Tag Archives: quantum memories

Using sound to transfer quantum information

It seems sound is becoming more prominent as a means of science data communication (data sonification) and in this upcoming case, data transfer. From a June 5, 2018 news item on ScienceDaily,

Quantum physics is on the brink of a technological breakthrough: new types of sensors, secure data transmission methods and maybe even computers could be made possible thanks to quantum technologies. However, the main obstacle here is finding the right way to couple and precisely control a sufficient number of quantum systems (for example, individual atoms).

A team of researchers from TU Wien and Harvard University has found a new way to transfer the necessary quantum information. They propose using tiny mechanical vibrations. The atoms are coupled with each other by ‘phonons’ — the smallest quantum mechanical units of vibrations or sound waves.

A June 5, 2018 Technical University of Vienna (TU Wien) press release, which originated the news item, explains the work in greater detail,

“We are testing tiny diamonds with built-in silicon atoms – these quantum systems are particularly promising,” says Professor Peter Rabl from TU Wien. “Normally, diamonds are made exclusively of carbon, but adding silicon atoms in certain places creates defects in the crystal lattice where quantum information can be stored.” These microscopic flaws in the crystal lattice can be used like a tiny switch that can be switched between a state of higher energy and a state of lower energy using microwaves.

Together with a team from Harvard University, Peter Rabl’s research group has developed a new idea to achieve the targeted coupling of these quantum memories within the diamond. One by one they can be built into a tiny diamond rod measuring only a few micrometres in length, like individual pearls on a necklace. Just like a tuning fork, this rod can then be made to vibrate – however, these vibrations are so small that they can only be described using quantum theory. It is through these vibrations that the silicon atoms can form a quantum-mechanical link to each other.

“Light is made from photons, the quantum of light. In the same way, mechanical vibrations or sound waves can also be described in a quantum-mechanical manner. They are comprised of phonons – the smallest possible units of mechanical vibration,” explains Peter Rabl. As the research team has now been able to show using simulation calculations, any number of these quantum memories can be linked together in the diamond rod thanks to these phonons. The individual silicon atoms are “switched on and off” using microwaves. During this process, they emit or absorb phonons. This creates a quantum entanglement of different silicon defects, thus allowing quantum information to be transferred.

The road to a scalable quantum network
Until now it was not clear whether something like this was even possible: “Usually you would expect the phonons to be absorbed somewhere, or to come into contact with the environment and thus lose their quantum mechanical properties,” says Peter Rabl. “Phonons are the enemy of quantum information, so to speak. But with our calculations, we were able to show that, when controlled appropriately using microwaves, the phonons are in fact useable for technical applications.”

The main advantage of this new technology lies in its scalability: “There are many ideas for quantum systems that, in principle, can be used for technological applications. The biggest problem is that it is very difficult to connect enough of them to be able to carry out complicated computing operations,” says Peter Rabl. The new strategy of using phonons for this purpose could pave the way to a scalable quantum technology.

Here’s a link to and a citation for the paper,

Phonon Networks with Silicon-Vacancy Centers in Diamond Waveguides by M.-A. Lemonde, S. Meesala, A. Sipahigil, M. J. A. Schuetz, M. D. Lukin, M. Loncar, and P. Rabl. Phys. Rev. Lett. 120 (21), 213603 DOI:https://doi.org/10.1103/PhysRevLett.120.213603 Published 25 May 2018

This paper is behind a paywall.

Quantum teleportation

It’s been two years (my Aug. 16, 2013 posting features a German-Japanese collaboration) since the last quantum teleportation posting here. First, a little visual stimulation,

Captain James T Kirk (credit: http://www.comicvine.com/james-t-kirk/4005-20078/)

Captain James T Kirk (credit: http://www.comicvine.com/james-t-kirk/4005-20078/)

Captain Kirk, also known as William Shatner, is from Montréal, Canada and that’s not the only Canadian connection to this story which is really about some research at York University (UK). From an Oct. 1, 2015 news item on Nanotechnology Now,

Mention the word ‘teleportation’ and for many people it conjures up “Beam me up, Scottie” images of Captain James T Kirk.

But in the last two decades quantum teleportation – transferring the quantum structure of an object from one place to another without physical transmission — has moved from the realms of Star Trek fantasy to tangible reality.

A Sept. 30, 2015 York University (UK) press release, which originated the news item, describes the quantum teleportation research problem and solution,

Quantum teleportation is an important building block for quantum computing, quantum communication and quantum network and, eventually, a quantum Internet. While theoretical proposals for a quantum Internet already exist, the problem for scientists is that there is still debate over which of various technologies provides the most efficient and reliable teleportation system. This is the dilemma which an international team of researchers, led by Dr Stefano Pirandola of the Department of Computer Science at the University of York, set out to resolve.

In a paper published in Nature Photonics, the team, which included scientists from the Freie Universität Berlin and the Universities of Tokyo and Toronto [emphasis mine], reviewed the theoretical ideas around quantum teleportation focusing on the main experimental approaches and their attendant advantages and disadvantages.

None of the technologies alone provide a perfect solution, so the scientists concluded that a hybridisation of the various protocols and underlying structures would offer the most fruitful approach.

For instance, systems using photonic qubits work over distances up to 143 kilometres, but they are probabilistic in that only 50 per cent of the information can be transported. To resolve this, such photon systems may be used in conjunction with continuous variable systems, which are 100 per cent effective but currently limited to short distances.

Most importantly, teleportation-based optical communication needs an interface with suitable matter-based quantum memories where quantum information can be stored and further processed.

Dr Pirandola, who is also a member of the York Centre for Quantum Technologies, said: “We don’t have an ideal or universal technology for quantum teleportation. The field has developed a lot but we seem to need to rely on a hybrid approach to get the best from each available technology.

“The use of quantum teleportation as a building block for a quantum network depends on its integration with quantum memories. The development of good quantum memories would allow us to build quantum repeaters, therefore extending the range of teleportation. They would also give us the ability to store and process the transmitted quantum information at local quantum computers.

“This could ultimately form the backbone of a quantum Internet. The revised hybrid architecture will likely rely on teleportation-based long-distance quantum optical communication, interfaced with solid state devices for quantum information processing.”

Here’s a link to and a citation for the paper,

Advances in quantum teleportation by S. Pirandola, J. Eisert, C. Weedbrook, A. Furusawa, & S. L. Braunstein. Nature Photonics 9, 641–652 (2015) doi:10.1038/nphoton.2015.154 Published online 29 September 2015

This paper is behind a paywall.