aspuru-list April 2015

aspuru-list@lists.fas.harvard.edu

28 participants
68 discussions

[Aspuru-Guzik group list] Excitonics Seminar, TODAY- Apr 21, 4:30, 36-428

by Catherine M Bourgeois

Please post and forward to your groups TODAY CENTER FOR EXCITONICS Seminar Series Spectroscopy and Topological Phases for Organic Excitons April 21, 2015 at 4:30 PM/ RLE Haus 36-428 Joel Yuen The Research Laboratory of Electronics, Massachusetts Institute of Technology [yuen_001] abstract The understanding and control of energy flow at the nanoscale via exciton dynamics is of fundamental chemical and physical interest, but is also technologically relevant for the design of novel light-harvesting materials. In the first part of my talk, I will explain some of our work designing spectroscopic protocols to understand exciton dynamics under coherent illumination via ultrafast Quantum Process Tomography (QPT), a technique which retrieves the time evolution of the quantum state of excitons via nonlinear spectroscopy (1,2). As an application, I will describe the first ultrafast QPT experiment carried out with the Nelson and Bawendi groups at MIT on a nanotubular J-aggregate system at room temperature. I will also clarify the possible relevance of strongly coupled chromophores in natural light-harvesting under incoherent illumination from sunlight (3). Then, I will proceed to explain how one can in principle distinguish excitonic coherences and their vibrational counterparts in nonlinear spectroscopy (4,5). In the last part of my talk, I will describe current work (6) designing topologically nontrivial phases that robustly and selectively move excitons in particular spatial directions of a molecular crystal, simulating solid state "topologically protected" phenomena like the Quantum Hall Effect, which are robust against material imperfections and static disorder. I will end by presenting our most recent work on creating one-way waveguides of plexcitons (strongly coupled excitons and surface-plasmon polaritons). (1) J. Yuen-Zhou, Jacob J. Krich, Masoud Mohseni, and A. Aspuru-Guzik, Quantum state and process tomography of energy transfer systems via ultrafast spectroscopy, Proc. Nat. Acad. Sci. USA. 108, 43, 17615 (2011). (2) J. Yuen-Zhou, D. Arias, D. Eisele, J. J. Krich, C. Steiner, K. A. Nelson, and A. Aspuru. Guzik, Coherent exciton dynamics in supramolecular light-harvesting nanotubes revealed by ultrafast quantum process tomography, ACS Nano 8 (6) 5527 (2014). (3) I. Kassal, J. Yuen-Zhou, and Saleh Rahim-Keshari, Does coherence enhance transport in photosynthesis, J. Phys. Chem. Lett. 4 (3), 362 (2012). (4) J. Yuen-Zhou, Jacob J. Krich, and A. Aspuru-Guzik, A witness for coherent electronic vs vibronic-only oscillations in ultrafast spectroscopy, J. Chem. Phys. 136, 234501 (2012). (5) A. Johnson, J. Yuen-Zhou, A. Aspuru-Guzik, and J. Krich, Practical witness for electronic coherences, J. Chem. Phys. 141, 244109 (2014). (6) J. Yuen-Zhou, S. Saikin, N. Yao, and A. Aspuru-Guzik, Topologically protected excitons in porphyrin thin films, in press, Nature Materials 13, 1026 (2014). bio Joel Yuen-Zhou got his BSc in 2007 from the MIT, where he worked as a UROP with the late Robert J. Silbey, simulating the absorption spectra of light-harvesting antennae in purple bacteria. He then obtained his PhD in 2012 from Harvard under the supervision of Alán Aspuru-Guzik working on various aspects of time-dependent density functional theory, quantum information, and nonlinear spectroscopy. In 2013, he came back to MIT to work at the Center for Excitonics as the Robert J. Silbey postdoctoral fellow, where he got interested in the connections between excitonic systems and topologically nontrivial phases in condensed matter. He will start his own research group in theoretical chemical physics as an assistant professor at the University of California San Diego in the Department of Chemistry and Biochemistry as of July 2015. The Center For Excitonics Is An Energy Frontier Research Center Funded By The U.S. Department Of Energy, Office Of Science And Office Of Basic Energy Sciences Light refreshments

9 years

[Aspuru-Guzik group list] practice talks and final defense

by Ryan Babbush

Hi Group, The final defense of my dissertation will occur this Wednesday at 2pm in the Division Room. The talk will provide an overview of selected topics from my thesis that I hope will be accessible to anybody in the group. As the Division Room is rather small, its possible that not everybody is going to fit. However, I will also be giving two practice talks today and tomorrow and anyone interested is welcome to come! Today I will begin my practice talk at 3pm in the Division Room. Tomorrow I will begin my practice talk at 2:45pm in the Division Room. Best Regards, Ryan

9 years

[Aspuru-Guzik group list] excitonics meeting

by Alan Aspuru-Guzik

Dear group members affiliated with excitonics. We have a thrust meeting at MIT next week. See info below... Looking forward to seeing you there, Alan We’ve reserved Room 220 in Building 16 at 9am on Wednesday 4/22 for this meeting, Keith and Alan, if this time/date doesn’t work please let us know and we’ll try to coordinate an alternative.

