What are quantum computers and how do they
work?
Google, IBM and a handful of startups are
racing to create the next generation of supercomputers.
Quantum computers, if they ever get started,
will help us solve problems, like modelling
complex chemical processes, that our existing
computers can't even scratch the surface of.
But the quantum future isn't going to come
easily, and there's no knowing what it'll
look like when it does arrive.
At the moment, companies and researchers are
using a handful of different approaches to
try and build the most powerful computers
the world has ever seen.
Here's everything you need to know about the
coming quantum revolution.
What is quantum computing?
Quantum computing takes advantage of the strange
ability of subatomic particles to exist in
more than one state at any time.
Due to the way the tiniest of particles behave,
operations can be done much more quickly and
use less energy than classical computers.
In classical computing, a bit is a single
piece of information that can exist in two
states – 1 or 0.
Quantum computing uses quantum bits, or 'qubits'
instead.
These are quantum systems with two states.
However, unlike a usual bit, they can store
much more information than just 1 or 0, because
they can exist in any superposition of these
values.
Google's D-Wave supercomputer
D-Wave
"The difference between classical bits and
qubits is that we can also prepare qubits
in a quantum superposition of 0 and 1 and
create nontrivial correlated states of a number
of qubits, so-called 'entangled states',"
says Alexey Fedorov, a physicist at the Moscow
Institute of Physics and Technology.
A qubit can be thought of like an imaginary
sphere.
Whereas a classical bit can be in two states
– at either of the two poles of the sphere
– a qubit can be any point on the sphere.
This means a computer using these bits can
store a huge amount more information using
less energy than a classical computer.
How far away are quantum computers?
Until recently, it seemed like Google was
leading the pack when it came to creating
a quantum computer that could surpass the
abilities of conventional computers.
In a Nature article published in March 2017,
the search giant set out ambitious plans to
commercialise quantum technology in the next
five years.
Shortly after that, Google said it intended
to achieve something it’s calling ‘quantum
supremacy’ with a 49-qubit computer by the
end of 2017.
Now, quantum supremacy, which roughly refers
to the point where a quantum computer can
crunch sums that a conventional computer couldn’t
hope to simulate, isn’t exactly a widely
accepted term within the quantum community.
Those sceptical of Google’s quantum project
– or at least the way it talks about quantum
computing – argue that supremacy is essentially
an arbitrary goal set by Google to make it
look like it’s making strides in quantum
when really it’s just meeting self-imposed
targets.
Whether it’s an arbitrary goal or not, Google
was pipped to the supremacy post by IBM in
November 2017, when the company announced
it had built a 50-qubit quantum computer.
Even that, however, was far from stable, as
the system could only hold its quantum microstate
for 90 microseconds, a record, but far from
the times needed to make quantum computing
practically viable.
Just because IBM has built a 50-qubit system,
however, doesn’t necessarily mean they’ve
cracked supremacy and definitely doesn’t
mean that they’ve created a quantum computer
that is anywhere near ready for practical
use.
Where IBM has gone further than Google, however,
is making quantum computers commercially available.
Since 2016, it has offered researchers the
chance to run experiments on a five-qubit
quantum computer via the cloud and at the
end of 2017 started making its 20-qubit system
available online too.
But quantum computing is by no means a two-horse
race.
Californian startup Rigetti is focusing on
the stability of its own systems rather than
just the number of qubits and it could be
the first to build a quantum computer that
people can actually use.
D-Wave, a company based in Vancouver, Canada,
has already created what it is calling a 2,000-qubit
system although many researchers don’t consider
the D-wave systems to be true quantum computers.
Intel, too, has skin in the game.
In February 2018 the company announced that
it had found a way of fabricating quantum
chips from silicon, which would make it much
easier to produce chips using existing manufacturing
methods.
What can quantum computers do that normal
ones can’t?
Quantum computers operate on completely different
principles to existing computers, which makes
them really well suited to solving particular
mathematical problems, like finding very large
prime numbers.
Since prime numbers are so important in cryptography,
it’s likely that quantum computers would
quickly be able to crack many of the systems
that keep our online information secure.
Because of these risks, researchers are already
trying to develop technology that is resistant
to quantum hacking, and on the flipside of
that, it’s possible that quantum-based cryptographic
systems would be much more secure than their
conventional analogues.
Researchers are also excited about the prospect
of using quantum computers to model complicated
chemical reactions, a task that conventional
supercomputers aren’t very good at all.
In July 2016, Google engineers used a quantum
device to simulate a hydrogen molecule for
the first time, and since them IBM has managed
to model the behaviour of even more complex
molecules.
Eventually, researchers hope they’ll be
able to use quantum simulations to design
entirely new molecules for use in medicine.
But the holy grail for quantum chemists is
to be able to model the Haber-Bosch process
– a way of artificially producing ammonia
that is still relatively inefficient.
Researchers are hoping that if they can use
quantum mechanics to work out what’s going
on inside that reaction, they could discover
new ways to make the process much more efficient.
