Reentrant topological transitions with Majorana end states in 1D superconductors by lattice modulation

The possibility to observe and manipulate Majorana fermions as end states of one-dimensional topological superconductors has been actively discussed recently. In a quantum wire with strong spin-orbit coupling placed in proximity to a bulk superconductor, a topological superconductor has been expected to be realized when the band energy is split by the application of a magnetic field. When a periodic lattice modulation is applied multiple topological superconductor phases appear in the phase diagram. Some of them occur for higher filling factors compared to the case without the modulation. We study the effects of phase jumps and argue that the topologically nontrivial state of the whole system is retained even if they are present. We also study the effect of the spatial modulation in the hopping parameter.Comment: 10 pages, 9 figures, submitted to Phys. Rev.

Reentrant topological transitions in a quantum wire/superconductor system with quasiperiodic lattice modulation

We study the condition for a topological superconductor (TS) phase with end Majorana fermions to appear when a quasiperiodic lattice modulation is applied to a one-dimensional quantum wire with strong spin-orbit interaction situated under a magnetic field and in proximity to a superconductor. By density-matrix renormalization group analysis, we find that multiple topological phases with Majorana end modes are realized in finite ranges of the filling factor, showing a sequence of reentrant transitions as the chemical potential is tuned. The locations of these phases reflect the structure of bands in the non-interacting case, which exhibits a distinct self-similar structure. The stability of the TS in the presence of an on-site interaction or a harmonic trap potential is also discussed.Comment: 5 pages, 4 figures, v4: minor corrections; published in Phys. Rev. B Rapid Communicatio

Drag dynamics in one-dimensional Fermi systems

We study drag dynamics of several fermions in a fermion cloud in one-dimensional continuous systems, with particular emphasis on the non-trivial quantum many-body effects in systems whose parameters change gradually in real time. We adopt the Fermi--Hubbard model and the time-dependent density matrix renormalization group method to calculate the drag force on a trapped fermion cluster in a cloud of another fermion species with contact interaction. The simulation result shows that a non-trivial peak in the resistance force is observed in the high cloud density region, which implies a criterion of effective ways in diffusive transport in a fermion cloud. We compare the DMRG simulation result with a mean-field result, and it is suggested that some internal degrees of freedom have a crucial role in the excitation process when the cloud density is high. This work emphasizes the difference between the full-quantum calculation and the semiclassical calculation, which is the quantum effects, in slow dynamics of many-body systems bound in a fermion cloud.Comment: 7 pages, 8 figure

Density-Matrix Renormalization Group Study of Trapped Imbalanced Fermi Condensates

The density-matrix renormalization group is employed to investigate a harmonically-trapped imbalanced Fermi condensate based on a one-dimensional attractive Hubbard model. The obtained density profile shows a flattened population difference of spin-up and spin-down components at the center of the trap, and exhibits phase separation between the condensate and unpaired majority atoms for a certain range of the interaction and population imabalance $P$. The two-particle density matrix reveals that the sign of the order parameter changes periodically, demonstrating the realization of the Fulde-Ferrell-Larkin-Ovchinnikov phase. The minority spin atoms contribute to the quasi-condensate up to at least $P \simeq 0.8$. Possible experimental situations to test our predictions are discussed.Comment: 4 pages, 3 figures; added references; accepted for publication in Phys. Rev. Let

Disposable collection kit for rapid and reliable collection of saliva.

ObjectivesTo describe and evaluate disposable saliva collection kit for rapid, reliable, and reproducible collection of saliva samples.MethodsThe saliva collection kit comprised of a saliva absorbent swab and an extractor unit was used to retrieve whole saliva samples from 10 subjects. The accuracy and precision of the extracted volumes (3, 10, and 30 μl) were compared to similar volumes drawn from control samples obtained by passive drool. Additionally, the impact of kit collection method on subsequent immunoassay results was verified by assessing salivary cortisol levels in the samples and comparing them to controls.ResultsThe recovered volumes for the whole saliva samples were 3.85 ± 0.28, 10.79 ± 0.95, and 31.18 ± 1.72 μl, respectively (CV = 8.76%) and 2.91 ± 0.19, 9.75 ± 0.43, and 29.64 ± 0.91 μl, respectively, (CV = 6.36%) for the controls. There was a close correspondence between the salivary cortisol levels from the saliva samples obtained by the collection kit and the controls (R(2)  > 0.96).ConclusionsThe disposable saliva collection kit allows accurate and repeatable collection of fixed amounts of whole saliva and does not interfere with subsequent measurements of salivary cortisol. The simple collection process, lack of elaborate specimen recovery steps, and the short turnaround time (<3 min) should render the kit attractive to test subjects and researchers alike