Lifetime of Majorana qubits in Rashba nanowires with non-uniform chemical potential

We study the lifetime of topological qubits based on Majorana bound states hosted in a one-dimensional Rashba nanowire (NW) with proximity-induced superconductivity and non-uniform chemical potential needed for manipulation and read-out. If nearby gates tune the chemical potential locally so that part of the NW is in the trivial phase, Andreev bound states (ABSs) can emerge which are localized at the interface between topological and trivial phases with energies significantly less than the gap. The emergence of such subgap states strongly decreases the Majorana qubit lifetime at finite temperatures due to local perturbations that can excite the system into these ABSs. Using Keldysh formalism, we study such excitations caused by fluctuating charges in capacitively coupled gates and calculate the corresponding Majorana lifetimes due to thermal noise, which are shown to be much shorter than those in NWs with uniform chemical potential.Comment: 9 pages, 8 figure

Degeneracy lifting of Majorana bound states due to electron-phonon interactions

We study theoretically how electron-phonon interaction affects the energies and level broadening (inverse lifetime) of Majorana bound states (MBSs) in a clean topological nanowire at low temperatures. At zero temperature, the energy splitting between the right and left MBSs remains exponentially small with increasing nanowire length $L$. At finite temperatures, however, the absorption of thermal phonons leads to the broadening of energy levels of the MBSs that does not decay with system length, and the coherent absorption/emission of phonons at opposite ends of the nanowire results in MBSs energy splitting that decays only as an inverse power-law in $L$. Both effects remain exponential in temperature. In the case of quantized transverse motion of phonons, the presence of Van Hove singularities in the phonon density of states causes additional resonant enhancement of both the energy splitting and the level broadening of the MBSs. This is the most favorable case to observe the phonon-induced energy splitting of MBSs as it becomes much larger than the broadening even if the topological nanowire is much longer than the coherence length. We also calculate the charge and spin associated with the energy splitting of the MBSs induced by phonons. We consider both a spinless low-energy continuum model, which we evaluate analytically, as well as a spinful lattice model for a Rashba nanowire, which we evaluate numerically

Heavy-Ion Beam Acceleration of Two-Charge States from an Ecr Ion Source

This paper describes a design for the front end of a superconducting (SC) ion linac which can accept and simultaneously accelerate two charge states of uranium from an ECR ion source. This mode of operation increases the beam current available for the heaviest ions by a factor of two. We discuss the 12 MeV/u prestripper section of the Rare Isotope Accelerator (RIA) driver linac including the LEBT, RFQ, MEBT and SC sections, with a total voltage of 112 MV. The LEBT consists of two bunchers and electrostatic quadrupoles. The fundamental frequency of both bunchers is half of the RFQ frequency. The first buncher is a multiharmonic buncher, designed to accept more than 80% of each charge state and to form bunches of extremely low longitudinal emittance (rms emittance is lower than 0.2 keV/u nsec) at the output of the RFQ. The second buncher is located directly in front of the RFQ and matches the velocity of each charge-state bunch to the design input velocity of the RFQ. We present full 3D simulations of a two-charge-state uranium beam including space charge forces in the LEBT and RFQ, realistic distributions of all electric and magnetic fields along the whole prestripper linac, and the effects of errors, evaluated for several design options for the prestripper linac. The results indicate that it is possible to accelerate two charge states while keeping emittance growth within tolerable limits.Comment: LINAC2000, MOD0

Reduction in ionic permeability of a silicone hydrogel contact lenses after one month of daily wear

