CAREER: Electron-phonon processes in gate-defined silicon quantum dots: measurement, control, and applications.

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Non-technical abstract: Acting like electrically controllable ‘artificial atoms’, quantum dots are a useful system to study a wide range of condensed matter physics phenomena ranging from bond formation and magnetism to the fundamentals of quantum information. In this project, the research team will study the ubiquitous coupling between electrons and phonons. Of particular interest is the impact of the phonons on the spin of the electrons. Control over the phonon-spin interaction, achieved here via nano-structuring and applied strain, has crucial implications for a number of applications, such as quantum computing. In the course of this project, a new generation of undergraduate and graduate students are being trained with expertise in nanoscale fabrication, cryogenics, and microwave measurements. These skills are relevant to the nationwide calls for a quantum workforce. The research efforts are being integrated with the Microelectronics Processing course at Mines via development of illustrative quantum experiments. Finally, modules are being developed to be incorporated into outreach efforts to middle school children in the Rocky Mountain Camp for Dyslexic Children.Technical abstract: Electron-phonon coupling is ubiquitous in Condensed Matter systems. It plays a pivotal role in relaxation and decoherence (in case of multiple spins) of electronic spin states and is predicted to mediate many-body phenomena. An immense body of research on tailoring it in fields as varied as superconductivity and thermoelectrics exists. Insight from these fields has never been applied to experiments in few-spin systems. This is a new and impactful opportunity, since few-spin systems are the fundamental prototype for rationalizing spin dynamics in more complex systems, important for quantum information applications. This project bridges the gap via an experimental effort focused on control and measurement of electron-phonon processes in silicon gate-defined quantum dots. The phonon bath is engineered through nano-structuring and spin-orbit coupling is controlled via applied strain to investigate the theoretically predicted ‘protected’ states. Measurements of spin relaxation and decoherence time are performed. Controlling the coupling of spins to the phonon bath has profound implications. First, it can be used for the design of ‘hot’ qubits and spintronic devices. Second, it leads to an examination of hitherto untested theoretical predictions. Third, the novel protocols developed in the project for sensing nanoscale electron-phonon thermalization are foundational for future quantum thermodynamics studies on the quantum dot platform. Finally, this is a pioneering effort to apply insight from the vast field of nano-phononics to spin qubits and paves the way for future integration of the fields.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.