Silicon back in the race for quantum computers

6 August 2008

in 2008

The odds that a futuristic quantum computer will be built of silicon have received a boost, thanks to new technology recently invented by researchers in the Centre for Quantum Computer Technology (CQCT).

They’ve made a silicon chip that can control and observe individual electrons and they are now using this chip to make quantum test chips.

The potential speed and power of a quantum computer is known to far exceed even the biggest supercomputers of today.  What is still unclear though is the best method to build one.

Teams around the world are in a race to create the first quantum computer – there are ten or more competing technologies being investigated including photonics (light), nuclear magnetic resonance, superconducting materials, ion traps as well as silicon technology.

One of the advantages of silicon technology is that quantum chips could be integrated easily with our current computer chips – that makes it considerably easier to build a large scale quantum computer.

Susan Angus and her CQCT colleagues, working at the University of New South Wales, were able to isolate a few electrons on a nano-scale silicon island and then controllably add or remove electrons just one at a time. They have also used this new technique to make a fast and sensitive detector in silicon, which is able to sense the movement of a just a single electron nearby.

“Building a quantum computer involves perfect control of the most fundamental properties of our universe. Controlling and observing individual electrons is an important step towards that goal,” says Susan.

A quantum computer is not just a faster, smaller version of current machines, it will operate using the strange principles of quantum physics. One of the key features is that instead of using the binary system—where the computer uses  tiny switches or ‘bits’ that are either on or off —the basic units of a quantum computer, the ‘qubit’, can be both on and off simultaneously.

“It is impossible to predict the impact that this incredibly powerful new form of computing will have – just like it was difficult to predict the impact that ordinary computers have had on our society.  We do know though there are a number of jobs that a quantum computer will be able to do much more quickly – for example, it will speed up drug design, genetic testing and climate analysis, just to name a few,” says Susan.

“It’s exciting work,” says Susan, now a postdoctoral fellow at the University of Melbourne node of the CQCT, “because we’re working at the very edge of our knowledge of the universe and of matter.  We’re trying to build technology for the future.” Susan Angus is one of 16 early-career scientists chosen for Fresh Science, a national program sponsored by the Federal and Victorian governments. She is presenting her research to the public for the first time.

Her work is the subject of a provisional patent and has been published in Nano Letters and Applied Physics Letters.


Susan Angus is based at The Centre for Quantum Computer Technology – an Australian multi-university collaboration undertaking research on the fundamental physics and technology of building, at the atomic level, a solid state quantum computer in silicon together with other high potential implementations. The objective is underpinned by a vigorous semiconductor research program that includes a sophisticated quantum measurement capability at ultra-low temperatures. Read more about the centre here.


Gate-Defined Quantum Dots in Intrinsic Silicon
Susan J. Angus,* Andrew J. Ferguson, Andrew S. Dzurak, and Robert G. Clark
Australian Research Council Centre of Excellence for Quantum Computer Technology, University of New South Wales, Sydney, Australia

We report the fabrication and measurement of silicon quantum dots with tunable tunnel barriers in a narrow-channel field-effect transistor. Low-temperature transport spectroscopy is performed in both the many-electron (~100 electrons) regime and the few-electron (~10 electrons) regime. Excited states in the bias spectroscopy provide evidence of quantum confinement. These results demonstrate that depletion gates are an effective technique for defining quantum dots in silicon.


A silicon radio-frequency single electron transistor
S. J. Angus, A. J. Ferguson, A. S. Dzurak, and R. G. Clark
Australian Research Council Centre of Excellence for Quantum Computer Technology, The University of New South Wales, Sydney, New South Wales 2052, Australia

We report the demonstration of a silicon radio-frequency single electron transistor. The island is defined by electrostatically tunable tunnel barriers in a narrow channel field effect transistor. Charge sensitivities of better than 10 µe/sqrt(Hz) are demonstrated at megahertz bandwidth. These results demonstrate that silicon may be used to fabricate fast, sensitive electrometers. ©2008 American Institute of Physics


Click on image for high resolution image for download

Susan (pictured far left) and colleagues at the Semiconductor Nanofabrication Facility at UNSW.Photo: Romeo Viglino.

An electron microscope image of one silicon quantum chip. Similar to the conventional CMOS chips that power our computers today, this silicon chip has already demonstrated its potential for the quantum computers of tomorrow.The bright lines are metal (aluminium) gates on the surface of the chip that control the location of electrons in the silicon underneath.Photo: Susan Angus, Centre for Quantum Computer Technology.

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