For the first time, engineers have managed to create a micro-ring that entangles individual particles of light. In the journal Optica published on 26 January, the team from the University of Pavia in Italy describe a microscopic component small enough to fit onto a standard silicon chip that can generate a continuous supply of entangled photons, which could lead to considerable advances in computing, communications, and cyber security.
Entanglement – the instantaneous connection between two particles no matter their distance apart – is one of the most promising phenomena in all of physics. Although it can be created in the lab and by large-scale optoelectronic components, a practical source of entangled photons that can fit onto an ordinary computer chip has been elusive.
The new design is based on a micro-ring resonator - loops that are etched onto silicon wafers that can corral and then reemit particles of light. By tailoring the design of this resonator, the researchers created a novel source of entangled photons that is extremely small - just 20µm, 100 times smaller than previous components - and highly efficient, making it an ideal on-chip component.
The researchers believe their work is particularly relevant because it demonstrates, for the first time, a quintessential quantum effect, entanglement, in a well-established technology.
Scientists and engineers have long recognised the enormous potential of entangled photons.
First, if something acts on one of the entangled photons then the other one will respond to that action instantly, even if it is on the opposite side of a computer chip or even the opposite side of the Galaxy. This behaviour could be harnessed to increase the power and speed of computations. The second implication is that the two photons can be considered to be, in some sense, a single entity, which would allow for new communication protocols that are immune to spying.
However, to enable the development of new technologies, entangled photon emitters that can be incorporated into existing silicon chip technologies had to be developed.
The researchers explored the potential of ring resonators as a new source for entangled photons. These well-established optoelectronic components can be easily etched onto a silicon wafer in the same manner that other components on semiconductor chips are fashioned. To pump the resonator, a laser beam is directed along an optical fibre to the input side of the sample, and then coupled to the resonator where the photons race around the ring. This creates an ideal environment for the photons to mingle and become entangled.
As photons exited the resonator, the researchers were able to observe that a remarkably high percentage of them exhibited the telltale characteristics of entanglement.
‘Our device is capable of emitting light with striking quantum mechanical properties never observed in an integrated source,’ said Daniele Bajoni, a researcher at the University of Pavia and co-author on the paper. ‘The rate at which the entangled photons are generated is unprecedented for a silicon integrated source, and comparable with that available from bulk crystals that must be pumped by very strong lasers.’