Quantum computers promise the next great technology leap. At the heart of a quantum computer are material implementations of quantum bits - qubits - which in the present form are highly sensitive to the environment and are typically only achieved at very low temperatures. This project aims to discover a new type of material that may enable room-temperature quantum computing. The new method is based on electrons and their associated vacancies, also known as holes, in a solid material. When an electron lingers close to a hole, the electrical attraction between the pair leads to the formation of a quantum particle known as an exciton. This project explores the utilization of excitons as qubits for enabling quantum logic devices. Recent studies suggest that excitons may be formed above room temperature in a new type of material known as a topological insulator. The principal investigators use a variety of experimental techniques to understand the nature of excitons in topological insulators, and improve the critical temperature for achieving them, so that they may be sustained at room temperature. This project educates and trains undergraduate and graduate students in the important and rapidly advancing research area of quantum computation, and offers outreach activities targeting K-12 students from underrepresented minority groups.
Topological exciton condensation is a fundamentally new concept which may open an unexplored and exciting research area. Our recent experimental studies of three-dimensional topological insulators have revealed unusual non-local photocurrent at liquid nitrogen temperature, indicating a superfluid-like topological exciton condensate. This project builds on these exciting preliminary results and aims to obtain fundamental understanding of topological exciton condensates. Experiments to unambiguously distinguish the free Fermion and exciton mechanisms by conducting electric field dependent photocurrent mapping are performed. Spatially resolved angle-resolved photoemission spectroscopy (micro-ARPES) supports this effort by characterizing the occupied single-particle spectrum of materials platforms where signatures of an excitonic condensate are observed. Ultrafast spectroscopy is carried out to measure exciton lifetime and velocity. The exciton induced spin polarization is explored using Kerr rotation. An even higher onset temperature for exciton condensation is achieved in thinner and more intrinsic samples and other low dimensional topological materials beyond Bi2Se3. The topological exciton condensate, a high-temperature macroscopic quantum state with long coherence lengths and unique spin texture, has a truly promising potential to be implemented in room-temperature quantum computers.
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.
