Heralded Entangled Sources for All-optical Quantum Networks with a Quantum Advantage

Today, entangled correlations are at the heart of the Quantum 2.0 revolution with the potential to significantly impact the fields of communications, sensing, and computing. In particular, entangled states power fundamentally secure—or “unhackable”—quantum communication. Quantum systems are extremely sensitive to loss and errors, and it is a major unsolved challenge to build a quantum network that can efficiently distribute entanglement that is useful for Quantum 2.0 applications. Existing approaches to quantum networking all face major technological barriers that make them unsuitable for quantum communication. This project will demonstrate a new type of quantum network based on entangled single photons. The networking scheme is based on existing technology, and the tools required to build it are available today. The network will be used to distribute entangled photons to separate users at two different network nodes. Even though the photons will experience high amounts of loss over the network, the distributed entanglement will be subject to negligible error, measured with high efficiency, and distributed at high bit rates—all necessary criteria for secure quantum communications. The network is scalable, meaning more network nodes can be added to allow secure communication between multiple users simultaneously. The proposed system has important implications for privacy and national security. This program will support the training of two graduate students in experimental single photon source design and measurement, and in quantum information and communications theory. The network can be used as an advanced quantum networking testbed that can be used as both an education and training tool, and it will be expanded and maintained in part by high school and undergraduate interns recruited via a new summer program. Distributing high-quality entanglement over lossy channels in a scalable manner is an unsolved problem. The goals of this project are to develop identical sources of path-entangled single photons operating at MHz rates, and to demonstrate entanglement swapping between two sources separated by a 2 km public fiber network. The resulting distributed entanglement can be used to carry out advanced quantum communications protocols that have a provable quantum advantage. A research fiber network connects the NIST and CU Boulder campuses, and this will be used to distribute 99% fidelity entangled states between the two campuses at kHz rates. This approach is scalable, Quantum 2.0 ready, and will for the first time demonstrate a provable quantum communications advantage across lossy, kilometer-scale network links at rates five orders of magnitude higher than current state-of-the-art networking demonstrations. This will lay the groundwork for small-to-medium sized multi-node quantum networks that can be built within the next five years that are capable of distributing larger classes of entangled states. 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.