Feeds

Scientists ‘untangle’ quantum communications

Faster without entanglement

Top three mobile application threats

Entanglement is one of the foundations of quantum communications, since that’s the property that makes quantum communication schemes secure*. So why is a group of scientists from Japan and the UK proposing to work without entanglement?

A study in Nature Photonics (abstract) led by Bill Munro – a research scientist with NTT’s Basic Research Laboratories in Japan – proposes just that: an entanglement-free quantum communications system that can transmit 107 quantum states per second.

The reason, Monro explained to The Register, is this: although entanglement leads to security, that’s not the only possible application of quantum communications. A quantum channel can also be used to communicate between quantum devices inside a quantum computer – in which case, speed is rather more important than security.

He also notes that achieving acceptable speed over long distance is a key focus of quantum communications research. Relatively slow communications in the terabit age is acceptable if the quantum channel is only being used for key distribution (with the key then used to encrypt a conventional communications channel), but not if you want to replace the classical channel entirely.

“What we are trying to do is to avoid having to create entanglement between repeater nodes (as this is slow and requires classical messaging)”, he told The Register.

These slow speeds are especially problematic when communicating over a long distance, something that requires repeaters, since an entanglement would have to be created between each pair of nodes on the network.

“For long distance quantum communication the potential rates of communication have been quite low (kHz or lower - with the limitation being caused by the classical communication time between nodes). Hence our scheme may be able to increase the communication rates,” Monro explained.

Security could still be added over the top, between the sender and receiver instead of at each hop, but the “no-entanglement” end-to-end link would reach further and at much greater speed than quantum communication schemes that rely on entanglement.

Even though there’s no entanglement, Munro said it’s clear that the scheme is transmitting superpositions (rather than, in a conventional optical network, using the frequency of light to signify the bit that’s being sent).

Munro’s scheme encodes states onto “matter qubits” (for example, using electron spin) at the originating and destination nodes. This state is transferred at the transmitter to a photon qubit, which is transmitted down a fibre to a receiver that reverses the process.

If the matter qubits needed to be entangled, they would have to be retained until the receiver process was complete, so the two ends could “compare notes” to determine that the photon’s state was preserved in the channel. Instead, the Munro scheme proposes to use a quantum parity code to check the received state – something the paper claims allows the system to tolerate photon losses in the channel as high as 50 percent (hence extending the range of the system to 17 km between nodes).

The paper states that 48 nodes would provide an 800 km quantum link that has a 98 percent probability of successfully transmitting the quantum information. The intermediate nodes in the network could also act as routers. ®

*Bootnote: El Reg is aware that perfect "quantum communications" security is a highly qualified and controversial topic.

3 Big data security analytics techniques

More from The Register

next story
Red-faced LOHAN team 'fesses up in blown SPEARS fuse fiasco
Standing in the corner, big pointy 'D' hats
KILLER SPONGES menacing California coastline
Surfers are safe, crustaceans less so
Opportunity selfie: Martian winds have given the spunky ol' rover a spring cleaning
Power levels up 70 per cent as the rover keeps on truckin'
KILLER ROBOTS, DNA TAMPERING and PEEPING CYBORGS: the future looks bright!
Americans optimistic about technology despite being afraid of EVERYTHING
Discovery time for 200m WONDER MATERIALS shaved from 4 MILLENNIA... to 4 years
Alloy, Alloy: Boffins in speed-classification breakthrough
Elon Musk's LEAKY THRUSTER gas stalls Space Station supply run
Helium seeps from Falcon 9 first stage, delays new legs for NASA robonaut
Fancy joining Reg hack on quid-a-day challenge?
Recruiting now for charity starvation diet
prev story

Whitepapers

Securing web applications made simple and scalable
In this whitepaper learn how automated security testing can provide a simple and scalable way to protect your web applications.
3 Big data security analytics techniques
Applying these Big Data security analytics techniques can help you make your business safer by detecting attacks early, before significant damage is done.
The benefits of software based PBX
Why you should break free from your proprietary PBX and how to leverage your existing server hardware.
Top three mobile application threats
Learn about three of the top mobile application security threats facing businesses today and recommendations on how to mitigate the risk.
Combat fraud and increase customer satisfaction
Based on their experience using HP ArcSight Enterprise Security Manager for IT security operations, Finansbank moved to HP ArcSight ESM for fraud management.