Engineers at the University of New South Wales (UNSW) have published
a complete design for a quantum computer chip, that can be manufactured using
mostly standard industry processes and components.
The new chip design, published
in the journal Nature Communications, details a novel architecture
that allows quantum calculations to be performed using existing semiconductor
components, known as CMOS (complementary metal-oxide-semiconductor) – the basis
for all modern chips. It’s the first attempt to integrate into a single chip
all of the conventional silicon circuitry needed to control and read the
millions of qubits needed for quantum computing.
The design was devised by Professor Andrew
Dzurak, director of the Australian
National Fabrication Facility at the University of New South Wales
(UNSW), and Dr. Menno
Veldhorst, lead author of the paper who was a research fellow at UNSW when
the conceptual work was done.
A quantum computer exponentially expands the vocabulary of
binary code used in modern computers’. At the subatomic level, the laws of
classical physics no longer apply. Particles can exist in more than one
state at a time. Quantum computing utilises these so-called spooky quantum-mechanical
phenomena, superposition and entanglement, to perform operations on data.
Entanglement occurs when pairs or groups of particles are generated or interact
in ways such that the quantum state of each particle (such as the polarisation
of a photon) cannot be described independently of the others, even when the
particles are separated by a large distance, while superposition states that
any two (or more) quantum states can be added together and the result will be
another valid quantum state.
A classical bit can be in one of two states, 0 or 1, whereas
a single qubit or quantum bit can represent a 1, a 0 or any quantum
superposition of those two qubit states. This would allow a universal quantum
computer to be millions of times faster than any conventional computer when
solving a range of important problems.
For some challenging problems they could find solutions in
days, or even hours, which today’s fastest supercomputers would take millions
of years to solve. But to solve these complex problems like cancer and global
challenges like climate change, a useful universal quantum computer will need a
large number of qubits, possibly millions, packed together and integrated like
in modern microprocessor chips.
The press release from UNSW explains that there are at least
five major quantum computing approaches being explored worldwide: silicon spin
qubits, ion traps, superconducting loops, diamond vacancies and topological
qubits (this backgrounder
document provides brief introductions to the different approaches). UNSW’s
design is based on silicon spin qubits. But there has been no clear pathway
till now to scaling the number of quantum bits up to the millions needed,
without the computer becoming huge a system requiring bulky supporting
equipment and costly infrastructure.
Moreover, all known types of qubits are fragile, and even
tiny errors can be quickly amplified into wrong answers.
The new design from the UNSW researchers incorporates
conventional silicon transistor switches to ‘turn on’ operations between qubits
in a vast two-dimensional array, using a protocol similar to that used to
select bits in a conventional computer memory chip. By selecting electrodes
above a qubit, a qubit’s spin can be controlled, which stores the quantum
binary code of a 0 or 1. And by selecting electrodes between the qubits,
two-qubit logic interactions, or calculations, can be performed between qubits.
The design also incorporates error-correcting codes which
employ multiple qubits to store a single piece of data. Our chip blueprint
incorporates a new type of error-correcting code designed specifically for spin
qubits, and involves a sophisticated protocol of operations across the millions
Prof. Dzurak, who is also a Program Leader at Australia’s Centre of Excellence for Quantum Computation and
Communication Technology (CQC2T), said, ““We often think of landing on
the Moon as humanity’s greatest technological marvel. But creating a
microprocessor chip with a billion operating devices integrated together to
work like a symphony – that you can carry in your pocket! – is an astounding
technical achievement, and one that’s revolutionised modern life. With quantum
computing, we are on the verge of another technological leap that could be as
deep and transformative. But a complete engineering design to realise this on a
single chip has been elusive. I think what we have developed at UNSW now makes
that possible. And most importantly, it can be made in a modern semiconductor
Veldhorst, now a team leader in quantum technology at QuTech – a collaboration between Delft
University of Technology and TNO, the Netherlands Organisation for Applied
Scientific Research – said the power of the new design is that, for the first
time, it charts a conceivable engineering pathway toward creating millions of
quantum bits, or qubits.
Other CQC2T researchers involved in the design published in
the Nature Communications paper were Henry Yang and Gertjan
Eenink, the latter of whom has since joined Veldhorst at QuTech.
Only two years ago, in a paper in Nature, Prof. Dzurak
and Dr. Veldhorst showed, for the first time, how quantum logic calculations
could be done in a real silicon device, with the creation of a two-qubit logic
gate – the central building block of a quantum computer.
“Those were the first baby steps, the first demonstrations
of how to turn this radical quantum computing concept into a practical device
using components that underpin all modern computing. Our team now has a
blueprint for scaling that up dramatically,” said Mark Hoffman, UNSW’s Dean of
“We’ve been testing elements of this design in the lab, with
very positive results. We just need to keep building on that – which is still a
hell of a challenge, but the groundwork is there, and it’s very encouraging. It
will still take great engineering to bring quantum computing to commercial
reality, but clearly the work we see from this extraordinary team at CQC2T puts
Australia in the driver’s seat,” he added.
The UNSW team has struck a A$83 million deal between UNSW,
Telstra, Commonwealth Bank and the Australian and New South Wales governments to
develop, a 10-qubit prototype silicon quantum integrated circuit by 2022 –
the first step in building the world’s first quantum computer in silicon.
In August, the partners launched Silicon Quantum Computing
Pty. Ltd., Australia’s first quantum computing company, to advance the
development and commercialisation of the team’s unique technologies. The NSW
Government pledged AU$8.7 million, UNSW AU$25 million, the Commonwealth Bank AU$14
million, Telstra AU$10 million and the Australian Government AU$25 million.