Dr Menno Veldhorst, a UNSW Research Fellow and the lead author of the Nature paper, was equally delighted. “We’ve shown that a two-qubit logic gate – the central building block of a quantum computer – can be made in silicon, which we thought was a big deal. It’s nice to see that this has been recognised by our peers, and attracted industry attention.
“Because we use largely the same device technology as existing computer chips, we believe what we have made will be much easier to make into a full-scale processor chip than for any of the leading designs, which mostly rely on exotic elements and technologies. This makes building a quantum computer much more feasible, since it is based on the same manufacturing technology as today’s computer industry,” he added.
Dzurak noted that the team had recently “patented a design for a full-scale quantum computer chip that would allow for millions of our qubits, all doing the types of calculations that we’ve just experimentally demonstrated”.
The advance represents the final physical component needed to realise the promise of super-powerful silicon quantum computers, which harness the science of the very small – the strange behaviour of subatomic particles – to solve computing challenges that are beyond the reach of even today’s fastest supercomputers.
In classical computers, data is rendered as binary bits, which are always in one of two states: 0 or 1. However, a quantum bit (or ‘qubit’) can exist in both of these states at once, a condition known as a superposition. A qubit operation exploits this quantum weirdness by allowing many computations to be performed in parallel (a two-qubit system performs the operation on 4 values, a three-qubit system on 8, and so on).
“If quantum computers are to become a reality, the ability to conduct one- and two-qubit calculations are essential,” said Dzurak, who jointly led the team that in 2012 who demonstrated the first ever silicon qubit, also reported in Nature.
Until now, it had not been possible to make two quantum bits ‘talk’ to each other – and thereby create a logic gate – using silicon. “The silicon chip in your smartphone or tablet already has around one billion transistors on it, with each transistor less than 100 billionths of a metre in size,” said Veldhorst.
“We’ve morphed those silicon transistors into quantum bits by ensuring that each has only one electron associated with it. We then store the binary code of 0 or 1 on the ‘spin’ of the electron, which is associated with the electron’s tiny magnetic field,” he added.
Building a full-scale quantum processor would have major applications in the finance, security and healthcare sectors, allowing the identification and development of new medicines by greatly accelerating the computer-aided design of pharmaceutical compounds (and minimising lengthy trial and error testing); the development of new, lighter and stronger materials spanning consumer electronics to aircraft; and faster searching of massive databases.
Other researchers involved in the ‘top 10’ Nature paper include Professor Kohei M. Itoh of Japan’s Keio University – who provided specialised silicon wafers for the project – along with UNSW’s School of Electrical Engineering and Telecommunications Dr Henry Yang and Professor Andrea Morello, who leads the quantum spin control research team at CQC2T.
In November, Morello’s team proved – with the highest score ever obtained – that a quantum version of computer code can be written, and manipulated, using two quantum bits in a silicon microchip. This removes lingering doubts that such operations can be made reliably enough to allow powerful quantum computers to become a reality.
Only a month earlier, a team led by Simmons and CQC2T’s deputy director, Professor Lloyd Hollenberg of the University of Melbourne designed a 3D silicon chip architecture based on single atom quantum bits, compatible with atomic-scale fabrication techniques – providing a blueprint to build a large-scale quantum computer.
The full Physics World list of Top Ten Breakthroughs of 2015 can be found here.