CAREER: Quantum Hydrodynamics: From Electron Fluids To Chiral Active Matter

Cuny City College, New York NY

Investigators

Abstract

NONTECHNICAL SUMMARY This career award supports research and education on the collective properties quantum mechanical fluids and active matter systems. The study of quantum mechanical phenomena on the mesoscopic scale, intermediate between the macroscope and the scales of atoms, holds promise to advance understanding of how the unusual quantum world connects with the familiar macroscopic world and may lead to new electronic device technologies. Robust quantum effects can manifest at sufficiently low temperatures where essentially the whole system can behave like a single quantum mechanical entity that can exhibit unusual and counterintuitive properties. Superconductivity is one example of such a quantum state of matter. The electrons in superconducting states behave like fluids that can flow without viscosity and so, without dissipation, a phenomenon not displayed by the classical fluids of everyday experience. Theoretical understanding of quantum fluids is built on hydrodynamics, which is the theory of classical fluid motion under external forces. The PI and his research team will focus on developing theoretical descriptions of such states as modifications of the classical hydrodynamics in a conceptually transparent way that captures the unique properties of the macroscopic quantum state. The PI’s effort in this direction will build toward generalizing the approach for other quantum liquids, including those that arise in electrons that are trapped between two semiconductor layers and exposed to a perpendicular magnetic field, quantum Hall fluids. Success of this long-term objective will hopefully uncover hitherto untapped mesoscale phenomena that can be harnessed to develop the technology of a new generation of quantum devices. Inspired by the appearance of dissipation-free phenomena analogous to quantum fluids, the PI will investigate fluids made of self-propelled particles that can autonomously change direction as they move. These chiral active matter systems obey the laws of classical mechanics but are far from the tranquil state of equilibrium. The PI aims to investigate the extent to which they may be able to serve as simulators of quantum fluids. An important component of this project is to disseminate the research effort via three channels of education and training (a) a special topics course on fluid dynamics applied to condensed matter systems aimed at graduate students and senior undergraduates, (b) Research opportunities for undergraduates and high school students, and (c) Interactive demonstrations based lectures for high school students on basic fluid dynamics principles that underpin the research effort. This component will seek to remedy the resource scarcity for setting up demonstrations in many of the schools under the ambit of the College-Now program run at City College of New York. TECHNICAL SUMMARY This career award supports research and education on the collective properties of mesoscopic quantum systems and chiral active matter systems. Understanding the transport properties of ground-state quantum fluids such as superconductors and Quantum Hall (QH) fluids is not only important for fundamental physics but also central to the development of the next generation of low dissipation electronic devices. In this project, the PI and his research team will investigate the quantum modifications to classical hydrodynamics that arise beyond the ideal fluid regime due to dominant non-linear and higher gradient viscous effects. The non-linear nature of the theory facilitates the study of the strong interaction effects of quantum many-body systems. The PI will focus on three interrelated objectives that share a common quantum hydrodynamic framework: (I) Study the phenomenology of QH hydrodynamics that includes higher gradient effects such as odd/Hall viscosity: Developing a hydrodynamical theory of QH fluids that includes higher gradient odd viscous effects will bring new insight into the fluid nature of QH state in the form of non-linear effects and free surface dynamics which has so far remained outside analysis based on topological field theories. (II) Incorporate non-linear fluid dynamical effects in the transport properties in viscous electron fluids: The proposed research in viscous electron fluids will enable the study of non-linear effects, such as solitons, in mesoscopic transport. This research direction is timely due to the recent experimental advances in mesoscopic quantum systems such as Gallium Arsenide and Graphene, which are host to viscous electron fluids. (III) Determine the mechanical properties and hydrodynamic instabilities of non-equilibrium chiral active fluids: Chiral active fluids despite being non-equilibrium classical systems, share many properties with QH fluids and viscous electron fluids and can serve as analog simulators. Understanding the mechanical response and instabilities of chiral active matter will not only help design active matter experiments that can be used to understand quantum fluids but can also lead to the design of new synthetic active materials with remarkable properties. The PI’s long-term effort to develop the semiclassical theory of QH fluids will hopefully bring new understanding in the development of the semiclassical theory of general quantum fluids, which has been a long open problem. The educational objectives of this project will be achieved via three main vehicles: 1) A topical course on fluid dynamics applicable to condensed matter systems for graduate and senior undergraduate students that will be offered at the City College of New York. 2) Research opportunities in the field of theoretical fluid dynamics applied to condensed matter systems for City College of New York undergraduate students and High School for Math Science and Engineering high school students. 3) Interactive and demonstration-based talks on fluid dynamics for New York City high school students in collaboration with the College-Now program, which serves students from inner-city schools and underrepresented groups to facilitate a smooth transition from school to the first years of college. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.