Tag Archives: N.K. Langford

Entangling diamonds

Usually when you hear about entanglement, they’re talking about quantum particles or kittens. On Dec. 2, 2011, Science magazine published a paper by scientists who had entangled diamonds (that can be touched and held in human hands). From the Dec. 1, 2011 CBC (Canadian Broadcasting Corporation) news article by Emily Chung,

Quantum physics is known for bizarre phenomena that are very different from the behaviour we are familiar with through our interaction with objects on the human scale, which follow the laws of classical physics. For example, quantum “entanglement” connects two objects so that no matter how far away they are from one another, each object is affected by what happens to the other.

Now, scientists from the U.K., Canada and Singapore have managed to demonstrate entanglement in ordinary diamonds under conditions found in any ordinary room or laboratory.

Philip Ball in his Dec. 1, 2011 article for Nature magazine describes precisely what entanglement means when applied to the diamond crystals that were entangled,

A pair of diamond crystals has been linked by quantum entanglement. This means that a vibration in the crystals could not be meaningfully assigned to one or other of them: both crystals were simultaneously vibrating and not vibrating.

Quantum entanglement — interdependence of quantum states between particles not in physical contact — has been well established between quantum particles such as atoms at ultra-cold temperatures. But like most quantum effects, it doesn’t tend to survive either at room temperature or in objects large enough to see with the naked eye.

Entanglement, until now, has been demonstrated at very small scales due to an issue with coherence and under extreme conditions. Entangled objects are coherent with each other but other objects such as atoms can cause the entangled objects to lose their coherence and their entangled state. In order to entangle the diamonds, the scientists had to find a way of dealing with the loss of coherence as the objects are scaled up and they were able to achieve this at room temperature. From the Emily Chung article,

Walmsley [Ian Walmsley, professor of experimental physics at the University of Oxford] said it’s easier to maintain coherence in smaller objects because they can be isolated practically from disturbances. Things are trickier in larger systems that contain lots of interacting, moving parts.

Two things helped the researchers get around this in their experiment, Sussman [Ben Sussman, a quantum physicist at the National Research Council of Canada and adjunct professor at the University of Ottawa] said:

  • The hardness of the diamonds meant it was more resistant to disturbances that could destroy the coherence.
  • The extreme speed of the experiment — the researchers used laser pulses just 60 femtoseconds long, about 6/100,000ths of a nanosecond (a nanosecond is a billionth of a second) — meant there was no time for disturbances to destroy the quantum effects.

Laser pulses were used to put the two diamonds into a state where they were entangled with one another through a shared vibration known as a phonon. By measuring particles of light called photons subsequently scattered from the diamonds, the researchers confirmed that the states of the two diamonds were linked with each other — evidence that they were entangled.

If you are interested in the team’s research and can get past Science magazine’s paywall, here’s the citation,

“Entangling Macroscopic Diamonds at Room Temperature,” by K.C. Lee; M.R. Sprague; J. Nunn; N.K. Langford; X.-M. Jin; T. Champion; P. Michelberger; K.F. Reim; D. England; D. Jaksch; I.A. Walmsley at University of Oxford in Oxford, UK; B.J. Sussman at National Research Council of Canada in Ottawa, ON, Canada; X.-M. Jin; D. Jaksch at National University of Singapore in Singapore. Science 2 December 2011: Vol. 334 no. 6060 pp. 1253-1256 DOI: 10.1126/science.1211914

All of the media reports I’ve seen to date focus on the UK and Canadian researchers and I cannot find anything about the contribution of the researcher based in Singapore.

I do wish I could read more languages as I’d be more likely to find information about work which is not necessarily going to be covered in English language media.