A team of theoretical physicists from TU Eindhoven, Utrecht University, the University of Chile, Cedenna, and FOM has suggested a way to simulate black holes on an electronic chip. The technology used to create these manmade black holes may also be useful for quantum technologies. The research results will be published in Physical Review Letters on 1 February 2017.
Black holes are astronomical objects so dense that nothing, not even light, can escape their huge gravitational pull once it passes the event horizon (a point of no return). The researchers have found out how to make such event horizons for spin waves – fluctuations that propagate in magnetic materials. They use the behavior of the spin waves when these are influenced by electric currents.
Magnetic materials have two poles – north and south. If disturbed, the poles move from one position in the material to another in a wavelike manner called spin waves. The electrons in the material drag these waves along when an electric current runs through it. When such a current is passed through a wire that is thin on one end and thick on the other, the electrons flow slower on the thick end, just like water flows slower through a wide hose. The electrons on the thin end of the wire flow faster, and can flow so fast that the spin waves that are dragged along with them are not able to flow in the opposite direction anymore. The point at which this happens on the wire is where the spin waves reach a point of no return, equivalent to a black hole’s event horizon.
Gravitation close to astronomical black holes is so strong that it causes an event horizon for all types of particles. Once they pass a black hole’s event horizon, not even photons can escape from a black hole. Stephen Hawking discovered in 1974 that black holes emit radiation and are not completely black. Subtle quantum mechanical effects cause pairs of particles and antiparticles to disappear and appear continuously. When this happens near a black hole’s horizon, only one of the particles in the pair is occasionally swallowed by the black hole. The other particle then escapes and radiates away. The so-called Hawking radiation is nearly impossible to observe in outer space, as it is so small. Simulating the black hole on an electronic chip however, makes it possible to study this effect by looking at Hawking radiation of spin waves in a much simpler way.
The pairs of particles that cause Hawking radiation are quantum mechanically entangled. This means that their properties are so closely intertwined that classical physics can’t be used to describe them. Entanglement is one of the crucial ingredients of quantum technologies used in for example quantum computers. The researchers are now investigating, among other things, how devices that use this entanglement can be manufactured, and how these can then serve as building blocks for applications based on the quantum entanglement of spin waves.