University of New South Wales (UNSW) researchers have written and manipulated a quantum version of computer code in a silicon microchip.
The result was published in the international journal, Nature Nanotechnology, today.
The quantum code written at UNSW is built upon a class of phenomena called quantum entanglement, which allows for the measurement of one particle affecting another- even if they are at opposite ends of the universe.
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. These particles are on top of each other – the electron orbits around the nucleus.
UNSW centre for Quantum Computation and Communication Technology program manager Professor Andrea Morello said that creating the 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 for super-powerful quantum computers of the future,” he said.
The research passed the Bell Inequality test which is designed to verify if two particles are actually entangled. It is named after British physicist John Bell who devised the theorem in 1964.
“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.”
He explained that in a normal computer, using two bits one could 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.
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.”
“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.
According to paper co-author and UNSW research fellow Stephanie Simmons, the codes are perfectly legitimate in a quantum computer but don’t exist in a classical computer.
“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 work was supported by Professor Andrew Dzurak and his team at UNSW, together with collaborators from the University of Melbourne and Japan’s Keio University.