The National Society of Black Physicists (NSBP) is pleased to present Dr. Charles Brown as the next speaker for the NSBP ‘Innovate Seminar Series’! The Innovate Seminar Series is a new forum for NSBP members to share their research ideas and projects in a non-specialist way. Dr. Brown is an experimental quantum physicist, science communicator, and champion for increased Black American representation in physics. He is now a postdoctoral scholar and Ford Foundation fellow at the University of California, Berkeley. Special thanks to the Kavli Institute of Theoretical Physics for their continued support of the NSBP Innovation Seminar Series.
Dr. Charles Brown is an experimental quantum physicist, science communicator, and champion for increased Black American representation in physics. Charles earned his B.S. with honors in physics at the University of Minnesota, Twin Cities. He also earned a Ph.D. in physics at Yale University, where he conducted experiments with superfluid helium-filled optical cavities, and magnetically levitated superfluid helium drops in vacuum. He is now a postdoctoral scholar and Ford Foundation fellow at the University of California, Berkeley. At Berkeley, he is a member of the Ultracold Atomic Physics Group, where he investigates ultracold atoms trapped in optical lattices, which offers an avenue to study a rich variety of many-body quantum physics phenomena. Charles has a long history of both empowering students - spanning the elementary through graduate levels - to pursue their STEM interests, and advocating for the interests of Black students. Charles recently wrote a widely read op-ed about Black underrepresentation in physics that appeared in Physics Today, which has been sparking important conversations regarding necessary changes in the physics community.
Geometric frustration of particle motion in a kagome lattice causes the single-particle band structure to exhibit a dispersion-less, flat band. Generally, frustration can cause a vast degeneracy of low-energy states, and instabilities in the presence of atomic interactions may lead to the manifestation of exotic states of matter. The kagome lattice, a pattern of vertex-sharing triangular plaquettes, offers the highest degree of frustration among two-dimensional lattice geometries. We create an optical kagome lattice by superimposing two optical triangular lattices made from laser light with commensurate wavelengths. We probe the band structure of the kagome lattice by preparing a Bose-Einstein condensate in excited Bloch states of the lattice, and then measuring the atoms’ group velocity via the atomic momentum distribution. We find that atomic interactions renormalize the kagome lattice band structure, significantly increasing the dispersion of the third band, which, according to non-interacting band theory, should be nearly flat (dispersion-less). Measurements at various lattice depths and gas densities agree quantitatively with predictions from the lattice Gross-Pitaevskii equation, which indicates that the observed band structure distortion, onset by atomic interactions, is caused by the distortion of the overall lattice potential away from the kagome geometry.
View the talk below.