Scientists Entangle Diamonds Using Vibrations

It seems that Einstein’s spooky action at a distance’ can manifest itself on a macroscopic scale and set two disparate diamonds into entangled’ vibrations. Physicists at University of Oxford, UK, have demonstrated that even diamonds can be quantum mechanically entangled, something that had troubled Einstein deeply as early as the 1930’s.

Diamonds vibrating in sync. Courtesy: Nature communications

What is Entanglement?

Entanglement between two states means that if you alter one state, then the other state automatically responds to it. A simplified version of the entanglement problem was put forward by Einstein, Podolosky and Rosen (EPR) in 1933 and goes like this. If we took two electrons in an orbit, their spin would necessarily be opposite. If one was spinning up, the other would be spinning down. Now, if you separate the two electrons, without ever observing them, by very large distances Einstein said, half the length of the known Universe then, if you observe one, you would automatically know about the spin state of the other. Say, you observe your electron to be in the spin-up state. Since the other electron has to be in the other spin state, it will be in the spin-down state. You’d know this instantly! In other words, you have just transferred information about an electron half the way into the Universe instantly! This is in blatant conflict with Special Relativity. The phenomenon is so detestable, that Einstein compared it with voo-doo, thus coining the phrase Spooky action at a distance’.

Several attempts have been made to make sense out of this. The most respectable argument is that information is not really being transferred. The EPR paradox has also been tested in the laboratory, using entangled photons. Every time quantum mechanics seems to triumph and physicists remain as puzzled as Einstein.

The Present Experiment

In this latest attempt the Oxford group, led by Ian Walmsley, entangled vibrations in a diamond crystal. They fired a laser pulse at two diamonds separated by 15 cm. Each of the pieces were 3 mm wide. The laser would induce vibrations inside the crystals, giving off particles called phonons’, which are quanta of vibrations. The team claims that the disturbance spans 1016 atoms, which makes the vibrating area visible even without a microscope.

Here’s the crucial point! You cannot know which crystal is vibrating, unless you observe them. Automatically, you know something about the other crystal.

The Experimental Work Done – Exciting vibrations

This is how the experimentalists went about their job. They fired a laser at a beam splitter. This, true to its name, split the beam into two. One photon cannot be split up and has to go to either one of the crystals. Once there, it excites a phonon (i.e. induces a vibration). Since, we did not know which crystal the photon had gotten into, the photon was entangled. Once it transfers part of its energy to the phonon, the crystal can emit a low energy photon. This is what is detected and this signals that a phonon has been created. Since, we do not know which crystal the phonon is created in, the crystals are entangled.

Detecting where it came from!

In order to know which crystal is vibrating, the team fired another laser beam at the crystals. This draws out the phonon energy and leaves the crystal as it was before the first laser was fired. The light emitted must have a frequency greater than the one sent in. Scientists arranged for two detectors, one for each crystal, to detect the photons. We would expect 50% chance for each of the the detectors to go off, but what is observed is that the two crystals behave as if they were one entity. Only one of the detectors go off at a time!! They are entangled.

The results were reported in a paper in Nature published today, i.e. on the 2nd of December.

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Debjyoti Bardhan

Is a science geek, currently pursuing some sort of a degree (called a PhD) in Physics at TIFR, Mumbai. An enthusiastic but useless amateur photographer, his most favourite activity is simply lazing around. He is interested in all things interesting and scientific.