NSF-BSF: Optical Coherent Control of Quantum Dot Spin for Ultra-Fast Quantum Information Processing

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Among the many choices for solid-state quantum emitters, indium arsenide quantum dots exhibit some of the best optical properties. They emit photons with nearly perfect efficiency and purity. In addition, quantum dots can trap single electrons that act as quantum memories that strongly interact with photons, a key ingredient for long-distance quantum networks. But these spins lose their quantum properties extremely fast because they interact with a large number of nuclear spins that always exist in the natural crystalline structure of the host substrate. In order to improve the quantum properties of these spins and increase the timescales over which they persist requires a better fundamental understanding of spin-nuclear interactions in semiconductors. This improved understanding could directly enable methods to decouple the electrons from the large nuclear spin bath, resulting in orders of magnitude improvements in their coherence lifetime. This program aims to both attain a better understanding of spin nuclear interactions and improve spin lifetimes in semiconductors using a technique called dynamical coherent control. This approach manipulates the spin rapidly to decouple it from noise sources on different timescales. Using this technique, the principal investigator will study the noise properties of spins in a semiconductor host material, and develop new techniques to eliminate them. Success of this program could enable a new generation of chip-integrated quantum devices that can efficiently store and transmit quantum information over long distances. This program is a collaborative NSF-BSF proposal which combines the expertise of the University of Maryland in quantum dot spectroscopy and the Hebrew University in Jerusalem on noise spectroscopy and coherent spin control.To achieve the program goals, the collaborative team will combine state-of-the-art noise spectroscopy and dynamical decoupling with nanophotonic engineering. They will develop a novel optical excitation scheme based on ultra-fast modulation of a narrowband laser to achieve complete spin control along all three axes. Such modulation can be programmed to create nearly unlimited control sequences, thus enabling spin control with significantly greater complexity and opening new possibilities for quantum information processing. They will use this new scheme to perform noise spectroscopy of the quantum dot spin qubit, elucidating the physics underlying its dominant noise sources. Using the physical insight gained from these experiments, they will develop optimized dynamical decoupling sequences that could significantly extend the coherence time of the qubit beyond current state-of-the-art. Coupling these optically active quantum memories to nanophotonic cavities will provide a path to engineer efficient spin-photon interfaces, and achieve large scalability. The ability to control and decouple nuclear spin interactions in III-V semiconductors would provide a qubit system with long-lived coherence properties and nearly pristine quantum emission. Such a system could form the fundamental building block for quantum networks, photonic quantum computers, and quantum sensors. In the III-V semiconductor community, spin dynamics remains a poorly understood area of research with many open questions regarding the dominant noise interactions and fundamental coherence limits. This research will shed light on this poorly understood physics, opening up brand new applications and control tools for spin in III-V semiconductor materials. In addition to the research component, this program will include a strong outreach effort to educate high school students and broaden participation in STEM 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.