Evrim Yazgin
Cosmos science journalist
The year of quantum is playing host to a vast number of new quantum research papers and slowly they are filling the void of what is known, and what might prove useful to our future.
Physicists have for the first time seen entanglement of the “total angular momentum” of light particles in nanoscale structures. The discovery may have implications for next-generation quantum communication and computing components.
Quantum entanglement is an effect where entangled particles can communicate and share a single quantum state instantly no matter how far apart they are. It is an integral part of quantum communication through so-called “quantum teleportation” where quantum information can be transmitted instantly between devices.
Photons – particles of light – have been shown to exhibit quantum entanglement in a number of different ways. Physicists have entangled photons where they have shared direction of travel, colour and electric field direction.
But the new research, published in Nature, is the first time that photons’ total angular momentum is entangled.
Angular momentum is momentum related to rotation.
In quantum mechanics, angular momentum comes in different forms which can be imagined (though the physics is very different) like the movement of the Earth in space.
The two types of quantum angular momentum are spin – related to the rotation of the particle’s electric field (this can be thought of like the rotation of the Earth) – and orbital angular momentum – related to the particle’s rotation in space (this can be thought of like Earth’s orbit around the Sun).
When photons are crammed into structures smaller than the photon’s wavelength, these 2 properties appear as one: the total angular momentum (TAM).
Being able to put photons into smaller spaces is useful for miniaturising devices and for increasing the interaction between the photon and the material the photon is traveling in, allowing for different kinds of phenomena to be produced.
The new research shows that photons put into nanostructures a thousand times smaller than the width of a human hair become entangled in their TAM.
It is the first time a new type of quantum entanglement has been found in more than 20 years.
“We observe that entanglement in TAM leads to a completely different structure of quantum correlations of photon pairs, compared with entanglement related to the two constituent angular momenta,” the authors write. “This work paves the way for on-chip quantum information processing using the TAM of photons as the encoding property for quantum information.”
