Surface Acoustic Wave induced Transport in a Double Quantum Dot

We report on non-adiabatic transport through a double quantum dot under irradiation of surface acoustic waves generated on-chip. At low excitation powers, absorption and emission of single and multiple phonons is observed. At higher power, sequential phonon assisted tunneling processes excite the double dot in a highly non-equilibrium state. The present system is attractive for studying electron-phonon interaction with piezoelectric coupling.Comment: 4 pages, 3 figure

Entanglement distillation by adiabatic passage in coupled quantum dots

Adiabatic passage of two correlated electrons in three coupled quantum dots is shown to provide a robust and controlled way of distilling, transporting and detecting spin entanglement, as well as of measuring the rate of spin disentanglement. Employing tunable interdot coupling the scheme creates, from an unentangled two-electron state, a superposition of spatially separated singlet and triplet states. A single measurement of a dot population (charge) collapses the wave function to either of these states, realizing entanglement to charge conversion. The scheme is robust, with the efficiency close to 100%, for a large range of realistic spectral parameters.Comment: 5 pages, 4 figure

Gas signatures of Herbig Ae/Be disks probed with Herschel SPIRE spectroscopy

Herbig Ae/Be objects, like their lower mass counterparts T Tauri stars, are seen to form a stable circumstellar disk which is initially gas-rich and could ultimately form a planetary system. We present Herschel SPIRE 460-1540 GHz spectra of five targets out of a sample of 13 young disk sources, showing line detections mainly due to warm CO gas.Comment: to be published in proceedings of IAU symposium 299 (Victoria, BC, Canada, June 2013

Exchange-controlled single-electron-spin rotations in quantum dots

We show theoretically that arbitrary coherent rotations can be performed quickly (with a gating time ~1 ns) and with high fidelity on the spin of a single confined electron using control of exchange only, without the need for spin-orbit coupling or ac fields. We expect that implementations of this scheme would achieve gate error rates on the order of \eta ~ 10^{-3} in GaAs quantum dots, within reach of several known error-correction protocolsComment: 4+ pages, 3 figures; v2: Streamlined presentation, final version published in PRB (Rapid Comm.

Modeling association between DNA copy number and gene expression with constrained piecewise linear regression splines

DNA copy number and mRNA expression are widely used data types in cancer studies, which combined provide more insight than separately. Whereas in existing literature the form of the relationship between these two types of markers is fixed a priori, in this paper we model their association. We employ piecewise linear regression splines (PLRS), which combine good interpretation with sufficient flexibility to identify any plausible type of relationship. The specification of the model leads to estimation and model selection in a constrained, nonstandard setting. We provide methodology for testing the effect of DNA on mRNA and choosing the appropriate model. Furthermore, we present a novel approach to obtain reliable confidence bands for constrained PLRS, which incorporates model uncertainty. The procedures are applied to colorectal and breast cancer data. Common assumptions are found to be potentially misleading for biologically relevant genes. More flexible models may bring more insight in the interaction between the two markers.Comment: Published in at http://dx.doi.org/10.1214/12-AOAS605 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Nonadiabatic Electron Manipulation in Quantum-Dot Arrays

A novel method of coherent manipulation of the electron tunneling in quantum-dots is proposed, which utilizes the quantum interference in nonadiabatic double-crossing of the discrete energy levels. In this method, we need only a smoothly varying gate voltage to manipulate electrons, without a sudden switching-on and off. A systematic design of a smooth gate-pulse is presented with a simple analytic formula to drive the two-level electronic state to essentially arbitrary target state, and numerical simulations for complete transfer of an electron is shown for a coupled double quantum-dots and an array of quantum-dots. Estimation of the manipulation-time shows that the present method can be employed in realistic quantum-dots

Emergence of a negative charging energy in a metallic dot capacitively coupled to a superconducting island

We consider the hybrid setup formed by a metallic dot, capacitively coupled to a superconducting island S connected to a bulk superconductor by a Josephson junction. Charge fluctuations in S act as a dynamical gate and overscreen the electronic repulsion in the metallic dot, producing an attractive interaction between two additional electrons. As the offset charge of the metallic dot is increased, the dot charging curve shows positive steps ($+2e$) followed by negative ones ($-e$) signaling the occurrence of a negative differential capacitance. A proposal for experimental detection is given, and potential applications in nanoelectronics are mentioned.Comment: Revised version, 4 pages, 4 figure

Symbolic computation and exact distributions of nonparametric test statistics

We show how to use computer algebra for computing exact distributions on nonparametric statistics. We give several examples of nonparametric statistics with explicit probability generating functions that can be handled this way. In particular, we give a new table of critical values of the Jonckheere-Terpstra test that extends tables known in the literature

Theory of a two-level artificial molecule in laterally coupled quantum Hall droplets

We present a theory of laterally coupled quantum Hall droplets with electron numbers (N1,N2) at filling factor $\nu=2$. We show that the edge states of each droplet are tunnel coupled and form a two-level artificial molecule. By populating the edge states with one electron each a two electron molecule is formed. We predict the singlet-triplet transitions of the effective two-electron molecule as a function of the magnetic field, the number of electrons, and confining potential using the configuration interaction method (CI) coupled with the unrestricted Hartree-Fock (URHF) basis. In addition to the singlet-triplet transitions of a 2 electron molecule involving edge states, triplet transitions involving transfer of electrons to the center of individual dots exist for $(N1 \geq 5, N2 \geq 5)$.Comment: 5 pages, 10 figure