January 30, 2015

Particle entanglement could revolutionize super-computers and communication

Eric Hopton for redOrbit.com - Your Universe Online

Even Sauron would be impressed.

Engineers have created a new micro-ring that “entangles” individual particles of light. This could be an important first step in a whole host of new technologies.

Entanglement, the instantaneous connection between two particles no matter how far they are apart, is one of those weird concepts thrown up by quantum physics that leaves most of us wondering “Could that really be true?” Einstein referred to it as, “spooky action at a distance”. It’s one of the most intriguing phenomena in all of physics, but now it seems it’s producing actual, practical applications to benefit us all.

Loops in silicon wafers

If properly harnessed, entangled photons could revolutionize computing, communications, and cyber security. Though they can be created in the lab and by comparatively large-scale optoelectronic components, finding a practical source of entangled photons that can fit onto an ordinary computer chip has been problematic.

New research, published in The Optical Society's (OSA) journal Optica, describes how a team of scientists has developed, for the first time, a microscopic component that is small enough to fit onto a standard silicon chip that can generate a continuous supply of entangled photons.

The new design is based on an established silicon technology known as a micro-ring resonator. These resonators are actually loops that are etched onto silicon wafers that can corral and then re-emit particles of light. By tailoring the design of this resonator, the researchers created a novel source of entangled photons that is incredibly small and highly efficient, making it an ideal on-chip component.

“The main advantage of our new source is that it is at the same time small, bright, and silicon based,” said Daniele Bajoni, a researcher at the Università degli Studi di Pavia in Italy and co-author on the paper. “The diameter of the ring resonator is a mere 20 microns, which is about one-tenth of the width of a human hair. Previous sources were hundreds of times larger than the one we developed.”

Two important implications

For many years, scientists and engineers have seen an enormous practical potential for entangled photons. This curious manifestation of quantum physics has two important implications in real-world technology.

First, if something acts on one of the entangled photons, the other 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 behavior could be harnessed to increase the power and speed of computations.

The second implication is that the two photons can be considered, in some sense, a single entity, which would allow for new communication protocols that are immune to spying.

This seemingly impossible behavior is essential, therefore, for the development of certain next-generation technologies, such as computers that are vastly more powerful than even today's most advanced supercomputers, and secure telecommunications.

Not so fast, though

To make these new technologies work, however, requires a new class of entangled photon emitters which can be readily incorporated into existing silicon chip technologies.

Until now, entangled photon emitters could be scaled down to only a few millimeters in size, which is still far too large for on-chip applications. These emitters also need a lot of power. To overcome these problems, the researchers looked at the potential of ring resonators as a new source for entangled photons. Ring resonators can be easily etched onto a silicon wafer in the same way that other components on semiconductor chips are formed. To power the resonator, a laser beam is directed along an optical fiber 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.

The researchers observed that, when photons exited the resonator, 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 Bajoni. “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.”

“In the last few years, silicon integrated devices have been developed to filter and route light, mainly for telecommunication applications,” said Bajoni. “Our micro-ring resonators can be readily used alongside these devices, moving us toward the ability to fully harness entanglement on a chip.” This research could pave the way for practical use of quantum information technologies, particularly quantum cryptography protocols, which would ensure secure communications in ways that classical cryptography protocols cannot.

According to Bajoni and his colleagues, these protocols have already been demonstrated and tested. Their work has shown how a cheap, small, and reliable source of entangled photons capable of propagation in fiber networks can be produced. As a result, practical applications for entanglement – that “spooky action at a distance” –  may become a reality.


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