New Faculty: Alfred Zong & Jeongwan Haah

Introducing Alfred Zong:

Returning to my alma mater as the newest faculty member in condensed matter physics and ultrafast science is truly a special experience. I was a physics undergraduate and computer science coterm in the class of 2015. Despite the peer pressure and allure of eye-watering paychecks in Silicon Valley, I found my true home in experimental physics. It offers the intellectual stimulation of problem-solving when building one-of-a-kind instruments — similar to what I found in a software engineering team, but with more hands-on creativity.

On a deeper level, it feels incredibly fulfilling, almost viscerally, to be one of the privileged few who get the first chance to observe the beautiful and often unexpected phenomena that mother nature reveals to us. This philosophy carried me through the cold winters at MIT for my Ph.D., and then back to the Bear Territory in the Bay Area for my postdoc. Now, it is time to complete the full circle and share this perspective with my group as we embark on exploring more unknowns together.

My group develops ultrafast “cameras” to capture the nanoscopic world of non-equilibrium states of solid materials, and these movies help guide us to develop strategies for realizing special material properties not typically found in their equilibrium phase diagrams. How fast is “ultrafast”? It depends on the elementary processes we are interested in measuring. In a crystal, lattice ions typically vibrate with a time period of 100 to 1,000 femtoseconds (1 femtosecond = 10 15 second), while electrons, being much lighter, exhibit collective motions on the order of 100 to 1,000 attoseconds (1 attosecond = 10 18 second). To put these numbers in perspective, the age of the universe is about 4×1017 seconds, so we are working at the other extreme end of the observable timescale in physics! Our specialty lies in recording these fast motions in real time, similar to stroboscopic imaging, where a flash of light “freezes” a fast-moving object. In our lab, we also use very short flashes, either an attosecond laser pulse for broadband absorption spectroscopy or a femtosecond electron pulse for diffraction, which make movies of dancing electrons, spins, and ionic lattice.

I am particularly fascinated by two aspects of these ultrafast movies. The first is the spatial heterogeneities that can develop in solids under a non-equilibrium condition, which set phase transitions in solids apart from chemical reactions in molecules. Such heterogeneity can include topological defects, disorder, or spontaneous pattern formation, but most ultrafast tools today lack the resolution to study these nanoscopic and mesoscopic complexities. The second aspect concerns a myriad of coupled degrees of freedom in solids, whose interaction can be leveraged to achieve more controlled dynamical responses and non-equilibrium statets. For example, in two-dimensional magnetic thin films, a sudden change in the spin configuration can induce novel lattice motion relevant to nanomechanical devices. In turn, extreme strains in these film along specific directions can reconfigure the spin order. Deterministic spin control, a challenging subject in ultrafast magnetism, can hence be tackled from the angle of ultrafast strain manipulation.

Just as Oppenheimer found solace on horseback at Perro Caliente, I am a hiking enthusiast with a special attachment to Yosemite, which still tops my list in spite of its touristy feel nowadays. I foresee some of the best physics discussions happening on the scenic drive to the Sierra Nevada or on the way up to Half Dome.

Introducing Jeongwan Haah:

I grew up near the southern end of Korean Peninsula and studied math and physics as an undergraduate at Seoul National University. I graduated from Caltech with PhD in physics, was a Pappalardo Postdoctoral Fellow in Physics at MIT, and then have been a researcher at Microsoft Quantum.

I do theoretical research in the areas of topological phases of many-body systems, their connection to quantum fault tolerance, and algorithms for quantum learning problems. I ask questions of the following flavor: what phases of matter and dynamics are there if we forget much of local details, and what probes do we have for them? What are the best ways to encode quantum information in physical systems where the merit is quantified by the degree of external intervention, tolerance to imperfect controls, and the complexity of logical manipulation. What are the best ways to characterize physical systems and to simulate them on quantum or classical computers? More recent interests include random dynamics, seeking for universal features and developing derandomization methods. I love my profession in part because I can surely say "I'm working" while lying on a couch.

My research is interdisciplinary. I am fascinated by physical phenomena that are discovered through the lens of information, strive to answer ensuing questions with full mathematical rigor, and apply learned intuition to algorithms. Stanford excels in all areas I am currently interested, and, with very high probability, will have experts in topics that I will be interested in. I feel privileged to be able to work with some of the greatest scientists of the present and guide those of the future. I hope my influence will be positive.