What would you call two people wrapped up in a phone call? Phonon entanglement. This facetious example is actually very analogous to what has been accomplished in a quantum experiment involving two macroscopic (observable to the naked eye) sized diamonds. In this experiment, molecular assemblies seemed to be strongly interrelated between the two diamonds despite being separated by a sizable space. This instantaneous interaction at a distance, in which the quantum state of two particles – or in this case 1016 atoms – appear to be linked together is referred to as entanglement.
Normally this requires extremely cold temperatures (a few degrees above absolute zero), or special containment systems to keep the particles from interacting with the environment. But diamonds have several characteristics that obviate the need for these extreme conditions. Because of the rigid framework of the crystal lattice (the periodic geometry of the carbon atoms) small regions within the diamond are sufficiently shielded from environmental perturbations that entangled states can occur even at room temperature.
Since the first confirmation of this extraordinary phenomenon, with the demonstration of Bell’s inequality, entanglement had only been observed in exceedingly small numbers of particles – with 16 entangled spin states being the record.. until now. By utilizing a characteristic of solid-state matter known as phonon vibrations, which is a coherent (or synchronized) vibration of large molecular assemblies very similar to the vibration that occurs in the transmission of sound, researchers at Oxford University were able to link quadrillions of atoms together in two crystals six inches apart.
By directing a photon from a microwave laser pulse into the diamonds, the researchers were able to create phononic oscillations – imagine throwing a bowling ball into a spring mattress, where the bowling ball strikes the springs they will oscillate up and down. When the photon is directed through a beam splitter device and into two separate channels, it is considered to be in a quantum superposition – it is believed to be in both channels simultaneously (see our article Quantum Weirdness Replaced By Classical Fluid Dynamics to see why this interpretation may not be entirely accurate). Since it is as if one photon is creating a phonon in two separate crystals, they vibrate identically, and thus it is said the phononic state is entangled across the two crystals.
In more recent experiments, a team of researchers have succeeded in maintaining this remarkable state for several seconds, which could open the door for the use of diamonds in quantum computing or transmission of entangled photons over large distances. However, the methodology does not presently have a particularly high success rate – requiring around a million tries for one successful entanglement of phonons. But the theoretical utility of these results are astounding, as they demonstrate “quantum” behavior on a macroscopic scale. Showing how quantum phenomenon may not be as mysterious as we think, and in fact, characteristics such as entanglement may be fundamental to the structure and mechanics of our very Universe.
By: William Brown