High Quantum Efficiency Uni-Traveling-Carrier Photodiode for Optical to Microwave Transduction

Modern quantum information systems employ optical photons for long distance communication, operating at ambient temperature, between microwave cavities, which house microwave photons used in quantum computing and microwave detection. These optical photons, carried by fiber-optic or free-space links, offer a low-cost, uncooled alternative to bulky, expensive microwave coaxial cables, which are lossy, susceptible to electromagnetic interference, and a significant thermal conductor to the outside ambient environment. To convert between these two types of photons and implement these optical interconnects, it becomes necessary to develop a high-performance photodetector for optical to microwave transduction. Applications of these photodetectors include not only in quantum computing and axion detection, but also in other optical-cryogenic interconnect applications. In this program, a high quantum efficiency, high speed photodetector is proposed, based on previous, successful work with uni-traveling carrier photodetectors. Uni-traveling carrier photodetectors eliminate the slow hole from the drift layer, allowing for higher speeds than their p-i-n counterparts. Both the small business and partnering research institution have demonstrated impressively high-power, high-speed devices, and have a history of successful collaboration in previous government-funded programs. These programs will be leveraged to further optimize for photodetectors which operate at speeds above 5 GHz with quantum efficiencies above 95%. In Phase I, photodetectors will be designed, fabricated, and characterized for device quality, quantum efficiency, and bandwidth. Devices will be demonstrated and delivered to the Department of Energy customer. Risk is mitigated in this Phase I effort through a history of design experience in optimizing device performance, several successful fabrication runs with uni-traveling carrier photodiodes in the proposed materials system, and verified, high accuracy testing equipment and experience at both the small business and partnering research institution. A combination high-speed, high quantum efficiency photodiode which transduces optical to microwave frequencies has numerous applications relevant to a broad spectrum of industries and government entities. For one, providing this frequency down-conversion would solve half of the problem of transducing between optical and microwave photons. This technology could be implemented in the search for the axion, or axion-like particles. A high-quality transducer could also provide a gateway for quantum entanglement between microwave photons at long range or helping to form quantum networks for communication between superconducting quantum computers. Applications span even out to quantum communication and cryptography, allowing for more secure communication between entities, with clear advantages with respect to national security. Critical commercial applications span any fields which necessitate optical-cryogenic interconnects, including radio and infrared astronomy.