The objective of this program is to investigate how fast photons can be generated successively and deterministically, down to the single-photon level and up at a terahertz rate, in semiconductor quantum dots.
The intellectual merit is to advance the single-photon generation rate from semiconductor materials up by at least 3 orders of magnitude into the terahertz regime. The extremely short radiative lifetime can also allow indistinguishable photons to be robustly generated. Together with the choice of wide-bandgap semiconductor quantum dot materials, it is expected to realize the above goals at a liquid nitrogen temperature and above, which is transformative in the field of semiconductor optics. Successful conclusion of this project will provide critical resources for quantum cryptography and quantum information processing applications, and may open up a new opportunity for optical interconnect at an extremely high speed and requiring only a sub-atto joule of switching energy.
The broader impacts are the advancements of materials science, synthesis, device physics, quantum optics, and many-body physics in the context of ultrafast dynamics of single-photon generation in semiconductor materials and the education components. The results can be far reaching and impact energy-efficient communication network, optical interconnect on the chip, and solid-state lighting. The education plan focuses on outreach and diversity programs aiming to engage K-12 students for physical and engineering science. It also includes curriculum developments on solid-state lighting and multidisciplinary projects for undergraduate students.
In tomorrow’s world, vast amount of information needs to be communicated efficiently and securely, whether across a computer chip or a continent. Photon is a proven information carrier owing to its efficiency and capacity. The quantum nature of photons has been exploited for secure communication and quantum information processing. Efficient switching of light at a single-photon level can ultimately achieve a sub-atto joule switching energy requirement for the information exchange, both classically and quantum mechanically. The ability to efficiently generate, process, and receive information at a single photon level is therefore the ultimate goal for a secure and energy efficient information delivery. This project investigated semiconductor quantum dot structures that are suitable for the above purpose. It has been established in the past that semiconductor quantum dots are potential candidates for efficient single photon generation. However, the rate at which these photons are generated is typically on the order of 1 GHz or slower. To increase the data bandwidth, the quantum dot must be capable of generating photons at a much higher speed. Once approach is to leverage the quantum dot-cavity coupling. Intellectual Merits: This research explored methods to increase the single-photon generation rate from semiconductor materials for 3 orders of magnitude into the terahertz regime. The extremely short radiative lifetime, if shorter than the exciton dephasing time, can allow one to robustly generate indistinguishable photons. Together with the choice of wide-bandgap semiconductor quantum dot materials (indium gallium nitride (InGaN) in this project), we expect to realize the above goals at a liquid nitrogen temperature or above, which is unprecedented (in terms of indistinguishable and ultrafast photon generation) in semiconductor materials. In this project, InGaN quantum dots were coupled to localized surface plasmon resonances in noble metals. Theoretical and experimental efforts have confirmed that such coupling can lead to enhanced spontaneous emission. The average Purcell factor, which measures the enhancement factor of the spontaneous emission rate, was measured to be 46 from a closed-top structure. In an alternative design with an open-top structure, a Purcell factor exceeding 1000 has also been predicted theoretically while maintaining a reasonable device efficiency for practical applications. Broader Impacts: The scientific impacts of this project include the advancements of materials science, synthesis, device physics, quantum optics, and many-body physics in the context of ultrafast dynamics of single-photon generation in semiconductor materials. The results are far-reaching and have positive impacts on society and national security including but not limited to energy-efficient communication network, optical interconnect on the chip, solid-state lighting, and quantum information processing. Through the developments of nitride semiconductor single-photon emitters, we have gained comprehensive understanding of the optical properties of InGaN quantum dots which are still relatively unexplored owing to the difficulties of obtaining high quality and small-sized (< 10 nanometers) dots. Our education activities focused on outreach and diversity programs aiming to engage K-12 students for physical and engineering science while we continued to incorporate research findings into the existing courses and developed a new course in solid-state lighting that is of critical importance in future energy conservation.
