Continuous joint measurement and entanglement of qubits in remote cavities

We present a first-principles theoretical analysis of the entanglement of two superconducting qubits in spatially separated microwave cavities by a sequential (cascaded) probe of the two cavities with a coherent mode, that provides a full characterization of both the continuous measurement induced dynamics and the entanglement generation. We use the SLH formalism to derive the full quantum master equation for the coupled qubits and cavities system, within the rotating wave and dispersive approximations, and conditioned equations for the cavity fields. We then develop effective stochastic master equations for the dynamics of the qubit system in both a polaronic reference frame and a reduced representation within the laboratory frame. We compare simulations with and analyze tradeoffs between these two representations, including the onset of a non-Markovian regime for simulations in the reduced representation. We provide conditions for ensuring persistence of entanglement and show that using shaped pulses enables these conditions to be met at all times under general experimental conditions. The resulting entanglement is shown to be robust with respect to measurement imperfections and loss channels. We also study the effects of qubit driving and relaxation dynamics during a weak measurement, as a prelude to modeling measurement-based feedback control in this cascaded system.Comment: 17 pages, 8 figures. Published versio

A Viable Flavor Model for Quarks and Leptons in RS with T' Family Symmetry

We propose a Randall-Sundrum model with a bulk family symmetry based on the double tetrahedral group, T', which generates the tri-bimaximal neutrino mixing pattern and a realistic CKM matrix. The T' symmetry forbids tree-level flavor-changing-neutral-currents in both the quark and lepton sectors, as different generations of fermions are unified into multiplets of T'. This results in a low first KK mass scale and thus the model can be tested at collider experiments.Comment: 4 pages; based on talk presented at the 17th International Conference on Supersymmetry and the Unification of Fundamental Interactions (SUSY09), Boston, MA, June 5-10, 200

Growth, Welfare, and Public Infrastructure: A General Equilibrium Analysis of Latin American Economies

Empirical studies have found infrastructure investment important for a country¡¯s economic performance, but have not provided clear guidelines for infrastructure policy or its effects on other macroeconomic variables. This paper develops a general equilibrium model of a small open economy to study the effects of public infrastructure on output, private investment and welfare. The model is parameterized and solved for three Latin American countries: Brazil, Mexico, and Peru. Results show that infrastructure can have positive effects on output, private investment and welfare. However, raising public infrastructure investment past a certain threshold can be detrimental. All three countries are shown to have under-invested in infrastructure in the 1970s and 1980s. The gains from optimal infrastructure policy are greatest for Peru, the country with lowest infrastructure expenditure.

Enhanced spin-flip scattering at the surface of copper in lateral spin valves

We performed non-local electrical measurements of a series of Py/Cu lateral spin valve devices with different Cu thicknesses. We show that both the spin diffusion length of Cu and the apparent spin polarization of Py increase with Cu thickness. By fitting the results to a modified spin-diffusion model, we show that the spin diffusion length of Cu is dominated by spin-flip scattering at the surface. In addition, the dependence of spin polarization of Py on Cu thickness is due to a strong spin-flip scattering at the Py/Cu interface

Mirage Torsion

Z_NxZ_M orbifold models admit the introduction of a discrete torsion phase. We find that models with discrete torsion have an alternative description in terms of torsionless models. More specifically, discrete torsion can be 'gauged away' by changing the shifts by lattice vectors. Similarly, a large class of the so-called generalized discrete torsion phases can be traded for changing the background fields (Wilson lines) by lattice vectors. We further observe that certain models with generalized discrete torsion are equivalent to torsionless models with the same gauge embedding but based on different compactification lattices. We also present a method of classifying heterotic Z_NxZ_M orbifolds.Comment: 26 pages, 3 figures, v2: matches version published in JHE

Fusion of engineering, art, and education through an interactive robotic puppet show

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (leaf 11).In this current age of the Technological Revolution, technical proficiency is not enough for graduating engineers and scientists. Creativity and innovation need to be emphasized and pursued. The Robotic Puppet Show fuses engineering, art, and education all in one. The focus of the project is to promote not only interest in math and science for young women, but it includes art to develop creative thinking. The robotic puppets are powered by Vex motors and servos and operated by remote control. After construction of a robotic puppet, I visited a Boston area high school as a guest speaker to demonstrate the robotic puppet's features and abilities, to talk about engineering as a student and in industry, and to gain feedback from students. The robotic puppet was well-received. Human interaction with the robotic puppet played a large part in the students interest. Future plans for the Robotic Puppet Show include developing more personable robots that interact with students on stage. Results indicate that there is potential for successfully teaching robotics to students in this art/engineering approach to both encourage women to pursue engineering and to develop creative thinking that is much needed in today's changing job market.by Heather K. Felix.S.B

The implications from CANGAROO-III observations of TeV blazar PKS 2155-304

We have observed the high-frequency-peaked BL Lacertae object PKS2155-304 in 2004, 2005 and 2006 with the CANGAROO-III imaging atmospheric Cherenkov telescope, and have detected a signal above 660 GeV at the 4.8/sigma level during the 2006 outburst period. Intranight flux variability on time scale of half an hour is observed. From this variability time scale, the size of the TeV gamma-ray emission region is restricted to 5x10^13\delta cm, and the super massive black hole mass is estimated to be less than 1.9x10^8\delta M_{Solar}, where \delta is the beaming factor. The differential energy spectrum is obtained, and an upper limit of the extragalactic infrared background light (EBL) flux is derived under some assumption. We also fit a synchrotron self Compton (SSC) model to the spectral energy distribution (SED) and derive the beaming factor and magnetic field strength.Comment: 4 pages, 5 figures, proceedings of the "4th Heidelberg International Symposium on High Energy Gamma-Ray Astronomy" July 7-11, 2008, Heidelberg, German