Wednesday, 16 May 2012

Exploiting Quantum Weirdness

After last week's news that physicists in Shanghai have smashed the distance record for teleporting photons, more research emerged this week about science striving to exploit quantum weirdness for
technological purposes.

Guan Ru Feng, again in China, but this time at Tsinghua University in Beijing has become the first scientist to create a simulation of quantum tunnelling, on a quantum computer.

Quantum tunnelling is the quantum-mechanical effect of transitioning through a classically-forbidden energy state. It plays an important role in phenomena such as nuclear fusion in stars. Tunnelling was predicted by Friedrich Hund and others as early as 1927, and has been accepted as a physical phenomenon for over 50 years.

An abstract of Guan Ru Feng's new paper, "Experimental Digital Simulation of Quantum Tunneling in a NMR Quantum Simulator", was published on arXiv on 11 May. The pithy abstract reads:
"It is well-known that quantum computers are superior to classical computers in efficiently simulating quantum systems. Here we report the first experimental simulation of the quantum tunneling through potential barriers, a widespread phenomenon of unique quantum feature [...] The occurrence of quantum tunneling through a barrier is clearly observed through the experimental result. This experiment has clearly demonstrated the viability of quantum simulation [...]"

So why is this significant? Well, quantum computers, as you may expect, are excellent at simulating quantum systems. As MIT's Technology Review explains, they've been used to simulate phenomenon such as quantum phase transitions and the dynamics of entanglement "things that classical computers simply cannot handle." But there is one quantum phenomenon that has never been simulated - tunnelling. This is the ability of quantum particles to cross a barrier without seeming to have passed through it.

The reason for this is the massive complexity of the task. As Technology Review remarks, it requires "numerous quantum logic gates processing dozens of qubits. That's always been beyond the state-of-the-art for quantum computing."

So the fact that Guan Ru Feng's team have now successfully simulated tunnelling suggests a significant advance in quantum computing, which will, no doubt, herald further simulations of much more complex phenomenon than we've seen to date.

Science is continuously and assiduously working towards harnessing quantum weirdness for practical technological applications. And it's interesting that so many of the recent advances in this field are coming from research Universities in China. Watch this space.


Tuesday, 15 May 2012

Tesla: the greatest geek who ever lived

The Oatmeal comic has published a lovely homage to science's
favourite forgotten genius, Nikola Tesla:

"On behalf of those who obsess, tinker & fix things that aren't
broken, thank you Nikola Tesla"


Monday, 14 May 2012

Physicists break distance record for teleportation


A few days ago a new paper published in arXiv indicated an exciting new development within the emerging science of teleportation.

In an advance that has significance for quantum computing and secure wireless communication, physicists at the University of Science and Technology in Shanghai have broken the record for the distance photons have been artificially teleported.  Their research is important, because teleportation is considered to be extremely useful for the future of secure communication across satellite networks.

MIT's Technology Review reports:

"Teleportation is the enabling technology behind quantum cryptography, a way of sending information with close-to-perfect secrecy. Because teleported information does not travel through the intervening space, it cannot be secretly accessed by an eavesdropper."
"Unfortunately, entangled photons are fragile objects. They cannot travel further than a kilometre or so down optical fibres because the photons end up interacting with the glass breaking the entanglement. That severely limits quantum cryptography's usefulness. However, physicists have had more success teleporting photons through the atmosphere."

Scientists at the University of Science and Technology in Shanghai have had considerable success with this technique. In 2010 they teleported photons 16km, and last week, they confirmed they have broken their own distance record by teleporting photons across 97km. Juan Yin, and his colleagues in Shanghai used a 1.3-watt laser to beam photons across the 97 km, and retrieve them at the final location.
Teleportation has moved on considerably in recent years, and is no longer the preserve of science-fiction, but rather an important new technology within communications, computing and cryptography.  Quantum teleportation takes advantage of quantum entanglement for the purposes of moving an object from one place to another without it ever moving in the space between. As Technology Review put it, "the idea is not that the physical object is teleported but the information that describes it."

Juan Yin's team in Shanghai have advanced the science of teleportation by developing a superior aiming technique, which prevents the disintegration of entanglement over short distances.  This has enabled them to increase the distance they can teleport photons from merely a few kilometres, to close to 100 kilometres.  Further improvements will be required in order for the technique to be of widespread use in secure satellite communications, but the rapid advances Juan in's team have made, suggest this is merely a matter of time.

As Juan Yin commented:
"The successful quantum teleportation [...] in combination with our high-frequency and high-accuracy [aiming] technique show the feasibility of satellite-based ultra-long-distance quantum teleportation".