Entanglement-based quantum network – sciencedaily

A team of researchers from QuTech in the Netherlands reports the realization of the first multi-node quantum network, connecting three quantum processors. In addition, they performed a proof-of-concept of the main quantum network protocols. Their findings mark an important step towards the future quantum internet and have now been published in Science.

The quantum internet

The power of the Internet lies in the fact that it allows two computers on Earth to be connected to each other, which enables applications unsuspected when it was created decades ago. Today, researchers in many laboratories around the world are working on the development of early versions of a quantum internet – a network that can connect two quantum devices, such as quantum computers or sensors, over great distances. While the internet today distributes information in bits (which can be 0 or 1), a future quantum internet will use quantum bits which can be 0 and 1 at the same time. “A quantum internet will open up a range of innovative applications, ranging from unassailable communication and cloud computing with full user privacy to high-precision timing,” says Matteo Pompili, doctoral student and member of the research team. “And as with the Internet 40 years ago, there are probably many applications that we cannot foresee at the moment.”

Towards ubiquitous connectivity

The first steps towards a quantum internet have been taken over the past decade by connecting two quantum devices sharing a direct physical link. However, being able to transmit quantum information through intermediate nodes (analogous to routers in the classical Internet) is essential to create a scalable quantum network. In addition, many promising quantum internet applications rely on entangled quantum bits, to be distributed among multiple nodes. Entanglement is a phenomenon observed at the quantum scale, fundamentally connecting particles at small and even large distances. It provides quantum computers with their enormous computing power and is the fundamental resource for sharing quantum information on the future quantum Internet. By performing their quantum network in the laboratory, a team of researchers from QuTech – a collaboration between Delft University of Technology and TNO – is the first to have connected two quantum processors via an intermediate node and to have established a tangle shared between several supports. – quantum processors alone.

Harnessing the quantum network

The rudimentary quantum lattice consists of three quantum nodes, some distance apart in the same building. In order for these nodes to function as a true network, researchers had to invent a new architecture that allows scaling beyond a single link. The middle node (called Bob) has a physical connection to the two outer nodes (called Alice and Charlie), allowing entanglement links to be established with each of these nodes. Bob is equipped with an additional quantum bit that can be used as memory, allowing a previously generated quantum link to be stored while a new link is being established. After establishing the Alice-Bob and Bob-Charlie quantum links, a set of quantum operations at Bob converts these links into an Alice-Charlie quantum link. Alternatively, by performing a different set of quantum operations at Bob, the entanglement between the three nodes is established.

Ready for future use

An important feature of the network is that it announces the success of these (inherently probabilistic) protocols with a “flag” signal. Such an announcement is crucial for scalability, because in a future quantum internet, many of these protocols will need to be concatenated. “Once established, we were able to preserve the entangled states that resulted from them, by protecting them from noise,” explains Sophie Hermans, another member of the team. “This means that in principle we can use these states for quantum key distribution, quantum computation, or any subsequent quantum protocol.

Quantum Internet demonstrator

This first entanglement-based quantum network provides researchers with a unique test bed to develop and test quantum hardware, software and Internet protocols. “The future quantum internet will be made up of countless quantum devices and intermediate nodes,” says Ronald Hanson, who led the research team. “QuTech colleagues are already studying future compatibility with existing data infrastructures. In due course, the current proof-of-concept approach will be tested outside the lab on existing telecommunications fiber – on QuTech’s Quantum Internet demonstrator, whose first metro link is expected to be completed in 2022.

Top level layers

In the lab, researchers will focus on adding more quantum bits to their three-node network and adding higher-level software and hardware layers. Pompili: “Once all the high level control and interface layers to run the network have been developed, anyone will be able to write and run a network application without needing to understand how lasers and cryostats work. . This is the end goal. ”

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