Making Quantum Truly Scalable

Diraq, the recently incorporated start-up company from the Dzurak Group at UNSW, are the global leaders in developing silicon metal-oxide-semiconductor (SiMOS) quantum-dot qubit devices for quantum computing.

In 1964, Richard Feynman, Nobel Laureate and the father of nanotechnology, said, ‘I think I can safely say that nobody really understands quantum mechanics.’ However, he later proposed harnessing it to build a more powerful kind of computer.

These computers are machines that use quantum phenomena to store data and perform computations. Quantum computers are predicted to solve many currently intractable problems, such as drug design and climate modelling. Long dismissed as science fiction, today we are in a race to build the hardware that will make quantum computers a reality.

Traditional transistors composed of silicon metal oxide semiconductors (SiMOS) control tiny currents of electrons. An applied gate voltage either allows current to flow from source to drain or not. Thus, a transistor acts as a binary switch in a circuit, existing in a charged or un-charged state. A charged state is considered a ‘0’, and an un-charged state a ‘1’. Computers have become faster, smaller and more efficient over time as transistors have become smaller, allowing more transistors on a computer chip. The processors in mobile phones and tablets contain billions of transistors on a single chip.

Innovative technology developed by the Dzurak Group Silicon Quantum Dot Qubit research programme at UNSW has successfully created the world’s first SiMOS-based quantum processor. Their quantum transistor controls a single electron – forming the fundamental unit of quantum information, the qubit.

By manipulating the surface gate voltage, a single electron is confined within a quantum dot. The spin of the electron, a property comparable to rotation, creates a small magnetic field. The binary nature of electron spin – clockwise (spin-up) or counterclockwise (spin-down) – makes spin an ideal candidate for the encoding of information.

Within an applied magnetic field, the energy of the spin-up state becomes higher than spin-down. This energy difference enables read-write memory. We can verify the electron’s energy level, thus ‘reading’ the current state of spin (spin-down is 1; spin-up is 0) and can ‘write’ by flipping the electron’s spin state with a microwave signal of sufficient energy.

If you place two quantum bits side by side, microwave and voltage signals control the qubits and make them interact. In addition, the state of one qubit depends on the state of its neighbour. Letting these qubits interact creates logic gates capable of performing basic Boolean operations (AND, OR, NOT, etc.).

In the recent years, the Dzurak Group has achieved high fidelity single-qubit and two-qubit gates in silicon. More recently, they have explored the potential of ‘global’ spin qubit control in SiMOS quantum dot arrays to scale up the number of qubits to billions. Their revolutionary technology is compatible with the existing semiconductor manufacturing techniques – the only viable approach to scale up the number of qubits to billions for useful commercial applications.

The involvement of ANFF has been crucial to the creation of the first SiMOS quantum computing chip. The fabrication of silicon qubit devices is performed fully in-house in the ANFF-NSW cleanrooms. Without access to ANFF’s suite of state-of-the-art equipment and processes, the Dzurak Group’s cutting-edge research and output rate would not be possible. In particular, the capability to grow high-quality silicon dioxide in high temperature furnaces plus access to nanometre-precision electron beam lithography has enabled them to construct world-class qubit devices.

This year, culminating from two decades of research, Prof. Andrew Dzurak has launched a start-up company – Diraq – which aims to redefine scalable quantum computing and bring practical commercial applications to the world via billions of qubits on a single chip.

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