Discordant bits and single photons boost quantum power

Exploiting the weirdness inherent in the quantum world to create new technologies just got a little easier, thanks to two breakthroughs. One suggests that an untapped quantum phenomenon previously dismissed as mere "noise" could give quantum computers a boost. The second harnesses objects known as quantum dots, used previously in brain science and computing, to make quantum code-sharing more secure.
The quantum world, with particles that can be in multiple places at once, is known for its strange properties. Perhaps the most famous example is entanglement, which inextricably links particles no matter how far apart they are in space.
Most quantum computers exploit entanglement: the idea is that some problems could be run much faster on a computer that has entangled quantum bits, or qubits, instead of ordinary ones. But entanglement has proved difficult to tame, especially outside the lab.
Now Mile Gu of the Centre for Quantum Technologies at National University of Singapore and colleagues have shown that a property called quantum discord might replace it in quantum computing.
Quantum discord is a type of interference and was previously dismissed as unhelpful noise. But when Gu's team used the phenomenon to encode information into laser light, they found that this increased the amount of original information that they could retrieve afterwards. Their experiment doesn't count as a quantum computation, but it hints at a new way of doing quantum computing that is free of pesky entanglement. Gu told PhysOrg:
"Our research has identified that quantum discord, a more robust and easy-to-access phenomenon than entanglement, can also deliver quantum advantage."
Computing isn't the only potential application of quantum weirdness. Sven Hoefling and colleagues at the University of Würzburg in Germany have found a way to increase the security of quantum key distribution, in which a secret key that can subsequently be used to encrypt a message is transmitted via single photons.
QKD is secure because once a quantum object, such as a single photon, has been observed, it is irrevocably changed. So if the key is intercepted by an eavesdropper, the receiver would know about it.
The trouble is that producing just one photon is not easy. Until now most QKD experiments have been performed by winnowing down streams of photons emitted by lasers. But there is always a chance that an extra photon has slipped through, in which case the key might be intercepted without the receiver's knowledge.
Hoefling and colleagues instead transmitted a key using photons produced by quantum dots, nanoparticles capable of producing single photons without the need for a filter.
Quantum dots, also touted for their potential to form computer memories, and more recently to activate brain cells, have the advantage of being made from semiconductors, which may make them easier to convert into a commercial technology. As Hoefling told the BBC:
"Semiconductors are at the heart of all the technology we use. You can really benefit from that, because you don't need to make a whole new chain of technology."