Quantum Entanglement Now On-a-Chip

PORTLAND, Ore. -- Quantum computing promises to revolutionize future computers, enabling pint-sized hardware to outperform room-filing supercomputers, plus offers uncrackable encryption that foils all hackers no matter how skillful they are. The missing piece of the quantum puzzle was called "spooky action at a distance" by Einstein, namely a reliable source of entangled photons who mirror each others' state no matter how far apart on standard CMOS silicon chips.

Now Italian scientists at the Universit degli Studi di Pavia, in cooperation with the University of Glasgow and the University of Toronto, claim to have surmounted this last engineering hurdle.

"The idea is that pumping laser light inside a tiny ring enhances the probability of two photons interacting. We therefore decided that this enhancement could be used, in particular, for the production of entangled photon pairs," professor Daniele Bajoni at the Universit degli Studi di Pavia told EE Times. "In previous works, we discovered that confining light inside a ring resonator greatly enhances the interaction between light and matter, but our new results were realized by design, not by chance."

The most immediate application of quantum entanglement on a chip is uncrackable encryption, since all the chip maker has to do is build the silicon photon ring oscillator and use a popular quantum cryptography algorithm for entanglement which have already been proven in the lab (using bulky expensive equipment instead of a cheap silicon chip).

"The most typical algorithm for quantum cryptography using entanglement is the so-called Eckert protocol. In essence two parties (generally named Alice and Bob) exchange a set of entangled photon pairs, let us say idler photons are sent to Alice and signal photons are sent to Bob. Alice performs certain measurements on her photons, obtaining random results (let us say 1100101). If Bob performs the correct measurements on his photons, because of the entanglement, he will get the same string of random bits as Alice. The two can then use this string of random bits to encrypt signals to be sent on normal channels," Bajoni told us. "If someone eavesdrops the exchange of entangled photons between Alice and Bob, this action will change the properties of the photons, so that Alice and Bob can know if there is an eavesdropper: this makes the communication intrinsically secure."

For the future, the research group plans to add the other silicon photonics parts, using known means, to make a complete on-chip entanglement engine that can be used by others to realize specific encryption applications that have been dreamt of for decades, but which may now be realizable due to the new entangled photon source these researchers have invented.

"The obvious next steps will be to further integrate components on the chip. In our result we use the silicon ring resonator as a source of entangled photon, but then the filtering of the emitted light and the measurement of the entanglement is done via an external experimental set-up. All this external set-up can, ultimately, be integrated on a silicon chip too," Eckert told us. "And in related work, done with different authors in different collaborations, we have shown how to integrate spectral filters alongside the ring resonator. In the future we want to build the necessary interferometers and, if possible, the detectors, in a fully integrated platform. The final goal will be to have two chips, linked by fiber optics, performing key exchange for a complete quantum cryptography solution.

R. Colin Johnson, Advanced Technology Editor, EE Times

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Quantum Entanglement Now On-a-Chip