Harnessing and controlling the spin
of electrons is the goal
of quantum computing.  
Where a conventional bit
is either one or zero,
the quantum bit,
based on the spin of
an electron as it
orbits an atom,
is a combination of a one state
and zero state at the same time.  
This quantum bit, or qubit,
opens a whole new era of programming
and promises to solve problems
that conventional computers can't.  
But to be effective, you need many
qubits and you have to be able
to control a spin of each one. 
I guess one of the critical problems
we have is these qubits are
very very close together
so we've got a beautiful atomic system
but they you know, literally
tens of nano metres apart
and so how do you address one
without affecting all of them
at the same time and any kind of
you know, electrode that you put down
is going to affect all of them
in the same kind of electric field
or magnetic field.  
And so that's really the critical part
of this paper, how do we individually
address those individual electron spins
on these atoms that are so close together?
But now a team at the
University of New South Wales in Sydney
has published a paper in
Nature Communications Magazine
showing that if the electron is bound to
a different number of phosphorus atoms
than its neighbouring electron,
each will respond separately
to tuned electro-magnetic fields. 
The beauty about phosphorus clusters
is that a single electron bound to
one of these clusters will have
a different rotation frequency.  
So, now you can choose the right frequency
to only rotate the electron spin
which is bound to the phosphorus cluster
but at the same time, you do not rotate
electron spin which is hosted by
the single phosphorus donor.  
And vice versa.  
You can also choose the frequency
to rotate the electron spin
which is bound to the
single phosphorus atom
and you do not rotate the electron spin
which is housed by the phosphorus cluster.
Importantly, the UNSW team
in collaboration with
Sandia National Laboratories
has shown that the electron spin
is not degraded by the presence of
multiple phosphorus atoms.
And that we did by realising this device
in our laboratories
and it is such a cluster of
about four phosphorus donors
and next to it, we fabricated a readout 
architecture and with this readout
architecture we were able to measure
the lifetime of the spin qubit
and we found the lifetime
of the spin qubit is still very long
compared to that of a single donor. 
So this is a really unique
and nice method about how to
address individual qubits
and I think when you go to
long term quantum computing
it's the kind of thing
that we're going to really have to
understand how to do well. 
