Is a universal quantum network possible?

German scientists say for the first time it has been possible to create an elementary quantum network based on interfaces between single atoms and photons.

German scientists say for the first time it has been possible to create an elementary quantum network based on interfaces between single atoms and photons.

Communications networks are vital for our daily lives, and as we attempt to develop high-functioning computing, cloud platforms and machines capable of coping with Big Data, it is also necessary to insure our communication facilities are advanced enough to keep up with these developments.

Led by Professor Gerhard Rempe of the Max Planck Institute of Quantum Optics (MPQ), a team of researchers have created a network consisting of two nodes, each of which can send, receive and store information -- communicating through a single photon traveling along a fiberoptic cable with a length of 60 meters.

Quantum bits, or qubits, are the core of quantum information technologies. Normally, a quantum bit can store one of two values -- 0 or 1. However, there is an intrinsic indeterminacy in quantum mechanics, where a qubit can hover between these two values -- adding a layer of complexity to this block-standard information.

Due to this, quantum computing could not only be equipped with capabilities far beyond our highest-functioning computers at present, but this would boost encryption protocols -- an issue that is becoming more urgent in terms of cyberattacks.

In the prototype model, single rubidium atoms were embedded in optical cavities created by placing two highly reflecting mirrors very closely together. Once a photon enters the cavity, it is reflected between the mirrors thousands of times, which enhances the atom-photon interaction capabilities of the network.

Once the atom passed through, it is captured for a fixed duration of time in the cavity by using laser beam technology. The final stage is to control the emission of single photons emitted from the trapped atom; which allowed the scientists to transfer any stored information from singular photons after a fixed period in a controlled manner.

Quantum information is extremely fragile, and to prevent the loss of information, every component of the quantum network has to be rigidly controlled. It is this method which solves an inherent problem in quantum mechanics -- whilst photos work well to transmit quantum states, they are notoriously difficult to control and store. Therefore, atoms can be used to store qubits, whilst the photons can transmit quantum states.

"We try to build a system where the network node is universal," Ritter told Scientific American. "It's not only capable of sending or receiving--ideally, it would do all of the things you could imagine."

As each node on the prototype can fulfil different functions, including the sending, receiving and storing of information -- it is theoretically possible to scale up the network by connecting additional nodes.

It was also possible to entangle the atoms, which allowed the exchange of information with each other with no distance limitations.

"We have realized the first prototype of a quantum network," Ritter said.

"We achieve reversible exchange of quantum information between the nodes [...] we can generate remote entanglement between the two nodes and keep it for about 100 microseconds, whereas the generation of the entanglement takes only about one microsecond.

Entanglement of two systems separated by a large distance is a fascinating phenomenon in itself. However, it could also serve as a resource for the teleportation of quantum information. One day, this might not only make it possible to communicate quantum information over very large distances, but might enable an entire quantum Internet."

The network is currently only at a prototype stage, but if it can be developed and scaled up, it could become the next generation in communication to relay not only quantum information -- but potentially form the basis of what Ritter calls 'an entire quantum Internet'.

The research is featured in the April 12 issue of Nature.

Image credit: Flickr

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