Stanford Community Health Alerts
The department hosts informal & informational lunches with faculty & several students. There is no set agenda during the discussion and it is completely informal. Students are encouraged to share their experience within the department, research, their plans, and feedback.
Registration is required.
Sign up as soon as you can because the roundtable discussion session is very popular and fills up quickly! Space is limited; you will receive a confirmation email if you are confirmed to attend. Please contact Tiffany, Student Life Coordinator if you have any questions, email@example.com. Thank you!
The student/faculty roundtable discussions are organized by the Student Life Committee.
Millisecond pulsars are rapidly rotating neutron stars with phenomenal rotational stability. The NANOGrav collaboration monitors an array of about 80 of these cosmic clocks in order to detect perturbations due to gravitational waves at nanohertz frequencies. These gravitational waves will most likely result from an ensemble of supermassive black hole binaries. Their detection and subsequent study will offer unique insights into galaxy growth and evolution over cosmic time. I will present our most recent dataset and the results of our gravitational wave analysis, which suggests the presence of a common spectral signature in the data that could be the first hints of a gravitational wave background. I will then describe the gains in sensitivity that are expected from additional data, discoveries of millisecond pulsars, more sensitive instrumentation, and international collaboration and discuss prospects for detection in the next several years.
Ultracold atoms offer a unique platform to study spin physics. When atoms are arranged in an optical lattice in form of a Mott insulator, the atomic motion is frozen out and the study and control of the spin degree of freedom emerges as a new frontier. Heisenberg spin models, where only neighboring spins interact, are the paradigmatic model for many interesting phenomena. Until very recently, all experimental studies with cold atoms addressed the special case of an isotropic Heisenberg model. Using lithium-7 atoms and Feshbach resonances to tune the interactions, we have created spin ½ Heisenberg models with adjustable anisotropy, including the special XX-model which can be exactly solved by mapping it to non-interacting fermions. Spin transport changes from ballistic to diffusive depending on the anisotropy. For transverse spin patterns, we have found several new dephasing mechanisms related to a superexchange induced effective magnetic field. Using rubidium atoms and two atoms per site, we have realized spin 1 models. The onsite interactions give rise to a so-called-single-ion anisotropy term proportional to (S_z)^2, which plays an important role in stabilizing magnetism for low-dimensional magnetic materials. Our studies of spin dynamics illustrate the role of ultracold atoms as a quantum simulator for materials and for elucidating fundamental aspects of many-body physics.
For 130 years, a cylinder made of a platinum-iridium alloy stored near Paris was the official definition of a kilogram, the basic unit of mass. This all changed on May 20, 2019: a kilogram is now defined by a fundamental constant of nature known as the Planck constant h, which relates the energy of a photon to its frequency: h= 6.62607015 10-34 kilograms times square meters per second.
Sounds complicated? In this talk, I will provide the reasons for changing the definition of the kilogram, give simple explanations what the new kilogram is conceptually, and explain how objects with exactly known masses can be realized using advanced technology.
We are excited to announce that our distinguished speaker is Prof. Wolfgang Ketterle, the John D. MacArthur Professor of Physics at the Massachusetts Institute of Technology. Prof. Ketterle works on experimental research in atomic physics and laser spectroscopy and focuses currently on Bose-Einstein condensation in dilute atomic gases. He was among the first scientists to observe this phenomenon in 1995, and realized the first atom laser in 1997. His earlier research was in molecular spectroscopy and combustion diagnostics.
Prof. Ketterle's awards include the Rabi Prize of the American Physical Society (1997), the Gustav-Hertz Prize of the German Physical Society (1997), the Discover Magazine Award for Technological Innovation (1998), the Fritz London Prize in Low Temperature Physics (1999), the Dannie-Heineman Prize of the Academy of Sciences, Göttingen, Germany (1999), the Benjamin Franklin Medal in Physics (2000), and the Nobel Prize in Physics (2001, together with E.A. Cornell and C.E. Wieman).
Prof. Ketterle will also give the Applied Physics/Physics colloquium at 4:30 PM on Tuesday, April 13, 2021. Detailed information about both lectures and our speaker can be found on Physics site (link below). As in previous years, both lectures are free and open to the public via Zoom webinar.
Ion trap quantum computers at first glance have no materials challenges. Ions are all the same by nature and they are trapped and manipulated by electromagnetic fields. The materials challenges arise in how these fields are delivered to the ions. In this talk, I will describe how ion trap quantum computers work and then review the materials challenges that were recently described in Nature Reviews Materials (https://doi.org/10.1038/s41578-021-00292-1).
This presentation focuses on the discovery of memory effect in 2D atomically-thin nanomaterials towards greater scientific understanding and advanced engineering applications. Non- volatile memory devices based on 2D materials are an application of defects and is a rapidly advancing field with rich physics that can be attributed to vacancies combined with metal adsorption. In particular the talk will highlight our pioneering work on monolayer memory (atomristors) that has expanded to over a dozen 2D sheets and can enable various applications including zero-power devices, non-volatile RF switches, and memristors for neuromorphic computing. Much of these research achievements have been published in nature, advanced materials, IEEE, and ACS journals.
 R. Ge, X. Wu, L. Liang, ..., J. C. Lee, and D. Akinwande, "A Library of Atomically Thin 2D Materials Featuring the Conductive-Point Resistive Switching Phenomenon," Advanced Materials, vol. 33, 2021.
 S. M. Hus, R. Ge, P.-A. Chen, L. Liang, G. E. Donnelly, W. Ko, F. Huang, M.-H. Chiang, A.-P. Li, and D. Akinwande, "Observation of single-defect memristor in an MoS2 atomic sheet," Nature Nano., 11/2020.
 M. Kim, E. Pallechi, R. Ge, X. Wu, G. Ducournau, J. Lee, H. Happy, and D. Akinwande, "Analogue Switches made from h-BN Monolayers for 5G and Terahertz Communication Systems," Nature Electronic, 2020.
 S. Chen, M. R. Mahmoodi, ... D. Akinwande, D. B. Strukov, and M. Lanza, "Wafer-scale integration of two-dimensional materials in high-density memristive crossbar arrays for artificial neural networks," Nature Electronics, 10/2020.
 D. Akinwande, C. Huyghebaert, C.-H. Wang, Serna, S. Goossens, L. Li, H. S. P. Wong, and F. Koppens, "Graphene and 2D Materials for Silicon Technology," Nature, 2019.
In the 1970s, Hawking showed that black holes, like any finite-temperature system, radiate energy and so eventually evaporate away entirely. However, his calculations showed something very weird: unlike any other physical system, the radiation seemed to contain no information about the initial state of the black hole. Instead the information that fell into the black hole was simply lost forever. This contradiction between Hawking's calculations and the ordinary rules of quantum mechanics has been a driving force behind much of the research in quantum gravity over the ensuing decades. Finally, in the last couple of years, we have begun to understand where Hawking's calculation went wrong, and to derive precise predictions, consistent with unitary quantum mechanics, for the information content of Hawking radiation. However, the new calculations, which involve weird spacetime topologies called 'spacetime wormholes', lead to as many new questions as answers.