49 research outputs found
Topologically protected quantization of work
The transport of a particle in the presence of a potential that changes
periodically in space and in time can be characterized by the amount of work
needed to shift a particle by a single spatial period of the potential. In
general, this amount of work, when averaged over a single temporal period of
the potential, can take any value in a continuous fashion. Here we present a
topological effect inducing the quantization of the average work. We find that
this work is equal to the first Chern number calculated in a unit cell of a
space-time lattice. Hence, this quantization of the average work is
topologically protected. We illustrate this phenomenon with the example of an
atom whose center of mass motion is coupled to its internal degrees of freedom
by electromagnetic waves.Comment: 10 pages (including Supplemental Material), 1 figure, 1 table; closer
to published versio
A theorem regarding families of topologically non-trivial fermionic systems
We introduce a Hamiltonian for fermions on a lattice and prove a theorem
regarding its topological properties. We identify the topological criterion as
a topological invariant (the Pfaffian
polynomial). The topological invariant is not only the first Chern number, but
also the sign of the Pfaffian polynomial coming from a notion of duality. Such
Hamiltonian can describe non-trivial Chern insulators, single band
superconductors or multiorbital superconductors. The topological features of
these families are completely determined as a consequence of our theorem. Some
specific model examples are explicitly worked out, with the computation of
different possible topological invariants.Comment: 6 page
Nontrivial quantum geometry of degenerate flat bands
The importance of the quantum metric in flat-band systems has been noticed
recently in many contexts such as the superfluid stiffness, the dc electrical
conductivity, and ideal Chern insulators. Both the quantum metric of degenerate
and nondegenerate bands can be naturally described via the geometry of
different Grassmannian manifolds, specific to the band degeneracies. Contrary
to the (Abelian) Berry curvature, the quantum metric of a degenerate band
resulting from the collapse of a collection of bands is not simply the sum of
the individual quantum metrics. We provide a physical interpretation of this
phenomenon in terms of transition dipole matrix elements between two bands. By
considering a toy model, we show that the quantum metric gets enhanced,
reduced, or remains unaffected depending on which bands collapse. The dc
longitudinal conductivity and the superfluid stiffness are known to be
proportional to the quantum metric for flat-band systems, which makes them
suitable candidates for the observation of this phenomenon.Comment: 6+15 pages (including Supplemental Material), 2+2 figures; closer to
published versio
Dynamical phase transitions at finite temperature from fidelity and interferometric Loschmidt echo induced metrics
We study finite-temperature Dynamical Quantum Phase Transitions (DQPTs) by
means of the fidelity and the interferometric Loschmidt Echo (LE) induced
metrics. We analyse the associated dynamical susceptibilities (Riemannian
metrics), and derive analytic expressions for the case of two-band
Hamiltonians. At zero temperature the two quantities are identical,
nevertheless, at finite temperatures they behave very differently. Using the
fidelity LE, the zero temperature DQPTs are gradually washed away with
temperature, while the interferometric counterpart exhibits finite-temperature
Phase Transitions (PTs). We analyse the physical differences between the two
finite-temperature LE generalisations, and argue that, while the
interferometric one is more sensitive and can therefore provide more
information when applied to genuine quantum (microscopic) systems, when
analysing many-body macroscopic systems, the fidelity-based counterpart is a
more suitable quantity to study. Finally, we apply the previous results to two
representative models of topological insulators in 1D and 2D.Comment: 20 pages, 8 figure
High purity galacto-oligosaccharides enhance specific Bifidobacterium species and their metabolic activity in the mouse gut microbiome
Prebiotics are selectively fermented ingredients that result in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefit(s) upon the host health. The aim of this study was to evaluate the influence of a β (1–4) galacto-oligosaccharides formulation consisting of 90% pure GOS (GOS90), on the composition and activity of the mouse gut microbiota. Germ-free mice were colonized with microbiota from four pathogen-free wt 129 mice donors (SPF), and stools were collected during a feeding trial in which GOS90 was delivered orally for 14 days. Pyrosequencing of 16S rDNA amplicons showed that Bifidobacterium and specific Lactobacillus, Bacteroides and Clostridiales were more prevalent in GOS90-fed mice after 14 days, although the prebiotic impact on Bifidobacterium varied among individual mice. Prebiotic feeding also resulted in decreased abundance of Bacteroidales, Helicobacter and Clostridium. High-throughput quantitative PCR showed an increased abundance of Bifidobacterium adolescentis, B. pseudocatenulatum, B. lactis and B. gallicum in the prebiotic-fed mice. Control female mice showed a higher diversity (Phylogenetic Diversity PD = 15.1 ± 3.4 in stools and PD = 13.0 ± 0.6 in intestinal contents) than control males (PD = 7.8 ± 1.6 in stool samples and PD = 9.5 ± 1.0 in intestinal contents). GOS90 did not modify inflammatory biomarkers (IL-6, IL-12, IL-1β, IFN-γ and TNF-α). Decreased butyrate, acetate and lactate concentrations in stools of prebiotic fed mice suggested an increase in colonic absorption and reduced excretion. Overall, our results demonstrate that GOS90 is capable of modulating the intestinal microbiome resulting in expansion of the probiome (autochtonous commensal intestinal bacteria considered to have a beneficial influence on health)