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NIST's quantum boffins have TELEPORTED stuff over a HUNDRED KILOMETRES

No news on people beaming around via excitable Scots

By Alexander J Martin, 23 Sep 2015

Boffins at the US National Institute of Standards and Technology (NIST), collaborating with Japan's Nippon Telegraph and Telephone Corporation (NTT), have quadrupled the farthest distance quantum information has been "teleported".

Quantum teleportation, of course, is not a matter of making physical matter dematerialise and rematerialise in a different location of space, as per the USS Enterprise's transporter, but transporting information through some nifty – and difficult to comprehend – properties of the universe.

The record was described in a paper entitled Quantum teleportation over 100km of fibre using highly efficient superconducting nanowire single-photon detectors, and was published published in Optica.

Teleportation technology is considered to have applications in both quantum communications and quantum computing, which may allow light-speed processing, codebreaking and literally (as opposed to reasonably) unbreakable encryption.

Some, including the University of Cambridge's Ross Anderson, consider modern cryptographic practices sufficient and regard quantum crypto as an unproven, and possibly unprovable, physicists' quandry.

Credit: K Irvine/NIST

The abstract to the NIST paper explains: "Quantum teleportation is an essential quantum operation by which we can transfer an unknown quantum state to a remote location with the help of quantum entanglement and classical communication."

Since the first experimental demonstrations using photonic qubits and continuous variables, the distance of photonic quantum teleportation over free-space channels has continued to increase and has reached >100km.

On the other hand, quantum teleportation over optical fibre has been challenging, mainly because the multifold photon detection that inevitably accompanies quantum teleportation experiments has been very inefficient due to the relatively low detection efficiencies of typical telecom-band single-photon detectors.

The paper reports on meeting the challenges of quantum teleportation over optical fibre, specifically through the use of four "high-detection-efficiency superconducting nanowire single-photon detectors (SNSPDs)", which were developed by NIST.

These SNSPDs make it possible to perform highly efficient multifold photon measurements, allowing us to confirm that the quantum states of input photons were successfully teleported over 100km of fibre with an average fidelity of 83.7±2.0 per cent.

"Only about one per cent of photons make it all the way through 100km of fibre," noted NIST's Marty Stevens in a release. "We never could have done this experiment without these new detectors, which can measure this incredibly weak signal."

The lead author of the paper was Hiroki Takesue, a guest researcher at NIST, visiting from NTT, whose Basic Research Laboratories collaborated with the American institute for the research.

The heavy losses experienced in quantum data transmission has hitherto suppressed the rate and distance of that transmission.

However, the technique described in the paper and developed between NTT and NIST may allow for the creation of quantum communications repeaters, devices which handle signal degradation in classical communications networks by receiving a weak signal and rebroadcasting it at full strength.

NIST's boffins suggest this could extend quantum-network reach to such a degree that continued innovation in this area may eventually grace the Earth with a "quantum internet".

The detectors, which rely on "superconducting nanowires made of molybdenum silicide", are a recent advance in detector design from NIST, which feature the superconducting nanowires made from a new tungsten-silicon alloy.

The nanowires are so sensitive that they allow for the detection of individual packets of light and NIST has stated the detectors are capable of recording more than 80 per cent of arriving photons, revealing whether those photons are in the same or different time slots – the quantum state chosen for the experiment – each of which are just one nanosecond (10−9 seconds) long.

The NTT/NIST experiment filtered out and focused on such a limited combination of quantum states that teleportation could only be successful in 25 per cent of the transmissions. However, the efficient detectors allowed the boffins to successfully teleport the desired quantum state in, on average, 83 per cent of that maximum – meaning over 20 per cent of the total teleportations were successful.

The boffins stated that all of the experimental runs with different starting properties exceeded the 66.7 per cent success threshold, which is mathematically significant for proving the quantum nature of the teleportation process. ®

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