5,755 research outputs found
Majorana Quasi-Particles Protected by Angular Momentum Conservation
We show how angular momentum conservation can stabilise a symmetry-protected
quasi-topological phase of matter supporting Majorana quasi-particles as edge
modes in one-dimensional cold atom gases. We investigate a number-conserving
four-species Hubbard model in the presence of spin-orbit coupling. The latter
reduces the global spin symmetry to an angular momentum parity symmetry, which
provides an extremely robust protection mechanism that does not rely on any
coupling to additional reservoirs. The emergence of Majorana edge modes is
elucidated using field theory techniques, and corroborated by
density-matrix-renormalization-group simulations. Our results pave the way
toward the observation of Majorana edge modes with alkaline-earth-like fermions
in optical lattices, where all basic ingredients for our recipe - spin-orbit
coupling and strong inter-orbital interactions - have been experimentally
realized over the last two years.Comment: 12 pages (6 + 6 supplementary material
Wilson Fermions and Axion Electrodynamics in Optical Lattices
The formulation of massless relativistic fermions in lattice gauge theories
is hampered by the fundamental problem of species doubling, namely, the rise of
spurious fermions modifying the underlying physics. A suitable tailoring of the
fermion masses prevents such abundance of species, and leads to the so-called
Wilson fermions. Here we show that ultracold atoms provide us with the first
controllable realization of these paradigmatic fermions, thus generating a
quantum simulator of fermionic lattice gauge theories. We describe a novel
scheme that exploits laser-assisted tunneling in a cubic optical superlattice
to design the Wilson fermion masses. The high versatility of this proposal
allows us to explore a variety of interesting phases in three-dimensional
topological insulators, and to test the remarkable predictions of axion
electrodynamics.Comment: RevTex4 file, color figures, slightly longer than the published
versio
Emerging Bosons with Three-Body Interactions from Spin-1 Atoms in Optical Lattices
We study two many-body systems of bosons interacting via an infinite
three-body contact repulsion in a lattice: a pairs quasi-condensate induced by
correlated hopping and the discrete version of the Pfaffian wavefunction. We
propose to experimentally realise systems characterized by such interaction by
means of a proper spin-1 lattice Hamiltonian: spin degrees of freedom are
locally mapped into occupation numbers of emerging bosons, in a fashion similar
to spin-1/2 and hardcore bosons. Such a system can be realized with ultracold
spin-1 atoms in a Mott Insulator with filling-factor one. The high versatility
of these setups allows us to engineer spin-hopping operators breaking the SU(2)
symmetry, as needed to approximate interesting bosonic Hamiltonians with
three-body hardcore constraint. For this purpose we combine bichromatic
spin-independent superlattices and Raman transitions to induce a different
hopping rate for each spin orientation. Finally, we illustrate how our setup
could be used to experimentally realize the first setup, i.e. the transition to
a pairs quasi-condensed phase of the emerging bosons. We also report on a route
towards the realization of a discrete bosonic Pfaffian wavefunction and list
some open problems to reach this goal.Comment: 17 pages, 13 figure
Entropy-driven enhanced self-diffusion in confined reentrant supernematics
We present a molecular dynamics study of reentrant nematic phases using the
Gay-Berne-Kihara model of a liquid crystal in nanoconfinement. At densities
above those characteristic of smectic A phases, reentrant nematic phases form
that are characterized by a large value of the nematic order parameter
. Along the nematic director these "supernematic" phases exhibit a
remarkably high self-diffusivity which exceeds that for ordinary, lower-density
nematic phases by an order of magnitude. Enhancement of self-diffusivity is
attributed to a decrease of rotational configurational entropy in confinement.
Recent developments in the pulsed field gradient NMR technique are shown to
provide favorable conditions for an experimental confirmation of our
simulations.Comment: 10 pages, 5 figure
Topological Wilson-loop area law manifested using a superposition of loops
We introduce a new topological effect involving interference of two meson
loops, manifesting a path-independent topological area dependence. The effect
also draws a connection between quark confinement, Wilson-loops and topological
interference effects. Although this is only a gedanken experiment in the
context of particle physics, such an experiment may be realized and used as a
tool to test confinement effects and phase transitions in quantum simulation of
dynamic gauge theories.Comment: Superceding arXiv:1206.2021v1 [quant-ph
Anthocyanin and aroma profiling of the 'Albarossa' grapevine crossbreed (Vitis vinifera L.) and its parent varieties 'Barbera' and 'Nebbiolo di Dronero'
V. vinifera L. 'Barbera', 'Nebbiolo di Dronero' and the crossbreed 'Albarossa', grown in Piedmont region, Italy, were characterized by the analysis of grape anthocyanins, using High Performance Liquid Chromatography (HPLC), and aromatic compounds using Gas Chromatography coupled with Mass Spectrometry (GC-MS). Five monomeric non-acylated anthocyanins, delphinidin-3-monoglucoside, cyanidin-3-monoglucoside, petunidin-3-monoglucoside, peonidin-3-monoglucoside, malvidin-3-monoglucoside, and the pool of acetic acid acylated anthocyanins and coumarate/caffeoate anthocyanins were detected, as well as the concentration of terpenes, norisoprenoids, alcohols and benzene compounds. Ratios between the different anthocyanin forms were used for varietal profiling, as well as ratios and concentrations of single or pooled aromatic compounds. 'Albarossa' had intermediate levels, between 'Barbera' and 'Nebbiolo di Dronero', of certain anthocyanins and aromas, due to the genetic relationships.
 
Field-Driven Mott Gap Collapse and Resistive Switch in Correlated Insulators
Mott insulators are "unsuccessful metals" in which Coulomb repulsion prevents charge conduction despite a metal-like concentration of conduction electrons. The possibility to unlock the frozen carriers with an electric field offers tantalizing prospects of realizing new Mott-based microelectronic devices. Here we unveil how such unlocking happens in a simple model that shows the coexistence of a stable Mott insulator and a metastable metal. Considering a slab subject to a linear potential drop, we find, by means of the dynamical mean-field theory, that the electric breakdown of the Mott insulator occurs via a first-order insulator-to-metal transition characterized by an abrupt gap collapse in sharp contrast to the standard Zener breakdown. The switch on of conduction is due to the field-driven stabilization of the metastable metallic phase. Outside the region of insulator-metal coexistence, the electric breakdown occurs through a more conventional quantum tunneling across the Hubbard bands tilted by the field. Our findings rationalize recent experimental observations and may offer a guideline for future technological research
Robustness of quantum memories based on Majorana zero modes
We analyze the rate at which quantum information encoded in zero-energy Majorana modes is lost in the presence of perturbations. We show that information can survive for times that scale exponentially with the size of the chain both in the presence of quenching and time-dependent quadratic dephasing perturbations, even when the latter have spectral components above the system's energy gap. The origin of the robust storage, namely the fact that a sudden quench affects in the same way both parity sectors of the original spectrum, is discussed, together with the memory performance at finite temperatures and in the presence of particle exchange with a bath.Physic
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