Title: A semiconductor-diamond nanophotonic transmitter for long-distance quantum communication
Nontechnical description: Quantum communication is fundamentally secure. Currently, quantum-secure communication distance is limited to less than 100 km by photon absorption in fibers. Theoretically, this limitation can be overcome by a network of quantum repeaters relying on entanglement between communication nodes. The experimental quantum communication community has primarily focused on higher performance metrics for a single device. As a result, proof-of-principle experiments illustrating the potential of quantum technologies for secure communication have been realized utilizing physically large, expensive, and non-scalable technologies at cryogenic temperatures. The critical question remains whether long-distance communication, utilizing quantum repeaters, can be realized in a scalable platform. To reach this goal, this work employs two transformative approaches. First, an integrated hybrid-materials platform that has the potential to realize all device functionalities required for a quantum transmitter is adopted. Second, state-of-the-art computational techniques are utilized to design photonic devices that exhibit unprecedented nonlinear capabilities, enabling the desired performance under the constraints of compatibility with semiconductor fabrication processing. In particular, compact devices are designed to efficiently extract photons emitted by a defect in diamond; the extracted photons are then routed into a nonlinear device that efficiently converts them to telecom wavelengths; finally, the photons are coupled into an optical fiber for low-loss, long-distance propagation. The technologies engineered to reach this goal are expected to also advance the current state of optical information processing and sensing, due to improved nonlinear optical and reconfigurable devices. The diverse team of investigators will train the next generation of photonics engineers in skills including nanophotonic design, nanofabrication, optical spectroscopy, and integrated quantum technologies for tomorrow's optoelectronics industry. Recruitment at all levels, from pre-college to postdoctoral, will have a focus on broadening participation to further integrate women, underrepresented minorities and veterans through direct integration into the scientific team as well as outreach efforts including a proposed EFRI-REM residential program and Science CafÃ©s to engage the investigators? local communities in the fields of optical and quantum communication.
This proposal seeks to realize a photonic integrated circuit for creating and transmitting indistinguishable spin-entangled photons at telecom wavelength. Emission of spin-entangled photons from diamond color centers will be enhanced by a waveguide-coupled resonant plasmonic device, providing an avenue toward operation at elevated temperature. These photons will be spectrally filtered and dynamically routed via an optical switching network to an integrated quantum frequency converter. The resulting telecom-wavelength single photons will be further filtered before off-chip coupling to a fiber-optic cable. The design of the resonant enhancement and nonlinear frequency conversion devices will be performed by a novel inverse-design method based on topology optimization that has only recently become tractable with available computation resources. Several key avenues are identified to mitigate against unavoidable device inhomogeneities and enhance the prospects for scalability. Nonlinear frequency conversion will simultaneously perform frequency conversion and spectral which-path erasure necessary for quantum entanglement. Tunable ring resonators simultaneously provide filtering and routing capabilities. In the short-term, realization of the quantum communication transmitter will require unprecedented integration of quantum optics, nanophotonics, plasmonics, and nonlinear optics. In the long-term, the proposed technology has the potential to enable long-distance, fiber-based, unconditionally secure communication.