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Australian researchers amplify quantum information using teleportation

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November 27, 2012

Amplifying information – the key to the quantum Internet?

Amplifying information – the key to the quantum Internet?

The establishment of a worldwide quantum Internet would provide individuals, businesses, organizations, and governments access to intrinsically secure communications. However, absorption of photons in transit between internet nodes can dramatically reduce the efficiency of operating a quantum Internet. Now a research group at Australia's (CQCCT) has invented a way to recover some of the lost quantum information by teleporting the original information to another photon.

Quantum communication depends on maintaining the fidelity of the quantum information encoded on, e.g, a photon. If the fidelity is reduced, the efficiency of communication can be dramatically lowered. For example, in the likely case that a photon carrying a quantum bit (qubit) might be absorbed in transit, the resulting "noisy photon" is an entangled version of the photon with the quantum state of the vacuum, which contains no photons whatsoever. (Note that all the transmitter photons become noisy photons simply by travelling through conditions in which they might be absorbed.) Some of the information carried by the original photon is lost in the noisy photon, which can dramatically lower the efficiency of quantum communication applications.

The Center for Quantum Computation and Communication Technology (CQCCT) team has now invented a workaround for such information loss, which they call heralded state amplification. A herald is a classical signal that alerts one to an upcoming event. Imagine that, as a polite neighbor, you don't like to keep visitors waiting at the door. One approach is to stand at the door in case a visitor arrives, but this takes a lot of effort and prevents you from working on other tasks. It is more efficient to ignore the door until you hear the doorbell. The doorbell is a herald of arriving visitors.

The basic idea of heralded state amplification is that even though quantum information has been lost in a noisy photon, it is possible to improve the situation. Noisy photons pass through an analyzer that teleports the information to a second photon, and generates a herald when the second photon is less noisy than the original noisy photon.

The analyzer combines a noisy photon with a pure photon, producing three quantum states. Two of these are measured by photon detectors, while the third is the output of the analyzer. These three states are constructed so that when zero or two photons are detected, the output of the analyzer is noisier than is the input, while when exactly one photon is detected, the output is less noisy – the information has been amplified on the heralded output states.

To ensure that only amplified outputs are used for continued processing, a classical herald is generated by sending the detector outputs through an exclusive-or gate, so that a herald is generated when only one photon is detected by the detectors. The heralded state amplifier typically produces an information gain of five or less, but this is sufficient to rescue a large number of marginal communications applications. CQCCT's new heralded state amplifier thus represents an important addition to the quantum communications toolbox.

Source: Nature Physics

About the Author
Brian Dodson From an early age Brian wanted to become a scientist. He did, earning a Ph.D. in physics and embarking on an R&D career which has recently broken the 40th anniversary. What he didn't expect was that along the way he would become a patent agent, a rocket scientist, a gourmet cook, a biotech entrepreneur, an opera tenor and a science writer.   All articles by Brian Dodson
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9 Comments

Wait...this is all cool and clever but isn't there an elephant in the quantum room here?

How is the qubit "teleported"?

Is the writer misusing the term? "...an analyzer that teleports the information to a second photon..." should perhaps be "transcribes the information to a second photon..." or "transfers...."?

Am I missing something or do I have a misconception of the definition of "teleport"?

I'm fascinated so clarification (and my edification) would be appreciated.

Joseph Boe
28th November, 2012 @ 07:14 am PST

my brain just exploded

inchiki
28th November, 2012 @ 04:05 pm PST

inchiki, mine imploded, we both agree with Joesph

Bill Bennett
28th November, 2012 @ 09:04 pm PST

"Teleported" gives me problems, as what that entails, or how to do it is never explained. That verb may as well be "enchanted" or "bewitched" and no meaning would be lost.

sleat
29th November, 2012 @ 04:01 am PST

Oh I believe strongly in the future of communications via entangled photons, but in this case I fear that both photons, the carrier and the Herald could get absorbed and disappear

jochair
29th November, 2012 @ 04:03 am PST

Dang, can't even get more info from a check of the original source, as it's paywalled!

sleat
29th November, 2012 @ 04:08 am PST

Me too, HELP !!!

Alan Reid
29th November, 2012 @ 04:33 am PST

"teleported" in the context of this article has a different meaning than classical teleportation. Look up Quantum Teleportation on wikipedia: http://en.wikipedia.org/wiki/Quantum_teleportation

Kevin Brewster
29th November, 2012 @ 01:25 pm PST

Thank you Kevin. Several of the preceding seem to have become entangled with the issue.

Omen
4th December, 2012 @ 06:50 am PST
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