Seminar

Phase-change photonics for all-optical memory, computation, and beyond

Speaker(s): 
Dr. Nathan Youngblood
Dates: 
Wednesday, October 2, 2019 - 12:00pm

Phase-change chalcogenides (such as AgInSbTe and Ge2Sb2Te5) have been used commercially as an optical storage medium in the last few decades owing to their high optical contrast and long-term stability, but only recently has a fully integrated photonic device been demonstrated. This approach not only enables all-optical memory on-chip, but also allows multilevel data storage with improved SNR, low switching energy, and high speed operation. In the first part of this talk, new innovations in phase-change, non-volatile photonic memory will be presented, including their use for “in-memory”...

Chromophore Packing and Singlet Fission Rates

Speaker(s): 
Josef Michl
Dates: 
Thursday, December 5, 2019 - 4:00pm

Results of a theoretical examination of the effect of crystal packing on singlet fission (SF) rate are presented.  For a model system (pair of ethylenes) and several known or suspected SF materials: tetracene (1), cibalackrot (2), and 1,3-diphenylisobenzofuran (3), we predict molecular pair arrangements that are especially favorable for the rate of SF.  The predictions are obtained from an approximate evaluation of squares of SF eectronic matrix elements, based on a complete search of all possible pair packing geometries.  This is refined by an evaluation of...

Don't Cry Over Spilled Entropy

Speaker(s): 
Stefano Curtarolo
Dates: 
Friday, October 4, 2019 - 11:30am

Critical understanding of large amount of data exposes the unavoidability of disorder and leads to new descriptors for discovering entropic materials. The formalism, based on the energy distribution spectrum of randomized calculations, captures the accessibility of equally-sampled states near the ground state and quantifies configurational disorder capable of stabilizing high-entropy homogeneous phases. The methodology - applied to disordered refractory 5-metal carbides (promising candidates for high-hardness, high melting point applications) – uncovers scientific surprises. Directions for...

Quantum quench and nonequilibrium dynamics in lattice-confined spinor Bose-Einstein condensates

Speaker(s): 
Yingmei Liu
Dates: 
Monday, October 21, 2019 - 4:00pm

Bose-Einstein condensates (BECs) are ultra-cold gases, in which all atoms have a single collective wavefunction for their spatial degrees of freedom. With an additional spin degree of freedom, spinor BECs constitute a collective quantum system offering an unprecedented degree of control over such parameters as spin, density, temperature, and the dimensionality of the system. Spinor BECs have thus been considered as good quantum simulators for verifying and optimizing condensed matter models. In this talk, I will discuss a novel quantum phase transition realized in our antiferromagnetic...

Integrated Photonic Circuits for Classical and Quantum Information Processing

Speaker(s): 
Qing Li
Dates: 
Wednesday, September 25, 2019 - 12:00pm

In addition to being the most successful material for electronics, silicon is also an excellent photonic material receiving widespread interest from both academia and industry. Following the tremendous success enjoyed by integrated electronics, integrated photonic circuits in silicon hold the promise of device scaling, mass fabrication, and system-level integration, which could revolutionize many traditional photonic technologies and create a wealth of practical applications. In this talk, I will provide several such examples focused on classical and quantum information processing. In the...

Thoroughly Modern Zeno: The Arrow, Quantum Mechanically

Speaker(s): 
Laura Ruetsche
Dates: 
Friday, November 8, 2019 - 3:30pm

In the 5th century BCE, Zeno of Elea devised dozens of arguments against the possibilities of motion, change, and plurality. The loveliest of these, the Arrow Paradox, is briefly stated: "The flying arrow is motionless." In 1970, Wes Salmon published an anthology devoted to Zeno's Paradoxes and amply demonstrating their capacity to reward scrutiny from the perspectives afforded by mathematics and physics as they themselves move forward. Wes's introduction to that anthology was my first assignment in my first philosophy course. In 2019, I'll try to demonstrate that Zeno's paradoxes continue...

Diagnosing quantum chaos in many-body systems using entanglement

Speaker(s): 
Marcel Franz
Dates: 
Tuesday, December 3, 2019 - 1:30pm

Classical chaotic systems exhibit exponentially diverging trajectories due to small differences in their initial state. The analogous  diagnostic in quantum many-body systems is an exponential growth of  out-of-time-ordered correlation functions (OTOCs). These quantities can  be computed for various models, but their experimental study requires the ability to evolve quantum states backward in time, similar to the  canonical Loschmidt echo measurement. In some simple systems, backward time evolution can be achieved by reversing the sign of the Hamiltonian; however in most interacting many-...

Artificial Atoms: Quantum Optics and Spin Physics of Quantum Dots

Speaker(s): 
Edward (Ned) Flagg
Dates: 
Thursday, October 3, 2019 - 4:00pm

Semiconductor quantum dots (QDs) are nanoscopic crystals that are often called artificial atoms. Charge carriers trapped within them have discrete energy levels in the fashion of single atoms, and they absorb and emit light at discrete wavelengths corresponding to those energy levels. Because of this, in many ways QDs behave like the canonical two-level quantum system, which makes them suitable for experiments involving the quantum nature of light, which is called quantum optics. For this reason and for their potential uses in quantum information applications, QDs attract great scientific...

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