German scientists link two labs with ‘universal quantum network’

Communicating with entangled distant atoms


German researchers have demonstrated a technique that allows them to create entanglement between atoms in different places, using photons to put the atoms into an entangled state.

Quantum effects have already crept into the cryptography world, in which entangled pairs of photons are used for key exchange. However, in the new experiment, the researchers have gone a step further: they’ve combined two kinds of quantum systems to crate a more general purpose network.

The setup works like this: a single rubidium atom is trapped in a reflective optical cavity, at each node of the network, with nodes connected via an optical fibre. Each of those rubidium atoms can act as a qubit (ie, able to store a quantum state).

When the atom emits a photon, the qubit – that is the state of the atom emitting the photon – is encoded into the photon’s polarization, and the destination node then takes on the state of the qubit that emitted the photon.

This arrangement means that atoms can be used to store qubits, while the photons are use to transmit state. It solves a challenge in quantum communications, since while photons work very well to transmit quantum states, they’re very difficult to store.

Researcher Stephan Ritter of the Max Planck Institute of Quantum Optics explained to Scientific American that the combination of atomic and photonic qubits was proposed 15 years ago, but it’s difficult to achieve in practice because "if you want to use single atoms and single photons, as we do, they hardly interact".

That’s where the reflective cavity comes in: when the photon arrives at its destination, it can be reflected past the rubidium atom tens of thousands of times, improving the chance that the desired interaction will actually happen.

“The cavity enhances the coupling between the light field and the atom,” Ritter says.

Hence the experiment achieves the genuinely spooky: a read-write operation across two laboratories connected by around 60 meters of fibre, in which the receiving atom becomes entangled with the transmitter, even though there’s been no direct interaction between them.

That, Ritter says, could extend the application of the network even further: once two atoms are entangled, the quantum state of one depends on the quantum state of the other.

As noted at Photonics.com, it only takes a microsecond to achieve the entanglement, but the state lasts 100 microseconds. That means it would be possible to build a network of “quantum repeaters” that use quantum teleportation, rather than photons, to transmit information between different places.

“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”, Ritter said.

The work is published in Nature. ®


Other stories you might like

  • Ubuntu 21.10: Plan to do yourself an Indri? Here's what's inside... including a bit of GNOME schooling

    Plus: Rounded corners make GNOME 40 look like Windows 11

    Review Canonical has released Ubuntu 21.10, or "Impish Indri" as this one is known. This is the last major version before next year's long-term support release of Ubuntu 22.04, and serves as a good preview of some of the changes coming for those who stick with LTS releases.

    If you prefer to run the latest and greatest, 21.10 is a solid release with a new kernel, a major GNOME update, and some theming changes. As a short-term support release, Ubuntu 21.10 will be supported for nine months, which covers you until July 2022, by which point 22.04 will already be out.

    Continue reading
  • Heart FM's borkfast show – a fine way to start your day

    Jamie and Amanda have a new co-presenter to contend with

    There can be few things worse than Microsoft Windows elbowing itself into a presenting partnership, as seen in this digital signage for the Heart breakfast show.

    For those unfamiliar with the station, Heart is a UK national broadcaster with Global as its parent. It currently consists of a dozen or so regional stations with a number of shows broadcast nationally. Including a perky breakfast show featuring former Live and Kicking presenter Jamie Theakston and Britain's Got Talent judge, Amanda Holden.

    Continue reading
  • Think your phone is snooping on you? Hold my beer, says basic physics

    Information wants to be free, and it's making its escape

    Opinion Forget the Singularity. That modern myth where AI learns to improve itself in an exponential feedback loop towards evil godhood ain't gonna happen. Spacetime itself sets hard limits on how fast information can be gathered and processed, no matter how clever you are.

    What we should expect in its place is the robot panopticon, a relatively dumb system with near-divine powers of perception. That's something the same laws of physics that prevent the Godbot practically guarantee. The latest foreshadowing of mankind's fate? The Ethernet cable.

    By itself, last week's story of a researcher picking up and decoding the unintended wireless emissions of an Ethernet cable is mildly interesting. It was the most labby of lab-based demos, with every possible tweak applied to maximise the chances of it working. It's not even as if it's a new discovery. The effect and its security implications have been known since the Second World War, when Bell Labs demonstrated to the US Army that a wired teleprinter encoder called SIGTOT was vulnerable. It could be monitored at a distance and the unencrypted messages extracted by the radio pulses it gave off in operation.

    Continue reading

Biting the hand that feeds IT © 1998–2021