Researchers Collaborate on Testbeds to Advance Quantum Internet
Researchers are working to develop a "quantum internet"—the internet of the future that is expected to have capability and security far beyond what is possible today. To advance this research, testbeds to support rigorous, transparent, and replicable testing of scientific theories, computational tools, and new technologies have been established at the University of Arizona (UA) and the Massachusetts Institute of Technology (MIT). These initiatives are supported by the NSF-funded Center for Quantum Networks (CQN), which is headquartered at UA.
The quantum internet is a network that will allow quantum devices to exchange information within an environment that harnesses the laws of quantum mechanics, offering unprecedented capabilities that are impossible to carry out with today's web applications. CQN brings together experts with diverse backgrounds to develop theoretical research and essential devices, components, and systems to realize the vision of a scalable quantum internet. The quantum internet will transmit information encoded in the quantum states of physical objects called "qubits."When two qubits interact and become entangled, any change to one particle in the pair will result in changes to the other so that the state of the first qubit can be "read" by looking at the behavior of its entangled counterpart. CQN's vision is to develop prototype devices, repeaters, and network architectures to support sending 10 million qubits of information per second between multiple locations while serving multiple applications at the same time. CQN's research focus is on building a quantum communication infrastructure supported by fault-tolerant quantum repeaters and routers. The Tucson Testbed provides a place to test silicon photonic chips with various integrated functionalities, demonstrate entanglement distribution with ever-increasing levels of performance, and test resource allocation and management protocols developed in the project. The Boston Testbed focuses on building a quantum repeater system based on fault-tolerant quantum memories in repeater and switching configurations, with the target of achieving high fidelity at a high rate of entanglement distribution.
The CQN teams have made substantial progress toward meeting overall testbed milestones. The Boston Testbed is nearing demonstration of quantum-memory assisted measurement-device-independent quantum key distribution on the MIT-Lincoln Laboratory (MIT-LL) CQN testbed over a 43-km fiber-optic cable. Demonstration of >300-microsecond scale spin coherence in tin-vacancy color centers at 2°K is a highlight, substantiating a robust path to suitable quantum memories well above the 100 mK temperature currently required for silicon-vacancy (SiV) quantum memories. The team has also demonstrated a vertically-loaded diamond microdisk resonator for high- efficiency photon coupling from color centers, which is a critical building block to designing repeaters.
The Tucson Testbed team has set up optical fiber links connecting ten laboratory sites among six buildings across the UA campus, making use of an existing entangled photon distribution network connected by fiber deployed among five of the buildings. Initial characterizations of SiV quantum memory devices have been completed. Entanglement distribution has been demonstrated across campus between the Optical Sciences Center and Electrical and Computer Engineering buildings. Two important highlights of the Tucson Testbed are the experimental demonstrations of pre-shared entanglement improving classical data communications beyond what is otherwise allowed by the laws of physics, and exploiting entanglement and embedded optical-quantum-domain machine learning to improve sensor-network performance.
The repeaters developed in the Boston Testbed will be used by the Tucson Testbed to demonstrate a larger, higher-bandwidth quantum network consisting of repeaters and 42 km of fiber from MIT-LL. This network will demonstrate the effectiveness of the repeaters using a 1Mbit/sec quantum key distribution experiment.
