Developing a tunable single-spin bit for scalable spin-based optoelectronics

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Electronic and photonic devices that operate at the quantum limit will enable many new technologies, including ultrafast photonic switches, fundamentally secure communication, and quantum information processing. Efforts to engineer single-spin optoelectronic devices based on single quantum dots have faced significant challenges because ensembles of quantum dots always have a large inhomogeneous distribution in energy levels. The distribution in energy levels prevents spin bits based on single quantum dots from being integrated into multi-bit devices where each bit must be tuned into resonance with a discrete number of fixed laser or optical cavity wavelengths. Recent discoveries have demonstrated that quantum dot molecules have optical transitions whose wavelength can be tuned in situ over a range ten times larger than available in present single-spin bit designs. Moreover, these quantum dot molecules have other tunable optoelectronic and spin properties that can be engineered at the single-spin quantum level. This program supports development of a prototype bit, based on quantum dot molecules, that can isolate and control a single spin. Coherent and time-resolved magneto-optical techniques will be used to develop and demonstrate operation of this prototype bit and quantify the wavelength tunability that can be achieved. The results will provide a direct path to the production of scalable spin-based optoelectronic devices. Intellectual MeritSingle quantum dots are being actively pursued for integration into photonic and spin-based optoelectronic devices, but the inhomogeneous distribution of energy levels in ensembles of single quantum dots provides a fundamental barrier to scalability. This limitation can be overcome with the proposed new single-spin bit design based on quantum dot molecules. The key element of the proposed bit architecture is the use of indirect optical transitions whose wavelength is an order of magnitude more sensitive to applied electric field than the transitions of single quantum dots. Experiments have shown that these indirect transitions can have dipole matrix elements only a few times weaker than direct transitions. Spin initialization, manipulation and readout methods that utilize the indirect transitions will be developed. The range of wavelength tunability that can be achieved while maintaining spin initialization and readout will be measured. The bit design and spin-control protocols take advantage of recently discovered tunable spin interactions in quantum dot molecules to eliminate the need for transverse magnetic fields and incorporate nondestructive readout. The proposed work will develop and demonstrate a spin-bit design with at least an order of magnitude more wavelength tunability than existing spin-bit designs and consequently eliminate one of the largest obstacles to the scalable production of single-spin-based optoelectronic devices. Broader ImpactsThe proposed work will enrich new courses already under development and provide crucial training for graduate students who will lead the next generation of electronic and photonic device research. The work will further broaden the exposure and opportunities for undergraduates and teacher-scholars participating in summer research programs. Funds from this program will provide local K-12 teachers with equipment to bring cutting-edge scientific concepts into their classrooms and inspire the next generation of students to pursue careers in STEM fields.