Quantum supremacy: A three minute guide
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Quantum supremacy: A three minute guide

Google claims it has reached a key milestone: using a quantum computer
to complete a task that a classical computer
couldn’t manage, achieving what they call ‘quantum supremacy’. This would be the first time that a quantum
computer has definitively beaten the best conventional computer. But it’s something that physicists
have been trying to do for years. Although not everyone is convinced that a normal computer would find
this particular task impossible, it certainly seems like the
quantum processor solves it faster. The task is a calculation
that is not very useful. It was designed just to
demonstrate quantum supremacy and was made to be especially
difficult for normal computers to handle. Google’s quantum computer
is called Sycamore. It has just 53 qubits, quantum versions of the ‘bits’
that encode information in a computer. These behave completely differently to
regular bits, and are very hard to manipulate. But in theory they should allow the computer to carry out certain kinds of calculations
way faster than a classical machine. The calculation in this test was to figure
out the probability distribution of all the possible outcomes from a
quantum random number generator. Because the generator creates random
numbers using quantum operations, simulating this distribution on a classical
computer is extremely tough. But Google’s machine only needed
to set itself up like the generator, and then run those operations
a bunch of times. Sycamore produced an answer in
just 3 minutes and 20 seconds. But proving quantum supremacy, means facing
off against classical competition. For that, researchers borrowed
the supercomputing might of the Summit supercomputer at
Oak Ridge National Laboratory in Tennessee. By breaking up the problem into
smaller chunks and then extrapolating, they estimate that Summit would take 10,000
years to finish the same calculation. If true, this means a quantum computer can
do something that is, in practice, impossible on a classical machine: Quantum supremacy. But not everyone agrees. IBM has released a paper claiming that the
Summit supercomputer could actually complete the task in just 2.5 days by using a
slightly different technique. Scientists will now scrutinize
both camps’ calculations. But even if IBM is right, it’s still significant that Sycamore was so much
faster than the supercomputer. It’s the first time that this kind of
quantum speed up has ever been shown. It wouldn’t be the standard
definition of quantum supremacy, but physicists
think it’s a big deal. And although we’re still decades from harnessing
the full potential of quantum computers, and maybe years from even doing
anything particularly useful at all, this achievement tells us
that quantum computing is edging ever closer to
those goals.


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