Fall 2018

September 21, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Jay D. Sau, University of Maryland
Host: E. Rossi
Title: Search for the new exotic quantum particle: Non-Abelian Majorana zero modes at semiconductor-superconductor interfaces
Abstract: Majorana zero modes are fermion-like excitations that were originally proposed in particle physics by Ettore Majorana and are characterized as being their own anti-particle. In condensed matter systems Majorana zero modes occur as fractionalized excitations with topologically protected degeneracy associated with such excitations. For over a decade the only candidate systems for observing Majorana zero modes were the non-Abelian  fractional quantum Hall state and chiral p-wave superconductors. In this talk, I will discuss a recent set of proposals for realizing Majorana zero modes in a large class of spin-orbit coupled, time-reversal symmetry broken superconducting systems. The simplicity of this class of systems has resulted in several experimental attempts, which have successfully observed preliminary evidence for the Majorana zero modes in the form of zero-bias conductance peaks and the fractional Josephson effect. Following this I will discuss future possibilities in terms of modifications to the experiments to help confirm the presence of Majorana zero modes through more dramatic signatures.

September 28, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Danielle Speller, Yale
Host: C. Carone
Title:  Invisible Worlds:  A Search For Axion Dark Matter with the HAYSTAC Experiment
Abstract: The nature of dark matter is one of the most elusive puzzles in modern physics.  With the absence of the detection of traditional candidates like the WIMP, there has been a strong resurgence of interest in low mass and very light candidates, such as the axion. The Haloscope At Yale Sensitive To Axion CDM (HAYSTAC) is a tunable microwave cavity experiment sensitive to significant regions of the axion parameter space interesting to both particle physics and cosmology.  In 2017, the HAYSTAC experiment excluded axion-photon couplings above ~2x10-14 GeV-1 for axion masses between 23.15 < m< 24.0 𝜇eV, a mass range previously unexplored by existing haloscope experiments.  HAYSTAC is now entering its next stage of operation, incorporating a new squeezed-state receiver system and significant upgrades to the cryogenics system.  We discuss our recent results, upgrades, current status, and commissioning for Phase II. 

October 5, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Gail McLaughlin, North Carolina State University
M. Sher
Nuclear and neutrino physics of the r-process
Abstract: The production of the elements heavier than iron in the universe has long been associated with neutron-capture processes. The most neutron-rich isotopes are created by rapid (r ) neutron-capture nucleosynthesis in extreme astrophysical environments. Specifics of these environments and the location of the astrophysical sites in which the r process occurs have remained open problems. It has been reported that observations of the gravitational wave event GW170817 and its electromagnetic counterpart suggest that neutron star mergers are a site of r-process nucleosynthesis. Still many questions remain, such as the nature of the astrophysical conditions within the merger responsible for element synthesis and whether mergers can account for all galactic r-process production. If we hope to fully understand the connection between this discovery and the origin of r-process elements, uncertainties in neutrino and nuclear astrophysics must be reduced. I will highlight the role played by neutrinos and nuclear masses.

October 12, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Andrey Antipov, Microsoft Station Q
Host: E. Rossi
Title:  Majorana quasiparticles in the quantum computing quest
Abstract: The future progress of science and technology requires general solutions for quantum problems. Some of these problems, such as the design of advanced materials, in specific cases can be treated by classical computers, but often approximately or at exponentially high cost. In general a dedicated quantum device is needed, i.e. a quantum computer. To really solve complex problems these computers need to be scalable and increase their computational power with the number of elementary information units - qubits. This puts strict requirements on the quality of qubit hardware. In particular the qubits should not change their state at random during a computation, i.e. they should not react to the external noise. Quantum systems with fractionalized excitations, in particular, Majorana zero modes have been long sought as great candidates to serve as a qubit platform as they offer an exponential protection from external noise. In this talk I will review the recent progress done at Microsoft to demonstrate and utilize systems with Majorana zero modes as a qubit platform.

October 26, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Tim Tait, UC Irvine
Host: M. Sher
Title: Searching for Particle Dark Matter
Abstract: I will discuss the mysterious dark matter which observations indicate makes up most of the matter in the Universe, but whose fundamental nature remains unknown.  I will explain how different particle physics search techniques provide key information, and ultimately can work together to provide a composite image which is greater than its component parts.

