A team of Australian engineers
and physicists have claimed a world first,
the creation of a single atom quantum bit in a silicone chip.
The work, published in Nature Magazine, is the fundamental requirement
for a revolutionary piece of hardware, the quantum computer. Team leaders, Doctor Andrea Morello
and Professor Andrew Dzurak and the main experimental author,
Jared Pla, are based at The University of New South Wales
in Sydney. Modern computers store information
as bits which can be either zero or one
to create a binary code. These bits are realised
using transistors or other devices on a silicone chip. Now the power of modern computing
comes from the fact that over the last fifty years,
it’s been possible to cram more and more of these silicone transistors
so there’s now over a billion of these on a single
square centimetre of silicone on a chip.
Now imagine you can make a bit that can be in the zero
and the one state at the same time. That’s called a quantum bit, or qubit,
and the simplest example in nature would be just a single electron.
It has a magnetic dye pool called the spin which is like
the needle of a compass, but because it’s a quantum needle,
it can be pointing up and down at the same time.
If you can make a computer that uses that, then you can program it
in a completely different way and you can solve certain problems
that are otherwise impossible to solve on normal computers.
For example, simulating and understanding molecules and complicated drugs for instance.
So you can actually design them on a computer
instead of having to find them by trial and error.
So to build a large scale functioning quantum computer,
you need four basic elements. First you need to be able to
read information on the quantum bit, then write information on a qubit,
then to take pairs of qubits and perform operations between them,
and finally, transport information around the quantum processor
to perform complex calculations. To build a qubit, you must first
insert a single phosphorus atom into a silicone chip,
then build tiny electrodes just thirty nanometres wide above it. Each wire is three thousand times
smaller than the width of a human hair. Adding a small voltage
to the electrode above the phosphorus ion forces an electron to cross the gap
and orbit the phosphorus.
That’s the initialisation stage and the qubit is in a logic zero state. What we do to write information
on the electron spin is to radiate it with microwaves.
The spin absorbs these microwaves and then begins to rotate
around this sphere from down to up. It can’t stay tied to the
phosphorus atom at spin up so it drops back into the electron pool.
This switches the transistor on which corresponds to reading
a logic one state. What we’ve done now is
to demonstrate the first two steps for a quantum computer, to read
and to write information on a single quantum bit represented by
an electron spin but this is still done with the same technology
used for normal silicone chips. The electron is attached to an atom
that’s implanted in the silicone a nd the quantum information encoded on it
is read out with a silicone transistor j ust fabricated next to the electron. Silicone microelectronics
and nano-electronics underpins all of the information age at the moment
and if you can make a quantum computer using silicone, then you’ve got
a fantastic advantage in terms of manufacturability. So the fact that we’ve now
demonstrated a quantum bit in a system that uses
effectively silicone transistors to read it out, is a remarkable step.
And it is going to very significantly accelerate the work in silicone. I’m truly amazed every day
that I step into the lab I mean, on a daily basis
I get to interact with this single electron which belongs to
a single atom. We really are controlling nature
at its most fundamental level and being able to demonstrate
the potential of the system for quantum computing,
to me it’s just icing on the cake.