German scientists link two labs with ‘universal quantum network’ • The Register
andre.kesteloot at verizon.net
Thu Apr 12 11:10:43 CDT 2012
-------- Original Message --------
Subject: German scientists link two labs with ‘universal quantum
network’ • The Register
Date: Wed, 11 Apr 2012 23:02:55 -0400
From: André Kesteloot <andre.kesteloot at verizon.net>
To: Kesteloot André <andre.kesteloot at ieee.org>
> German scientists link two labs with ‘universal quantum network’
> Communicating with entangled distant atoms
> By Richard Chirgwin
> • Get more from this author
> Posted in Science <http://www.theregister.co.uk/science/>, 11th April
> 2012 23:48 GMT <http://www.theregister.co.uk/2012/04/11/> 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 <http://www.photonics.com/Article.aspx?AID=50601> 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 <http://dx.doi.org/10.1038/nature11023> in
> /Nature./ ®
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