[EN] Purpose. To compare the ionic permeability using the ionoflux method of new and worn samples of a silicone hydrogel contact lens material. Methods. An ionoflux experimental setup was established to measure the ionic permeability (NaCl) of soft contact lenses. Samples of a silicone hydrogel lens (Comfilcon A, Coopervision, Pleasanton, CA) with optical powers of -1.00, -1.50 and -4.75 diopters (D) were used in this study. Three samples of each power were measured after being worn for one month on a daily wear basis. Lenses were cleaned and disinfected every night using multipurpose disinfecting solutions. Three samples of new lenses from the same batch and the same optical power were also measured to evaluate the effect of lens wear on the ionic permeability of the lens material. Before measurement, the lenses were equilibrated with a 1 M NaCl solution during one week before of each measurement. Results. Lens power had minimal effect on the ionic permeability of a modern silicone hydrogel contact lens with the -1.00 lens having a 15% lower permeability compared to the other two lenses. After one month of lens wear the apparent ionic permeability for lenses with -1.50 D decreased by 15%. In the case of -1.00 and -4.75 D lenses there was a decrease of 26%. Conclusions. The ionic permeability of silicone hydrogel lenses of different optical powers was not significantly different. Worn lenses present a significant reduction of the ionic permeability after a month of wear. The potential effect this reduction on lens movement and discomfort associated to lens wear should be further evaluated.The authors have no proprietary interest in any of the materials mentioned in this article. This work was funded in part by FEDER through the COMPTETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of projects PTDC/SAU-BEB/098391/2008, PTDC/SAU-BEB/098392/2008 and the Strategic Project PEST-C/FIS/UI607/2011.Ferreira Da Silva, AR.; Compañ Moreno, V.; Gonzalez-Meijome, JM. (2015). Reduction in ionic permeability of a silicone hydrogel contact lenses after one month of daily wear. Materials Research Express. 2(6). https://doi.org/10.1088/2053-1591/2/6/065007S26Yoon, S. C., & Jhon, M. S. (1982). The transport phenomena of some model solutes through postcrosslinked poly(2-hydroxyethyl methacrylate) membranes with different tactic precursors. Journal of Applied Polymer Science, 27(8), 3133-3149. doi:10.1002/app.1982.070270834Yasuda, H., Lamaze, C. E., & Ikenberry, L. D. (1968). Die Makromolekulare Chemie, 118(1), 19-35. doi:10.1002/macp.1968.021180102MURPHY, S., HAMILTON, C., & TIGHE, B. (1988). Synthetic hydrogels: 5. Transport processes in 2-hydroxyethyl methacrylate copolymers. Polymer, 29(10), 1887-1893. doi:10.1016/0032-3861(88)90407-7Nicolson, P. C., & Vogt, J. (2001). Soft contact lens polymers: an evolution. Biomaterials, 22(24), 3273-3283. doi:10.1016/s0142-9612(01)00165-xMonticelli, M. V., Chauhan, A., & Radke, C. J. (2005). The Effect of Water Hydraulic Permeability on the Settling of a Soft Contact Lens on the Eye. Current Eye Research, 30(5), 329-336. doi:10.1080/02713680590934085Guan, L., Jiménez, M. E. G., Walowski, C., Boushehri, A., Prausnitz, J. M., & Radke, C. J. (2011). Permeability and partition coefficient of aqueous sodium chloride in soft contact lenses. Journal of Applied Polymer Science, 122(3), 1457-1471. doi:10.1002/app.33336Cheng, M.-L., & Sun, Y.-M. (2005). Observation of the solute transport in the permeation through hydrogel membranes by using FTIR-microscopy. Journal of Membrane Science, 253(1-2), 191-198. doi:10.1016/j.memsci.2005.01.017CHHABRA, M., PRAUSNITZ, J., & RADKE, C. (2007). A single-lens polarographic measurement of oxygen permeability (Dk) for hypertransmissible soft contact lenses. Biomaterials, 28(30), 4331-4342. doi:10.1016/j.biomaterials.2007.06.024González-Méijome, J. M., López-Alemany, A., Almeida, J. B., & Parafita, M. A. (2009). Surface AFM microscopy of unworn and worn samples of silicone hydrogel contact lenses. Journal of Biomedical Materials Research Part B: Applied Biomaterials, 88B(1), 75-82. doi:10.1002/jbm.b.31153González-Méijome, J. M., López-Alemany, A., Almeida, J. B., & Parafita, M. A. (2008). Dynamic in vitro dehydration patterns of unworn and worn silicone hydrogel contact lenses. Journal of Biomedical Materials Research Part B: Applied Biomaterials, 90B(1), 250-258. doi:10.1002/jbm.b.31279Pozuelo, J., Compañ, V., González-Méijome, J. M., González, M., & Mollá, S. (2014). Oxygen and ionic transport in hydrogel and silicone-hydrogel contact lens materials: An experimental and theoretical study. Journal of Membrane Science, 452, 62-72. doi:10.1016/j.memsci.2013.10.010Wolffsohn, J. S., Hunt, O. A., & Basra, A. K. (2009). Simplified recording of soft contact lens fit. Contact Lens and Anterior Eye, 32(1), 37-42. doi:10.1016/j.clae.2008.12.00

Field effect enhancement in buffered quantum nanowire networks

III-V semiconductor nanowires have shown great potential in various quantum transport experiments. However, realizing a scalable high-quality nanowire-based platform that could lead to quantum information applications has been challenging. Here, we study the potential of selective area growth by molecular beam epitaxy of InAs nanowire networks grown on GaAs-based buffer layers. The buffered geometry allows for substantial elastic strain relaxation and a strong enhancement of field effect mobility. We show that the networks possess strong spin-orbit interaction and long phase coherence lengths with a temperature dependence indicating ballistic transport. With these findings, and the compatibility of the growth method with hybrid epitaxy, we conclude that the material platform fulfills the requirements for a wide range of quantum experiments and applications

Application of ILC super conducting cavities for acceleration of protons

Beam acceleration in the International Linear Collider (ILC) will be provided by 9-cell 1300 MHz superconducting (SC) cavities. The cavities are designed for effective acceleration of charged particles moving with the speed of light and are operated on {pi}-mode to provide maximum accelerating gradient. Significant R&D effort has been devoted to develop ILC SC technology and its RF system which resulted excellent performance of ILC cavities. Therefore, the proposed 8-GeV proton driver in Fermilab is based on ILC cavities above {approx}1.2 GeV. The efficiency of proton beam acceleration by ILC cavities drops fast for lower velocities and it was proposed to develop squeezed ILC-type (S-ILC) cavities operating at 1300 MHz and designed for {beta}{sub G} = 0.81, geometrical beta, to accelerate protons or H{sup -} from {approx}420 MeV to 1.2 GeV. This paper discusses the possibility of avoiding the development of new {beta}{sub G} = 0.81 cavities by operating ILC cavities on 8/9{pi}-mode of standing wave oscillations

Phenomenology of Quantum Gravity and its Possible Role in Neutrino Anomalies

New phenomenological models of Quantum Gravity have suggested that a Lorentz-Invariant discrete spacetime structure may become manifest through a nonstandard coupling of matter fields and spacetime curvature. On the other hand, there is strong experimental evidence suggesting that neutrino oscillations cannot be described by simply considering neutrinos as massive particles. In this manuscript we motivate and construct one particular phenomenological model of Quantum Gravity that could account for the so-called neutrino anomalies.Comment: For the proceedings of "Relativity and Gravitation: 100 Years after Einstein in Prague" (June 2012, Prague