Seminar

Infrared Radiation for Healthy Living: Disease Diagnostics 

Speaker(s): 
A. G. Unil Perera
Dates: 
Friday, May 18, 2018 - 10:30am to 11:30am

The incidence rates of cancers and other chronic diseases have been increasing in many regions and populations.  There are more than 70,000 new cases of inflammatory bowel diseases (IBD) such as ulcerative colitis, diagnosed every year. Established diagnostic techniques for cancers and ulcerative colitis are invasive, cause discomfort, and are not cost-effective. The compliance rate for the screening of such diseases is very small due to this discomfort, expense, and the risk of complications. Thus, it is important to develop minimally invasive or noninvasive and cost-effective prescreening strategies.   

Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy accompanied with different data analysis frameworks can provide an excellent spectroscopic technology to extract biochemical information from bio-fluids which can lead to the identification of diseases. Results show that dried serum samples can be used to detect the biochemical changes induced by cancers and IBDs. This potential technology can be further developed into a noninvasive, personalized diagnostic tool in which patient-to-patient differences in molecular signatures would allow the assessment of disease status and personalized drug management.  

Ultra-Fast Relaxation, Decoherence, and Localization of Photoexcited States in p-Conjugated Polymers

Speaker(s): 
William Barford
Dates: 
Thursday, May 10, 2018 - 4:30pm to 5:30pm

We investigate the energetic relaxation and spatial localization of photoexcited states in conformationally disordered p-conjugated models, choosing poly(para-phenylene vinylene) as a model system. Assuming vertical excitations, the initial photoexcited eigenstates are obtained via the disordered Frenkel model. The subsequent relaxation and localization of the excited statesis determined via the disordered Frenkel-Holstein model coupled to a dissipative environment. In particular, we solve the Lindblad master equation via the time-evolving block decimation (TEBD) and quantum jump trajectory methods.

The values of the model parameters physically relevant to polymer systems naturally lead to a separation of time scales, with the ultra-fast dynamics corresponding to energy transfer from the exciton to the internal phonon modes (i.e., the C-C bond oscillations), while the longer time dynamics correspond to damping of these phonon modes by the external dissipation. Associated with these time scales, we investigate the following processes that are indicative of the system relaxing onto the emissive chromophores of the polymer: 1) Exciton-polaron formation occurs on an ultra-fast time scale, with the associated exciton-phonon correlations present within half a vibrational time period of the C-C bond oscillations. 2) Exciton decoherence is driven by the decay in the vibrational overlaps associated with exciton-polaron formation, occurring on the same time scale. 3) Exciton density localization is driven by the external dissipation, arising from ‘wavefunction collapse’ occurring as a result of the system-environment interactions. Finally, we show how fluorescence anisotropy measurements can be used to investigate the exciton decoherence process during the relaxation dynamics.

Open system approaches for quantum transport through tunneling junctions

Speaker(s): 
François Damanet
Dates: 
Thursday, April 26, 2018 - 4:00pm

Quantum transport is a key area in quantum physics which presents challenges in terms of theoretical description. In this talk, I will present how the non-equilibrium dynamics of tunneling junctions weakly coupled to baths of fermionic or bosonic particles can be investigated using open system approaches, namely input-output formalisms and master equations. As a specific example, I will first present our study of electron transport in a quantum dot tunneling junction connecting two normal or superconducting leads, where both single-particle and Cooper-pair tunneling are considered. In particular, I will show how signatures of Andreev bound states can be obtained in the output currents. Then, I will present our results on spin transport in a quadratic spin system connecting baths modeled as XXZ spin chains. Based on non-Markovian master equations for the system and t-Matrix Product States simulations to compute the bath correlation functions, we showed that the spin current through the system can be enhanced due to the presence of the interaction in the baths as well as exhibit transient rectification (i.e. different current under bias exchange). Finally, I will sketch a more general outlook on how non-Markovian master equations could be used to study the transport properties of a system of unknown spectrum, which is particularly useful for the case of complicated time-dependent or many-body system Hamiltonians.

