While not
providing a definite proof of a Majorana state, the presented data and the
simulations support strongly its existence
Topologically Protected Quantum State Transfer in a Chiral Spin Liquid
Topology plays a central role in ensuring the robustness of a wide variety of
physical phenomena. Notable examples range from the robust current carrying
edge states associated with the quantum Hall and the quantum spin Hall effects
to proposals involving topologically protected quantum memory and quantum logic
operations. Here, we propose and analyze a topologically protected channel for
the transfer of quantum states between remote quantum nodes. In our approach,
state transfer is mediated by the edge mode of a chiral spin liquid. We
demonstrate that the proposed method is intrinsically robust to realistic
imperfections associated with disorder and decoherence. Possible experimental
implementations and applications to the detection and characterization of spin
liquid phases are discussed.Comment: 14 pages, 7 figure
Quantum magnetism and criticality
Magnetic insulators have proved to be fertile ground for studying new types
of quantum many body states, and I survey recent experimental and theoretical
examples. The insights and methods transfer also to novel superconducting and
metallic states. Of particular interest are critical quantum states, sometimes
found at quantum phase transitions, which have gapless excitations with no
particle- or wave-like interpretation, and control a significant portion of the
finite temperature phase diagram. Remarkably, their theory is connected to
holographic descriptions of Hawking radiation from black holes.Comment: 39 pages, 10 figures, review article for non-specialists; (v2) added
clarifications and references; (v3) minor corrections; (v4) added footnote on
hydrodynamic long-time tail
Topological Photonics
Topology is revolutionizing photonics, bringing with it new theoretical
discoveries and a wealth of potential applications. This field was inspired by
the discovery of topological insulators, in which interfacial electrons
transport without dissipation even in the presence of impurities. Similarly,
new optical mirrors of different wave-vector space topologies have been
constructed to support new states of light propagating at their interfaces.
These novel waveguides allow light to flow around large imperfections without
back-reflection. The present review explains the underlying principles and
highlights the major findings in photonic crystals, coupled resonators,
metamaterials and quasicrystals.Comment: progress and review of an emerging field, 12 pages, 6 figures and 1
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MBST-exposure opportunities as a monotherapy of chronic dorsalgia
The aim: to analyze the clinical effect of MBST-exposure monotherapy, a magnetic resonance method, on the pain syndrome caused by degenerative dystrophic changes of vertebral column structures. Material and Methods. 132 patients both male and female with cervical and lumbar dorsopathy were enrolled into the study. Treatment course included 9 sessions of 60 min. daily. MRI-results of corresponding spine regions and visual analogue pain intensity scale were used as assessment tools for treatment efficiency before, immediately after, 3, 6 and 12 months after MBST-treatment. Results. The objective results of structural transformation of pathological formations in vertebral motional segments correlated with significant decrease of pain syndrome at all stages of control tests. Conclusion. MBST-exposure is an effective method of non-invasive, notouch monotherapy for patients with chronic dorsalgia caused by degenerative dorsopathy.</p