Until now, it has been confined at the tiniest levels

Sep 29, 2009 10:58 GMT  ·  By
For the first time, Quantum entanglement was proven at the macroscale, between two superconductors located millimeters apart
   For the first time, Quantum entanglement was proven at the macroscale, between two superconductors located millimeters apart

Scientists at the University of California in Santa Barbara (UCSB) have recently managed to demonstrate that the quantum entanglement effect – one of the basic ones in quantum physics – can be observed at a large scale as well, and that it is not necessarily confined to the elementary-particle level. The team that detailed its finds in the September 24 issue of the journal Nature also shows that billions of electrons flowing in superconductor materials can collectively exhibit this property.

“It’s an exciting piece of work. People are interested in pushing the boundaries of quantum mechanics,” Yale University physicist Steven Girvin says of the work. Quantum entanglement is one of the more peculiar consequences of quantum mechanics, and is characterized by the fact that interacting particles become somehow linked to each other at some point, as in entangled. This means that whatever happens to one of them affects the others directly, even if they are not in contact with each other. Ions, photons and atoms have thus far been the only classes of particles in which quantum entanglement was scientifically observed.

The UCSB team, led by expert John Martinis, devised a simple experiment to prove the quantum principle. They placed two superconductor materials on a small chip. Each of the aluminum-based superconductors was less than one millimeter across, and they were placed a few millimeters apart from each other. The entire setup was then exposed to very low temperatures, which allowed for electrons to flow between the two devices without meeting any resistance. The experts noticed that all the electrons within the superconductors moved together, in a naturally coherent way, which was unexpected.

“There are very few moving parts, so to speak. It’s a general fact that the larger an object is, the more classical it is in its behavior, and the more difficult it is to see quantum mechanical effects,” Girvin says. In a follow-up experiment, Martinis and his team used microwave pulses to ensure that entanglement was truly at work. They hypothesized that, if the spin of electrons in one superconductor was clockwise, the other would be clockwise. In order to test the accuracy of their own calculations, team members measured the quantum state about 34 million times.

If classical physics had been at work, Martinis reveals, then the electron flows should have acted independently of each other. However, an extremely large percentage of the measurements revealed that the spins were opposite, thus demonstrating quantum entanglement at the large scale. “It has to be in this weird quantum state for you to get those particular probabilities that we measure. The percentages of those different things are not something that you can classically predict,” Martinis says.

“It’s interesting to test quantum mechanics on a large scale. Do things look classical on large scales because there’s something wrong with quantum mechanics? Personally, I think that’s wrong, but one never knows,” Girvin concludes, quoted by Wired.