The quest for a silicon quantum computer


University: UNSW Sydney

Authors Centre Participants: Prof. Michelle Y. Simmons AO, Prof. Andrew S. Dzurak, Prof. Andrea Morello, Prof. Sven Rogge

Other Source: COSMOS Magazine

Three teams of Australian researchers are racing to make a silicon quantum computer.

Full article by Wilson da Silva published in COSMOS Magazine 13 September 2017

CQC²T’s UNSW quantum computing effort is focused on creating solid-state devices in silicon, the heart of the US$380 billion global semiconductor industry that makes all of the world’s computer chips. And they’re not just creating ornate designs to show off how many qubits can be packed together, but aiming to build qubits that could one day be easily fabricated – and scaled up to the thousands, millions and billions.

“The infrastructure you need to make the kind of silicon qubit devices we build is unheard of in a university environment,” says Prof Andrea Morello, CQC²T Program Manager. “There’s basically no one else in a university setting that has access to these sort of advanced facilities.”

Prof Andrew Dzurak, is the Director of the UNSW node of the Australian National Fabrication Facility, and Program Manager at CQC²T . UNSW’s 750m2 facility is an advanced nanoscale manufacturing hub with a complete silicon metal-oxide- semiconductor process line – the precise infrastructure needed to make silicon qubit devices.

“The complexity of the infrastructure necessary to fabricate at that scale and with that level of precision is only found in billion-dollar factories where silicon integrated circuits are made,” says Dzurak. “Our goal is to develop, and demonstrate, the science and engineering of building a 10-qubit silicon device within five years. Ideally, you want to get to 10 qubits using a method that doesn’t substantially deviate from the way that a billion transistors are put on a chip.”

Morello adds: “If you can do that, then you’ve hit the jackpot, because we would then know how to make a qubit chip at scale and sell it at an affordable price.”

Dzurak agrees: “A big challenge is to actually get near 10 qubits. Once you get to that scale, the pathway forward becomes much clearer.

Once we have shown the scientific and technical basis for 10 qubits, then our aim is to prove that you can use it to make 100, or 1,000 or 10,000.”

And this is the core of the gamble that UNSW and its six corporate and three government backers, its 12 university and research institute partners – and, in a sense, Australia – is making: that the three elegant designs for making qubit chips in silicon developed by CQC²T’s researchers will be much more feasible, more practical and easier to scale than any of the other technologies under development.

The three approaches

Professor Michelle Simmons joined UNSW in 1999, became a founding member of CQC²T, and in 2010 took over as director. Simmons now leads the UNSW-based collaboration of more than 200 researchers across seven Australian universities – UNSW, Melbourne, Queensland, Griffith, RMIT, UTS and the Australian National University – as well as Australia’s Defence Science and Technology Group. International partners include the universities of Tokyo, Wisconsin- Madison, Purdue, Singapore National and Oxford, Germany’s Max Planck and Walter Schottky institutes, and corporate partners IBM Research, Toshiba, Zyvex and Quintessence.

Along with CQC²T colleague Sven Rogge, Dzurak, Morello and Simmons are the architects of the three related yet unique approaches to quantum. Dzurak’s approach uses quantum dots, which are nano-scale semiconductor devices that straddle the behaviour of semi-conductors and discrete molecules.

In a 2015 paper in Nature, Dzurak’s team detailed the first quantum logic gate in silicon, showing quantum calculations could be performed between two qubits in silicon, leading Physics World to name it one of the top 10 advances of the year. His name is on more than 150 scientific papers and he’s a co-inventor on 11 patents.

Morello’s team was the first to demonstrate the read-out and the control of the quantum state of a single electron and a single nuclear spin in silicon. In a 2014 paper in Nature Nanotechnology, they set the record for how long a quantum superposition state can be held in the solid state, exceeding 30 seconds – 10-fold better than before. This helped him, with just 50 scientific papers under his belt, to win the Landauer-Bennett Award in 2017, “for remarkable achievements in the experimental development of spin qubits in silicon”.

Simmons’s group has developed the world’s smallest transistors and the narrowest conducting wires in silicon made with atomic precision. In a 2015 Science Advances paper, her group – working with Lloyd Hollenberg at the University of Melbourne – outlined a complete architecture for an error-corrected quantum computer, using atomic-scale qubits aligned to control lines inside a 3D design.

Simmons has published over 400 papers, has her name on seven patents, and a slew of prizes, including the Foresight Institute’s 2016 Feynman Prize for her experimental work in atomic electronics. In 2017, she was in Paris to collect the L’Oréal-UNESCO For Women in Science Award.

Rogge works closely with Simmons’s team to help understand fundamental issues related to the qubit environment. In a 2013 Nature paper, Rogge’s team detailed how to couple a silicon qubit to photons for quantum interconnects, and in a 2016 Nature Nanotechnology paper – in collaboration with the universities of Melbourne and Purdue – showed how to pinpoint a phosphorus atom in silicon with absolute atomic accuracy.

“In many ways, the quantum dots and the phosphorous atom approach, although different, are very complementary,” Morello says of UNSW’s chip designs. “Some could be made in a silicon foundry in one go, others require a serial manufacturing process. But some are almost identical.”

Three ways to make a silicon qubit. Credit: COSMOS/UNSW


The road ahead

No-one yet knows what qubit design will eventually power a universal quantum computer. Or what technological approach will create the most efficient universal quantum computer that can be scaled up, at a reasonable cost, to solve the curly problems beyond the ken of supercomputers today.

All groups are racing to achieve ‘quantum supremacy’, in which a quantum computer performs a calculation faster than any known computer could. While an important milestone, this alone will not determine the winner. That will take a decade – or more – to settle.

This article was first published in INGENUITY, Winter 2017, a publication of the Faculty of Engineering at UNSW.  Read the original story here.