For the first time, Australian
engineers have demonstrated that
they can write and manipulate the
quantum version of computer code
on a silicon microchip.
This was
done by entangling two quantum
bits with the highest accuracy
ever recorded, and it means that
we can now start to program for
the super-powerful quantum
computers of the future.
Engineers code regular computers
using traditional bits, which can
be in one of two states: 1 or 0.
Together, two bits create code
words that can be used to
program complex instructions. But
in quantum computing language
there's also the possibility for
bits to be in superposition, which
means they can be 1 and 0 at the
same time. This opens up a vastly
more powerful programming
language, but until now
researchers haven't been able to
figure out how to write it.
Now engineers from the University
of New South Wales (UNSW) in
Australia have demonstrated that
not only can they do this, but
they can do it on silicon
microchips very similar to the ones
that make up today's computers,
which means the technology will
be easy and quick to scale up.
So how exactly do you write
quantum code? It all comes down
to a phenomenon known as
quantum entanglement. When two
particles are entangled, it
basically means that the
measurement of one of them will
instantly affect the state of its
entangled particle, even if it's
thousands of kilometres away.
"This effect is famous for
puzzling some of the deepest
thinkers in the field, including
Albert Einstein, who called it
'spooky action at a distance',"
said lead researcher Andrea
Morello , from the Centre for
Quantum Computation and
Communication Technology at
UNSW. "Einstein was sceptical
about entanglement, because it
appears to contradict the
principles of 'locality', which
means that objects cannot be
instantly influenced from a
distance."
But entanglement has been
demonstrated time and time again
through something by something
known as Bell's test, which
requires engineers to violate
Bell's Inequality Principle.
Basically, Bell's Inequality
Principle sets a limit for the
amount of correlation there can
be between two classical bits –
anything above that must be
quantum entangled.
"The key aspect of the Bell test
is that it is extremely
unforgiving: any imperfection in
the preparation, manipulation and
read-out protocol will cause the
particles to fail the test," said
one of the researchers, Juan Pablo
Dehollain . "Nevertheless, we have
succeeded in passing the test, and
we have done so with the highest
'score' ever recorded in an
experiment."
In their experiment , the two
entangled particles in question
were the electron and the nucleus
of a single phosphorous atom,
which was placed inside a silicon
microchip. By entangling the two
particles, they made it so that
the state of the electron was
entirely dependent on the state of
the nucleus.
This meant that they expanded on
the four possible digital codes
that can be made with two
traditional bits (00, 01, 10, or
11) to being able to create a
much wider set of code words
with two entangled bits, such as
00+11, 00-11, 01+10 or 01-10.
"This is, in some sense, the reason
why quantum computers can be so
much more powerful," said team
member Stephanie Simmons . "With
the same number of bits, they
allow us to write a computer code
that contains many more words,
and we can use those extra words
to run a different algorithm that
reaches the result in a smaller
number of steps."
The next step is to entangle more
particles and create more complex
quantum code words, so that the
team can begin to program an
entire quantum computer. All the
other pieces are already in place,
in large part thanks to another
UNSW team, which just last
month built the first logic gate in
silicon . The material is important,
because it's something we're
already incredibly familiar with
building computers out of.
"Now, we have shown beyond an
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