Many-body Physics with Electrons on Helium

Non-Technical Abstract: Low-dimensional electron systems play an important role in modern condensed-matter physics and quantum information science (QIS). A uniquely clean and well-controlled example is provided by electrons trapped on the surface of superfluid helium. In this system, electrons float in vacuum just above the helium surface at temperatures near absolute zero, where the helium is superfluid. The absence of disorder and defects makes electrons on helium the most pristine two-dimensional electron system known and a paradigm for quantum information science many-body systems. Because of its exceptional properties, electrons on helium provide a ideal platform for exploring collective quantum behavior that is difficult or impossible to study in conventional materials. The interactions between electrons can be tuned by controlling their spacing, while their coupling to excitations of the helium surface can also be experimentally controlled. This allows direct investigation of how different types of interactions shape the behavior of quantum many-particle systems. The proposed research will use this platform to study new collective effects in low-dimensional systems and to build analogues of problems in QIS, including models of how electron qubits interact with lattice vibrations in solids. Such interactions are central to many technologies in quantum sensing and quantum information but are difficult to tune in real materials. In addition to advancing fundamental understanding, this work provides a powerful setting for training students at the intersection of experiment, theory, and quantum information science. Technical Abstract: The goal of this joint theoretical and experimental effort is to understand the many-body quantum physics of electrons on helium and how it informs the understanding of other condensed matter and quantum information science systems, particularly in the solid state. The richness of the system comes from the interplay of the long-range electron-electron interaction and the electron coupling to the quantum field of excitations in liquid helium. The theoretical and experimental work will (i) use single electrons on helium in quantum dots to emulate the physics of synthetic color centers by implementing a tunable polaronic coupling; (ii) investigate the high-frequency dynamics of the two-dimensional Wigner crystal; (iii) perform and theoretically model unprecedentedly high-frequency transport measurements of electrons on helium to investigate the nature of non-equilibrium melting of the Wigner crystal state and use single-electron devices to explore the microscopic nature of the giant nonlinearity of the electron mobility in this electronic crystalline phase; (iv) investigate the spin dynamics and spin-dependent transport of electrons on helium using microchannel devices integrated with micromagnet “spin-filters”. 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.