November 2, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Prof. Fukuyama, Professor Emeritus, Department of Nuclear Engineering, Kyoto University, Kyoto, Japan
Host: S. Sen/ G. Vahala
Title:  A new approach to kinetic full wave analysis in inhomogeneous plasmas
Abstract: Various kinds of electromagnetic waves are excited in plasmas, internally as an instability or externally for control purpose. In order to describe the wave structure in bounded plasmas, full wave analysis which solves Maxwell’s equation as a boundary-value problem has been widely utilized. In finite-temperature plasmas, however, it is not straight-forward to include the wave-plasma interaction in the full wave analysis. In a homogeneous plasma, the plasma response to waves, dielectric tensor, is usually expressed as a function of wave number. In an inhomogeneous plasma, however, the wave number is not constant and the thermal particle motion leads to spatial coupling. Therefore, the differential operator approach and the Fourier transform approach have been developed and employed in spite of limitation in applicability. In this talk, a new approach to the kinetic full wave analysis based on the dielectric tensor in the form of integral operator is introduced and three applications are presented. This approach is free from wave number, and the spatial coupling is limited within the range of particle motion. After a brief survey of full wave modeling in plasmas, physics and formulation of the integral operator approach are explained. The first example is the laser-plasma resonant interaction in unmagnetized nonuniform hot plasmas. The incident electromagnetic wave excites the plasma wave at the plasma resonance and the latter is absorbed by collisionless Landau damping. The incident angle dependence of the absorption rate and the deposition profiles are compared with those of conventional collisional damping model. It was found that, with a steep density gradient, stochastic heating occurs even in the case of normal incidence. The second example is the cyclotron damping in the magnetic beach heating. The absorption profile near the cyclotron resonance is obtained. The third example is the finite gyro-radius effects. One-dimensional full wave analysis is applied to the analysis of the O-X-B (ordinary wave, extra-ordinary wave, Bernstein wave) linear mode conversion of electron cyclotron waves in a tokamak plasma con- figuration. Finally, several remaining issues are discussed: two-dimensional kinetic full wave analysis, arbitrary velocity distribution function, and quasi-linear diffusion in the velocity space.
November 9, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: P. Vahle, William & Mary Physics
Host: M. Kordosky
Title: New results from accelerator neutrino oscillation experiments
Abstract: Neutrino oscillations provide the first hints at physics beyond the standard model of particle physics.  Current and future neutrino experiments aim to further refine our understanding of neutrino mixing and reveal the remaining unknowns in the process.  Precision measurements in long-baseline accelerator experiments could help answer profound questions about the origin and evolution of our universe, including the assymetry of matter over antimatter.  The NOvA experiment at Fermilab uses a beam of neutrinos and two detectors separated by an 810 km baseline to observe muon neutrino disappearance and electron neutrino appearance.  These measurements have the potential to resolve the ordering of the neutrino masses, called the hierarchy, determine whether the mixing angle theta_23 is maximal, and if not in which octant it lies, and perhaps even hint at the violation of CP in the neutrino sector.  In this talk, I'll describe the current status of accelerator oscillation experiments seeking to answer these questions, and in particular present new results from the NOvA experiment.
November 16, 2018 (Friday) 4:00-5:00p.m. Small Hall 111
Speaker: Javad Shabani, Center for Quantum Phenomena, Physics Department, New York University, New York, 10003
Host: E. Rossi
Title: Superconducting proximity effect in two-dimensional semiconductor-superconductor structures
Abstract: Progress in the emergent field of topological superconductivity relies on synthesis of new material combining superconductivity, low density, and spin-orbit coupling. Theory indicates that the interface between a one-dimensional semiconductor with strong SOC and a superconductor hosts Majorana-modes with nontrivial topological properties. We present our recent developments in materials synthesis and growth of density-controlled surface 2D InAs quantum wells with epitaxial superconducting Aluminum. These developments have led to unprecedented control over proximity effect in semiconductors where electron densities can be tuned using a gate voltage. We demonstrate Josephson junctions with IV characteristic indicating highly transparent contacts. We focus on multiterminal junctions and superconducting quantum interference device (SQUID) geometry to investigate the subtle interplay between supercurrents and spin orbit interaction in these materials. The amplitude and shape of current phase plot is varied as critical currents in each arm are independently controlled using gate-tunable junctions. The data can be well described using solution of Bogoliubov–de Gennes equation for our SQUID junctions. We discuss potential applications in gate-based qubits as well as exploring topological superconductivity for computation.