The single-atom transistor

Leading quantum physicist and Quantum Technology Manager in the Archer team, Dr Martin Fuechsle discusses a fundamental link between classical and quantum computers, and the implications of atom-scale devices on the future of processing information.

Dr Fuechsle designs, fabricates, and integrates quantum devices, including having built the world’s smallest single-atom transistor. He was a member of the Australian delegation at the Lindau Meeting of Nobel Laureates and was awarded the Australian Institute of Physics Bragg Gold Medal for the most outstanding Physics PhD in Australia.

Significant progress has been made in recent years by Dr Fuechsle and the Archer team in developing the 12CQ quantum computing processor chip. Archer is developing a qubit processor chip that could potentially operate at room temperature and integrate with modern electronics.

The size of transistors has reached atomic scale, and further miniaturisation will require increasingly complex semiconductor manufacturing processes, limiting further increases in computing processing power. Quantum computing has the potential to dramatically increase information processing power.

Dr Fuechsle brought his expertise in building miniaturised quantum electronic devices to Archer and we discuss his own background, the significance of his research on the single-atom transistor, and how this relates to “quantum”.

What is a transistor — and why is that relevant to quantum computing?

A transistor is a fundamental building block of modern electronics that can serve as an electronic switch, amplifier, or voltage regulator. It is a three-terminal device: a voltage drives a current from source to drain electrodes through the semiconductor channel. The gate is the third electrode, electrically insulated from the channel. The current flowing through the semiconductor channel can be modulated by applying a voltage to the gate electrode.

In quantum computing, transistors are important because they form the basis of classical computing systems that control and read out quantum bits (qubits). Qubits are the basic unit of quantum information and are the building blocks of quantum computers. However, to create a practical quantum computer, it is necessary to interface quantum and classical computing systems. This is where transistors come in. They can be used to interface the classical control electronics with the quantum computer, allowing it to be programmed and read out.

At Archer, our 12CQ quantum chip development is utilising a unique carbon-based architecture that has the potential for practical qubit processing. We’re focused on advancing our 12CQ chip technology towards integration with mobile devices to enable more practical quantum computing technology.

You co-authored a paper that demonstrates a single atom transistor. What do you think the industry has gained from efforts to fabricate atom-sized transistors?

Prior to joining Archer my research involved looking into the fundamental limits of miniaturisation in electronics. We wanted to explore the possibilities of using individual atoms as the building blocks of electronic circuits and devices, which could potentially lead to even smaller and more efficient electronic devices.

One of the main motivations for developing a single-atom transistor was to study the behaviour of individual atoms and electrons at the nanoscale. At this scale, the behaviour of matter is governed by the principles of quantum mechanics, which can lead to strange and counterintuitive effects. By developing a transistor that operates at the single-atom level, we could study these effects and gain a deeper understanding of how they might be harnessed for practical applications.

Another motivation for developing a single-atom transistor was to explore the potential of using quantum effects for information processing. At the single-atom level, the behaviour of matter is inherently quantum mechanical, which means that it can potentially be used for quantum computing and other quantum technologies.

When did you first become interested in quantum computing and what caught your interest?

I first became interested in quantum computing when I heard about it in a lecture on solid state physics as an undergrad. Shor’s algorithm was only a few years old back then and the potential to crack an intractable problem such as prime factorisation by harnessing the peculiar properties of quantum mechanics really intrigued me.

What advice would you give those interested in working on quantum computing?

The most important thing to understand is that quantum computing inherently sits at the intersection of several disciplines, such as theoretical physics, experimental physics, electrical engineering, computer science, mathematics, and material science. So my best advice would be to keep an open mind and express a broad level of curiosity.

The full research paper detailing the research by Dr Fuechsle on a single atom transistor can be found here: https://www.nature.com/articles/nnano.2012.21

M. Fuechsle et al. A single atom transistor, Nature Nanotechnology, Volume 7, Pages 242–246 (2012).