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

Information Complements, Substitutes, and Strategic Product Design

Competitive maneuvering in the information economy has raised a pressing question: how can firms raise profits by giving away products for free? This paper provides a possible answer and articulates a strategy space for information product design. Free strategic complements can raise a firm's own profits while free strategic substitutes can lower profits for competitors. We introduce a formal model of cross-market externalities based in textbook economics -- a mix of Katz & Shapiro network effects, price discrimination, and product differention -- that leads to novel strategies such as an eagerness to enter into Bertrand price competition. This combination helps to explain many recent firm strategies such as those of Microsoft, Netscape (AOL), Sun, Adobe, and ID. We also introduce the concept of a ''content-creator'' who adds value for end-consumers but may not be paid directly. Similar to the case of product dumping, this research implies that both firms and policy makers need to consider complex market interactions to grasp information product design and profit maximization. The model presented here argues for three simple and intuitive results. First, a firm can rationally invest in a product it intends to give away into perpetuity even in the absence of competition. The reason is that increased demand in a complementary goods market more than covers the cost of investment in the free goods market. Second, we identify distinct markets for content-providers and end-consumers and show that either can be a candidate for the free good. The decision on which market to charge rests on the relative elasticities as governed by their network externality effects. If the externality effect is sufficiently great, the market with the higher elasticity is the market to subsidize with the free good. It is also possible to charge both markets but to keep one price artificially low. Importantly, the modeling contribution is distinct from tying in the sense that consumers need never purchase both goods -- unlike razors and blades, the products are stand-alone goods. It also differs from multi-market price discrimination in the sense that the firm may extract no consumer surplus from one of the two market segments, implying that this market would have previously gone un-served. Third, a firm can use strategic product design to penetrate a market that becomes competitive post-entry. The threat of entry is credible even in cases where it never recovers its sunk costs directly. The model therefore helps to explain several interesting market behaviors such as free goods, upgrade paths, split versioning, and strategic information substitutes.http://deepblue.lib.umich.edu/bitstream/2027.42/39683/3/wp299.pd

The connection between noise and quantum correlations in a double quantum dot

We investigate the current and noise characteristics of a double quantum dot system. The strong correlations induced by the Coulomb interaction create entangled two-electron states and lead to signatures in the transport properties. We show that the interaction parameter phi, which measures the admixture of the double-occupancy contribution to the singlet state and thus the degree of entanglement, can be directly accessed through the Fano factor of super-Poissonian shot noise.Comment: 5 pages, major revision, to be published in Phys. Rev.

Arrest of flow and emergence of activated processes at the glass transition of a suspension of particles with hard sphere-like interactions

By combining aspects of the coherent and self intermediate scattering functions, measured by dynamical light scattering on a suspension of hard sphere-like particles, we show that the arrest of particle number density fluctuations spreads from the position of the main structure factor peak. Taking the velocity auto-correlation function into account we propose that as density fluctuations are arrested the system's ability to respond to diffusing momentum currents is impaired and, accordingly, the viscosity increases. From the stretching of the coherent intermediate scattering function we read a quantitative manifestation of the undissipated thermal energy, the source of those, ergodicity restoring, processes that short-circuit the sharp transition to a perfect glass.Comment: 9 pages, 4 figure

Geometric B\"acklund--Darboux transformations for the KP hierarchy

We shown that, if you have two planes in the Segal-Wilson Grassmannian that have an intersection of finite codimension, then the corresponding solutions of the KP hierarchy are linked by B\"acklund-Darboux transformations (BDT). The pseudodifferential operator that performs this transformation is shown to be built up in a geometric way from elementary BDT's and is given here in a closed form. The geometric description of elementary DBT's requires that one has a geometric interpretation of the dual wavefunctions involved. This is done here with the help of a suitable algebraic characterization of the wavefunction. The BDT's also induce transformations of the tau-function associated to a plane in the Grassmannian. For the Gelfand-Dickey hierarchies we derive a geometric characterization of the BDT'ss that preserves these subsystems of the KP hierarchy. This generalizes the classical Darboux-transformations. we also determine an explicit expression for the squared eigenfunction potentials. Next a connection is laid between the KP hierarchy and the 1-Toda lattice hierarchy. It is shown that infinite flags in the Grassmannian yield solutions of the latter hierarchy. these flags can be constructed by means of BDT's, starting from some plane. Other applications of these BDT's are a geometric way to characterize Wronskian solutions of the $m$-vector $k$-constrained KP hierarchy and the construction of a vast collection of orthogonal polynomials, playing a role in matrix models.Comment: 44 pages Latex2