Australian researchers have proven that it is possible to write a reliable computer code using quantum technology in a silicon microchip, paving the way for future practical quantum computers.
The team from the University of New South Wales placed two quantum particles – an electron and the nucleus of a single phosphorus atom – inside a microchip to create not only the standard bits of information 00, 01, 10 and 11 as known from conventional computing, but also so called superpositions that take advantage of quantum entanglement.
"These codes are perfectly legitimate in a quantum computer, but don't exist in a classical one," said UNSW Research Fellow Stephanie Simmons, a co-author of the experiment described in the latest issue of Nature Nanotechnology. "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."
The two particles in the microchip are placed on top of each other, which makes proving their entanglement considerably easier than if they were located further apart.
In fact, quantum entanglement expects the two particles to be able to affect each other even if at opposite ends of the universe.
To prove that the two particles are reliably entangled and therefore that the code is reliable, the experiment had to pass the so called Bell test, devised by British physicist John Bell in the 1960s.
"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," said Juan Pablo Dehollain, the lead author of the paper.
"Nevertheless, we have succeeded in passing the test, and we have done so with the highest 'score' ever recorded in an experiment.”
Passing the Bell test means the researchers have the entanglement and thus the processes inside the quantum computer entirely under control.
“We can access the purely-quantum type of code that requires the use of the delicate quantum entanglement between two particles," said Professor Andrea Morello who led the research.
"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. 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 added.