​Researchers write quantum code in silicon

​Researchers write quantum code in silicon

UNSW scientists say operations like this are reliable enough to make quantum computers a reality

UNSW researchers Andrea Morello (left), with Dr Juan Pablo Dehollain and Dr Stephanie Simmons

UNSW researchers Andrea Morello (left), with Dr Juan Pablo Dehollain and Dr Stephanie Simmons

Australian engineers have proven that a quantum version of computer code can be written, and manipulated, using two quantum bits in a silicon microchip.

The result was obtained by quantum computing specialists at the University of New South Wales who said this latest advance removed lingering doubts that operations like this can be made reliably enough to allow powerful quantum computers to become a reality.

The quantum code written by UNSW researchers is built on the ‘quantum entanglement’ phenomena where sub-atomic particles become so entwined that they share the same properties even when they have been separated.

This allows for counterintuitive phenomena such as the measurement of one particle instantly affecting another – even if they are at opposite ends of the universe.

“This effect is famous for puzzling some of the deepest thinkers in the field, including Albert Einstein, who called it ‘spooky action at a distance,’” said professor Andrea Morello of the School of Electrical Engineering & Telecommunications at UNSW.

“Einstein was skeptical about entanglement because it appears to contradict the principles of ‘locality’, which means that objects cannot be instantly influenced from a distance,” Morello said.

UNSW said physicists have struggled to establish a clear boundary between the everyday world and the strange quantum world. For 50 years, the best guide to this boundary has been the ‘Bell’s Inequality’ theorem, which says that no local description of the world can reproduce all of the predictions of quantum mechanics.

Bell’s Inequality demands a stringent test to verify if two particles are entangled, known as the ‘Bell test.’

“A 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,” said Dr Juan Pablo Dehollain, a UNSW research associate.

“Nevertheless, we have succeeded in passing the test, and we have done so with the highest score ever recorded in an experiment,” Dehollain said.

Dehollain and Dr Stephanie Simmons were lead authors of this latest finding in the Nature Nanotechnology paper.

Passing the Bell test with such a high score is the strongest proof that researchers have the operation of a quantum computer under control, Dr Morello said.

“In particular, we can access the ‘purely quantum’ type of code that requires the use of the delicate quantum entanglement between two particles.”

In a normal computer using two bits, four possible code words can be written: 00, 01, 10, and 11. In a quantum computer, a programmer can 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.

“These codes are perfectly legitimate in a quantum computer, but don’t exist in a classical one,” said Dr Simmons.

Quantum computers are so powerful because they enable researchers to write computer code that contains many more ‘code words’ than a classical computer, Dr Simmons said.

“We can use those extra words to run a different algorithm that reaches the result in a smaller number of steps,” Dr Simmons said.

Morello said what he found mesmerising about this experiment is that the seemingly innocuous quantum computer code (01+10) and (00+11) has puzzled, confused and infuriated physicists over the past 80 years.

“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,” he said.

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