Accelerating Your Research with No-Cost Resources for Computing, AI, and Data with PSC

Speaker(s): 
Nick Nystrom
Dates: 
Wednesday, May 9, 2018 - 3:30pm to 4:30pm

Pittsburgh Supercomputing Center (PSC) offers powerful resources for computing, artificial intelligence, and data management and analytics that are available at no charge for open research and to support coursework. In this talk, we will survey examples of breakthroughs that are using PSC resources and ways to leverage PSC for your own research. Examples will highlight successes in genomics, AI, neuroscience, engineering, and other fields. We will highlight two PSC resources that provide unique capabilities: Bridges and Anton 2. Bridges converges high-performance computing (HPC), artificial intelligence (AI), and Big Data and offers a familiar, an exceptionally flexible user environment, applicable to whatever data analytics or simulation exceed groups’ local capabilities. Anton 2 is a special-purpose computer that dramatically increases the speed of molecular dynamics (MD) simulations to understand the motions and interactions of proteins and other biologically important molecules over much longer time periods than would otherwise be accessible. We will also describe Compass AI, a new initiative to help the community make the most of emerging hardware and software technologies for AI, develop best practices, provide education and training, and establish collaborations, especially between academia and the private sector. We outline areas of expertise at PSC where we are conducting research and open to additional collaboration. We close with a summary of opportunities to co-locate computational resources at PSC, with possible benefits of saving money, bursting to larger resources when needed, and leveraging PSC’s broad software collection. 

A number of PSC’s scientific staff will be present for discussion at the reception following the seminar. A reception will follow at 4:30pm

Two Dimensional Quantum Materials - An Atomically Thin Platform for Spintronics and Novel Spin Phenomena 

Speaker(s): 
Simranjeet Singh
Dates: 
Tuesday, May 1, 2018 - 4:30pm to 5:30pm

Two dimensional (2D) quantum materials provide a versatile experimental platform to probe spin-dependent novel quantum phenomena emerging at the nanoscale. The possibility of on-demand tuning of spin properties of 2D materials by external knobs such as electric field, substrate engineered proximity, etc., can have far-reaching implications for spintronics. I will discuss our experiments demonstrating a strong modulation of spin currents in bilayer graphene using static and fluctuating proximity exchange fields of a ferromagnetic insulator (FMI). We achieve complete spin modulation in graphene layers by controlling the direction of the exchange field of a nearby magnetic material in graphene/FMI heterostructures. A strong magnetic exchange coupling across the interface in graphene/FMI heterostructures leads to the experimental observation of full spin modulation at low externally applied magnetic fields in mesoscopic graphene spin channels. In graphene/FMI heterostructures, we also discover a novel spin dephasing mechanism due to randomly fluctuating magnetic exchange fields. This is manifested as an unusually strong temperature dependence of the non-local spin signals in graphene, which is due to spin relaxation by thermally-induced transverse fluctuations of the FMI magnetization. 

In the second half of my talk, I will discuss spin-charge interconversion driven by the Rashba effect in van der Waal bonded platinum/graphene (Pt/Gr) heterostructures. The interfacial spin-orbit interaction driven Rashba effect in low-dimensional systems can enable efficient and tunable spin-charge interconversion for spintronics applications. I will show that an applied electric field at the Pt/Gr Rashba interface results in a net spin accumulation in graphene, with spin polarization quantized along a direction transverse to the applied electric field. This current induced non-zero spin accumulation at the Pt/Gr interface is a direct consequence of uncompensated spin-textured Femi surfaces of the graphene Dirac states due to a symmetry-breaking electric field normal to the Pt/Gr heterostructure. Employing the Pt/Gr Rashba interface, we also realize the first experimental demonstration of the Onsager reciprocity between charge and spin via Rashba Edelstein effect (REE) and inverse-REE. This work is a significant advancement in graphene spintronics and provides an alternative experimental approach to generating and detecting spins using extrinsically tunable interfacial spin-orbit phenomena in two-dimensional materials.

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.

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