Engineering researchers at UNSW have proven that a quantum version of computer code can be written and manipulated using two quantum bits in a silicon microchip.
Professor Andrea Morello from the UNSW School of Electrical Engineering & Telecommunications led the research and said the code uses quantum entanglement, a contentious area of quantum physics that has challenged some of the greatest thinkers in the field.
“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,” said Morello.
Irish physicist John Stewart Bell devised a stringent test to determine whether particles are entangled or not. The UNSW researchers claim to have passed his test with the highest ‘score’ ever recorded.
“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.”
In the UNSW experiment, the two quantum particles involved were an electron and the nucleus of a single phosphorus atom, placed inside a silicon microchip. Because the electron orbits around the nucleus, there is no complication arising from non-locality or what Einstein referred to as “spookiness of action at a distance”.
Morello said that creating these two-particle entangled states is tantamount to writing a type of computer code that does not exist in everyday computers. It therefore demonstrates the ability to write a purely quantum version of computer code, using two quantum bits in a silicon microchip – a key plank in the quest to build super-powerful quantum computers of the future.
In a normal computer, using two bits it is possible to write four possible code words: 00, 01, 10 and 11. In a quantum computer, instead, one can also write and use ‘superpositions’ of the classical code words, such as (01 + 10), or (00 + 11). This requires the creation of quantum entanglement between two particles.
“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.”
An illustration of coding in quantum entanglement, courtesy UNSW.