Quantum Computing Takes a Giant Step Closer to Reality

070504_Quantum_mechanics A team of scientists based at the London Centre for Nanotechnology and the National High Magnetic Field Lab (NHMFL) in Florida has discovered a new and more efficient way to encode quantum information within silicon that could bring the reality of a new era of quantum computing much closer.

Quantum computers have the potential to solve problems that would take a classical computer longer than the age of the universe. Quantum computation is a qualitatively new way of harnessing nature.

Quantum computing sounds like science fiction -as satellites, moon shots, and the original microprocessor once were.  But the age of computing in not even at the end of the beginning. 

Traditional computing, with its ever more microscopic circuitry etched in silicon, will soon reach a final barrier: Moore's law, which dictates that the amount of computing power you can squeeze into the same space will double every 18 months, is on course to run smack into a silicon wall by 2015, due to  overheating, caused by electrical charges running through ever more tightly packed circuits.

To leapfrog the silicon wall, we have to figure out how to manipulate the brain-bending rules of the quantum realm – an Alice in Wonderland world of subatomic particles that can be in two places at once. 

Where a classical computer obeys the well understood laws of classical physics, a quantum computer is a device that harnesses physical phenomenon unique to quantum mechanics (especially quantum interference) to realize a fundamentally new mode of information processing.

Despite being compatible with the silicon chips all around us, the chemical element bismuth has been overlooked to date in favour of phosphorus atoms in the race to quantum technologies. This is because today’s microelectronics use phosphorous dissolved in silicon.

However, the researchers have now found that bismuth atoms outperform phosphorus atoms. Bismuth is the heaviest stable atom and has a correspondingly large nuclear ‘spin’. Its quantum spin is like a tiny compass needle that can exist in one of ten states corresponding to different tilts (see image below) instead of the two directions available to a phosphorus nucleus. This allows bismuth nuclei to store much more quantum information than phosphorous nuclei.

The research, which is described in the journal Nature Materials and in a forthcoming article in Physical Review Letters, reveals the potential of bismuth atoms for building a quantum computer.

The observations lead to the suggestion of a ‘dream team’ using both bismuth and phosphorus atoms in silicon. As they are different, they can be manipulated independently. Bismuth would store quantum information while phosphorus controls the information flow.

Lead author Dr Gavin Morley of the London Centre for Nanotechnology said: “The experimental hurdles we’ve overcome in our research include using bismuth in silicon for the preparation, control and storage of quantum information. In this case bigger is better because the larger nucleus of bismuth provides more room for storing quantum information.”

Casey Kazan via University College London


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