COMPUTER ENGINEERS down under have claimed a breakthrough in quantum computing through coding which suggests that silicon can be used as the foundation for a powerful quantum computer.
The breakthrough was made by researchers at Australia's University of New South Wales (UNSW), who found that a quantum version of computer code can be written and manipulated using two quantum bits in a silicon microchip.
Using this theory, the scientists created an experiment based on a phenomenon known as quantum entanglement. This allows the measurement of one particle immediately affecting another, regardless of distance, even if they are at opposite ends of the universe.
The experiments leading up to the discovery, published in the international journal Nature Nanotechnology on Tuesday, were performed by project leader Andrea Morello and lead authors Stephanie Simmons and Juan Pablo Dehollain in a UNSW laboratory.
"The effect [of quantum entanglement] is famous for puzzling some of the deepest thinkers in the field, including Albert Einstein who called it ‘spooky action at a distance'," said Morello.
"Einstein was sceptical about entanglement, because it appears to contradict the principles of ‘locality', which means that objects cannot be instantly influenced from a distance."
Morello explained that because of this physicists have struggled for the past 50 years to establish a clear boundary between our everyday world and the quantum world, and that the best guide to that boundary has been a theorem called Bell's Inequality, which states that no local description of the world can reproduce all of the predictions of quantum mechanics.
Bell's Inequality demands a very stringent test to verify whether two particles are actually entangled, known as the ‘Bell test'.
"The key aspect of the Bell test is that it is extremely unforgiving: any imperfection in the preparation, manipulation and read-out protocol will cause the particles to fail the test," explained Dehollain.
"Nevertheless, we have succeeded in passing the test, and we have done so with the highest ‘score' ever recorded in an experiment."
The experiment placed two quantum particles - an electron and the nucleus of a single phosphorus atom - inside a silicon microchip. On top of each other, these particles have electron orbits around the nucleus. Therefore, there is no complication arising from the "spookiness" of action at a distance.
However, the experiment that created these two-particle entangled states is tantamount to writing a type of computer code that does not exist in everyday computers. The team therefore claim to have demonstrated the ability to write a purely quantum version of computer code, using two quantum bits in a silicon microchip to achieve the highest scores.
The researchers see this as a "key plank in the quest for super-powerful quantum computers of the future".
"Passing the Bell test with such a high score is the strongest possible proof that we have the operation of a quantum computer entirely under control," said Morello. "In particular, we can access the purely-quantum type of code that requires the use of the delicate quantum entanglement between two particles."
To put this in perspective, an every day computer can write four possible code words: 00, 01, 10 and 11. A quantum computer could write and use ‘superpositions' of the classical code words instead, such as (01 + 10), or (00 + 11), which requires the creation of quantum entanglement between two particles.
"These codes are perfectly legitimate in a quantum computer, but don't exist in a classical one," said Simmons. "This is, in some sense, the reason why quantum computers can be so much more powerful: with the same number of bits, they allow us to write a computer code that contains many more words, and we can use those extra words to run a different algorithm that reaches the result in a smaller number of steps."
Morello highlighted the importance of achieving the breakthrough using a silicon chip. "What I find mesmerising about this experiment is that this seemingly innocuous ‘quantum computer code' - (01 + 10) and (00 + 11) - has puzzled, confused and infuriated generations of physicists over the past 80 years," he said.
"Now, we have shown beyond any doubt that we can write this code inside a device that resembles the silicon microchips you have on your laptop or your mobile phone. It's a real triumph of electrical engineering." µ
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