Working towards a networked quantum computer, the first milestone is to develop quantum error correction. Quantum error correction is essential for large-scale quantum systems. By encoding a logical quantum bit in multiple physical qubits it becomes possible to detect and correct errors so that the quantum system becomes more stable with increasing size. We have recently demonstrated the first complete cycle of quantum error correction using a 4-qubit diamond processor. In the next years, we aim to realize a logical qubit that is protected against all types of quantum errors. A second milestone is to demonstrate the use of a networked quantum computer to execute a small-scale distributed quantum algorithm.
Working towards a quantum Internet, the five-year objective of the roadmap is a rudimentary multi-node quantum Internet that connects four different cities in the Netherlands. Recently, we passed an important milestone towards this goal: the first “loophole-free Bell test”. In a loophole-free Bell test two remote systems – in our case 1.3 kilometers apart – show correlations that defy any explanation through classical physics. In addition to its fundamental importance for our worldview, this experiment directly distributes an intrinsically secure random key for communication. Importantly, because all loopholes are closed, it is impossible for an eavesdropper to intercept or fake the key without being noticed.
Along the road to a quantum Internet, there are several milestones. The most important is overcoming the inevitable imperfections in the quantum processors and connections through techniques such as quantum repeaters. A quantum repeater is the basic unit needed for extending quantum networks over longer distances. We aim to demonstrate the quantum repeater principle within the next years by connecting two nodes more than 1 km apart via several rounds of entanglement generation and purification.
This roadmap is also the coordinator of The Quantum Internet Alliance (QIA), a collaboration of 23 European partners from academia and industry with the objective of further developing all necessary components of a quantum internet. The aim is to make concrete steps in advancing the technology for realization and market readiness. The project encompasses aspects including end-node hardware, network repeater hardware, quantum network control and applications, integration and blueprint development. More information and news can be found on the QIA website and twitter @eu_ia.