9 years

[Aspuru-Guzik group list] Good job

by Alan Aspuru-Guzik

http://www.ccl.net/cca/jobs/joblist/mess0033313.shtml -- Alán Aspuru-Guzik | Professor of Chemistry and Chemical Biology Harvard University | 12 Oxford Street, Room M113 | Cambridge, MA 02138 (617)-384-8188 | http://aspuru.chem.harvard.edu | http://about.me/aspuru

9 years

[Aspuru-Guzik group list] Excitonics

by Alan Aspuru-Guzik

Thank you all for the excitonics blog reports. They look fantastic. Great job. Go ahead and post them. Alan -- Alán Aspuru-Guzik | Professor of Chemistry and Chemical Biology Harvard University | 12 Oxford Street, Room M113 | Cambridge, MA 02138 (617)-384-8188 | http://aspuru.chem.harvard.edu | http://about.me/aspuru

9 years

[Aspuru-Guzik group list] Backpack in Division room

by guerreschi＠fas.harvard.edu

Did anyone forget a black backpack in Division room? On the table near the blackboard… G

9 years

[Aspuru-Guzik group list] [qip] Friday the 17th

by Edward Farhi

Hi Quanta We will meet tomorrow at 11:00 in our usual spot. Our visitor Michael Bremner will give a brief presentation and Scott is in my book to say a few words. Best, Eddie Edward Farhi farhi(a)mit.edu _______________________________________________ qip mailing list qip(a)mit.edu http://mailman.mit.edu/mailman/listinfo/qip

9 years

[Aspuru-Guzik group list] [Aspuru-meetings-list] Group Meeting 4/16, 2:30pm, Div. Room

by Jennifer Wei

Hi everyone, Tomorrow Sam will be giving us group meeting. Please see below for the title and abstract of his talk. Cheers, Jennifer -------------------------------------- Modeling Exciton Dynamics in Biliproteins and Simple Dimers Exciton dynamics of two phycobiliproteins are examined using spectral densities obtained from preliminary QM/MM results and the hierarchical equations of motion (HEOM). We observe that the lowest frequency peak in the spectral density has by far the largest impact on the coherence lifetimes. Cutting down to this single peak allows us to go deep in the hierarchy, at which point coherences are dramatically reduced. This prompted us to examine a simple dimer over a parameter space spanned by more than 150,000 HEOM simulations. A number of interesting trends found in this massive data set are presented. _______________________________________________ Aspuru-meetings-list mailing list Aspuru-meetings-list(a)lists.fas.harvard.edu https://lists.fas.harvard.edu/mailman/listinfo/aspuru-meetings-list

9 years

[Aspuru-Guzik group list] presentation clicker

by Ryan Babbush

Hi group, I am in the process of preparing for my defense and I would like to use a clicker, especially since that pathetic VGI cord in the Division room is five feet too short. The group clicker is a Logitech R800, which does not support Mac (people on the internet says it works sometimes but it definitely doesn't work for me). Accordingly, does anyone else have a presentation clicker I can borrow that does work with Macs? This would be greatly appreciated. Cheers, Ryan

9 years

[Aspuru-Guzik group list] ITAMP lunch seminar (4/17)- Prof. Alex Turbiner

by Singh, Swati

*ITAMP Topical Lunch Discussion* *Date:* Friday, April 17th *Time: *12:00-1:30 pm Pizza will be served. *Location:* B-106 @ Center for Astrophysics (60 Garden Street) *Speaker:* Prof. Alexander Turbiner (Stony Brook and Mexico-City) *Title:* Helium-like Coulomb system: two critical charges, 2nd excited state of H− ion and all that *Abstract: * Reduced Coulomb problem of two electrons in the field of charged fixed center $Z$ $(H^-, He, Li^+, \ldots)$ is discussed and its connection to H2+-ion. Current situation with $1/Z$ expansion is reviewed, numerical deficiencies of seemingly firmly-established results are indicated. First nuclear critical charge (corresponding the zero ionization energy) is recently established with high accuracy (Drake et al, 2014; Olivares-Pilon & AT, 2014)). Second nuclear critical charge (a loss of normalizability of ground state) predicted by Stillinger and Stillinger (1966, 1974) is calculated as well as associated square-root branch point singularity with exponent 3/2. It seems it implies (i) a level crossing $1S-2S$ states and (ii) the existence of a bound state embedded to continuum. It leads to the prediction of the spin-singlet, 2nd excited state of negative hydrogen ion of the same symmetry as the ground state, situated very close to threshold, which looks as an experimental challenge to detect. It is conjectured that for any many-body Coulomb system (atomic or molecular type) there is square-root branch point with exponent 3/2 at critical charge. -- Dr. Swati Singh Institute for Theoretical Atomic, Molecular, and Optical Physics (ITAMP), Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-14, Cambridge, MA 02138 https://www.cfa.harvard.edu/~ssingh/

9 years

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aspuru-list April 2015