Seminar

Careers in Science: Science Policy and General Advice 

Speaker(s): 
Edward Dunlea
Dates: 
Tuesday, April 17, 2018 - 4:30pm to 5:30pm

Considering a career path outside academia? It can be confusing to figure out what else is out there, how to look for jobs, and how to decide what's right for you. Edward Dunlea, Special Assistant to the Dean of MCS, has been down this road and will offer some insights gleaned from his experiences in program management within the government, science policy both at a non-profit and within the private sector, and research administration in academia. His talk will focus on the field of science policy - what it is and how to find jobs - and he will also offer some general advice with an emphasis on careers outside of academia.

Large-Scale Forces and Small-Scale Experiments: Levitated Optomechanics for Precision Gravitational Measurements

Speaker(s): 
Brian D'Urso
Dates: 
Friday, April 13, 2018 - 1:00pm to 2:00pm

We set out to combine a mechanical system in which classical mechanics breaks down and quantum mechanics must be used with a seemingly unlikely application, measurement of the strength and effects of gravity. Our optomechanical system consists of a silica microsphere levitated in ultra-high vacuum in a magneto-gravitational trap. The microsphere is trapped in a magnetic field gradient created by permanent magnets and ferromagnetic pole pieces using the weak diamagnetism of the particle. With optical position measurements and feedback, the mechanical motion can be cooled by several orders of magnitude, ideally reaching the quantum ground state. The extreme sensitivity of this optomechanical system to external forces makes it a promising approach to a new measurement of the Newtonian gravitational constant. Furthermore, by measuring the decoherence rate of non-classical motional states of the trapped particle, it may be possible to place limits on theories of gravitational decoherence. This material is based upon work supported by the National Science Foundation under Grant No. 1757005

In Pursuit of an Immortal Cathode: Electrical Energy Storage using MnO2 Nanowires that Never Die

Speaker(s): 
Reginald Penner
Dates: 
Friday, March 16, 2018 - 9:30am to 10:30am

Rechargeable lithium ion (Li+) batteries lose their ability to store charge over time.  Whether they power your phone, your laptop, or your automobile, after 500-1000 recharge cycles they lose 20-40% of their capacity and must be replaced. Sony introduced the first commercial  Li+ battery in 1990, but 27 years later our understanding of WHY they fail is still in its infancy.  Li+ batteries have four parts:  An anode (usually graphite), a cathode (usually a metal oxide), a separator membrane that is located between them, and a salt solution containing Li+.  In our research, we have focused attention on one cathode material called ∂-MnO2.   Our goals have been to increase the amount of energy we can store, to increase the rate at which we can deliver this energy, and to extend the lifetime of the cathode.  Now, you might think that the worst way to make a battery cathode last longer would be to make it smaller!  But we have discovered a process for preparing ∂-MnOnanowires  - just 60 – 600 nm in diameter and up to a centimeter in length – that never fail, and rarely lose any energy storage capacity, across 100,000 charge/recharge cycles.   In this talk, I’ll discuss these unusual nanomaterials and what they may mean for the future of electrical energy storage.

Mermin in Bananaworld: Bub on Quantum Mechanics

Speaker(s): 
Michel Janssen
Dates: 
Tuesday, March 13, 2018 - 12:00pm to 1:00pm

 In the 1980s, David Mermin derived a simple example of a Bell inequality and showed that it is violated in measurements on entangled quantum systems. In this talk, I reanalyze Mermin’s example, using correlation arrays, the workhorse in Jeffrey Bub’s Bananaworld (2016). For the class of all non-signaling correlations conceivable in the kind of experiment considered by Mermin, I derive both the Bell inequality, a necessary condition for such correlations to be allowed classically, and the Tsirelson bound, a necessary condition for them to be allowed quantum-mechanically. I show that the Tsirelson bound for these experiments follows directly from the geometry going into their quantum-mechanical analysis. I use this example to promote Bubism (not to be confused with QBism though both are information-theoretic approaches to the foundations of quantum mechanics). I do so by comparing the rules for probabilities in quantum mechanics, illustrated by my Bubist reanalysis of Mermin’s example, to the rules for spatio-temporal behavior in special relativity.

Molecular Clusters: Building Blocks for Nanoelectronics and Material Design

Speaker(s): 
Xavier Roy
Dates: 
Thursday, April 5, 2018 - 4:30pm to 5:30pm

The programmed assembly of nanoscale building blocks offers exciting new avenues to creating electronic devices and materials in which structure and functions can be chemically designed and tuned. In this context, the synthesis of inorganic molecular clusters with atomically-defined structures, compositions and surface chemistry provides a rich family of functional building elements. This presentation will describe our efforts to assemble such “designer atoms” into a variety of hierarchical structures and devices, and study the resulting collective properties.

Coherent quantum critical dynamics in a driven Bose-Einstein condensate

Speaker(s): 
Cheng Chin
Dates: 
Friday, April 20, 2018 - 3:45pm to 5:00pm

Quantum phase transitions are transitions between distinct many-body ground states, and are of extensive interest in research ranging from condensed matter physics to cosmology. Key features of the phase transitions include a stage with rapidly growing new order, called inflation in cosmology, followed by the formation of topological defects. Based on Bose-Einstein condensates of cesium atoms in a shaken lattices [1], we report the observation of universal scaling of quantum critical dynamics [2], and inflationary dynamics across a quantum phase transition [3]. In particular, the inflation...

Machine learning approaches to entangled quantum states

Speaker(s): 
Xiaopeng Li
Dates: 
Friday, March 16, 2018 - 1:30pm to 2:30pm

Artificial neural networks play a prominent role in the rapidly growing field of machine learning and are recently introduced to quantum many-body systems. This talk will focus on using a machine-learning model, the restricted Boltzmann machine (RBM) to describe entangled quantum states. Both short- and long-range coupled RBM will be discussed. For a short-range RBM, the associated quantum state satisfies an entanglement area law, regardless of spatial dimensions. I will present our recently constructed exact RBM models for nontrivial topological phases, including a 1d...

Quantum Phenomena in Two-Dimensional Materials Driven by Atomic Scale Modifications

Speaker(s): 
Jyoti Katoch
Dates: 
Monday, February 19, 2018 - 4:30pm to 5:30pm

The extreme surface sensitivity of two-dimensional (2D) materials provides an unprecedented opportunity to engineer the physical properties of these materials via changes to their surroundings, including a substrate, adsorbates, defects, etc.  In particular, the decoration of the 2Dmaterial with adatoms can be utilized to tailor material properties and induce novel quantum phenomena. In this context, first I will discuss the case of 2D semiconducting transition metal dichalcogenides (TMDs), wherein new electronic phenomena such as tunable bandgaps and strongly bound...

Current Instability in a Driven 2D Electron Liquid Probed by Nanoscale Magnetometry

Speaker(s): 
Javier Sanchez-Yamagishi
Dates: 
Thursday, February 15, 2018 - 4:30pm to 5:30pm

A moving fluid can become unstable in the presence of an obstruction, leading to a flow pattern that fluctuates in time due to nonlinear dynamics.  It has been recently found that some materials host electrons that behave like a collective fluid. In particular, experiments with graphene electrons have demonstrated linear hydrodynamic phenomena, such as viscous drag at sample boundaries, but nonlinear effects have yet to be reported.  We observe a AC current instability that develops when driving a DC current through a graphene device in the electron hydrodynamic regime...

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