A POWERFUL quantum computer

could crack encryption and solve

problems that classical machines

find impossible. Although

no one has yet succeeded

in building such a device,

recently we have seen a

gathering pace of progress –

so could 2022 be the year?

At the moment, efforts

are focused on an important

milestone known as quantum

supremacy: the point at which

a quantum computer is able to

complete a calculation that a

classical computer can’t, given

a reasonable amount of time.

Google was first to reach

this goal in 2019 using a device

with 54 qubits, the quantum

equivalent of regular computing

bits, to perform an essentially

useless computation known

as a random sampling

calculation. In 2021, a team

at the University of Science

and Technology of China

solved a more complex

sampling problem using

56 qubits, and later pushed

it even further with 60 qubits.

But Bob Sutor at IBM says this

game of leapfrog is an academic

achievement that is yet to

have much real impact. True

supremacy will only be achieved

when a quantum computer is

significantly better than classical

ones and is capable of solving

different problems, rather

than the random sampling

calculations currently used

as benchmarks.

He says IBM is working

towards “quantum business

advantage” – the point at

which a quantum computer

can solve genuinely useful

problems for researchers or

companies significantly faster

than classical computers can.

Sutor says this hasn’t arrived yet

and won’t during 2022, but can

be expected within the decade.

The year of a quantum

breakthrough – maybe

6

Google’s Sycamore

quantum processor is one

of the most advanced

Quantum computing

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“ Quantum

computers will

get better over

time, becoming

useful in a range

of applications”

Nir Minerbi, co-founder of

quantum software company

Classiq, is more optimistic.

He believes that 2022 will see

a demonstration of quantum

supremacy in a useful problem.

“Remember when the first

electric cars came out? They

were useful to drive to the

grocery store, but perhaps not

to drive 300 miles to drop your

kid off at college. Like electric

cars, quantum computers will

get better and better over time,

making them useful in a wider

range of applications,” he says.

There are a number of hurdles

to solving practical problems.

The first is that devices need

thousands more qubits to do

so, and these must also be more

stable and reliable than existing

ones. It is likely that researchers

will need to group them together

in clumps to work as a single

“logical qubit”. This helps with

fidelity, but will gnaw away

at improvements to scale:

thousands of logical qubits may

require millions of physical qubits.

Researchers are also working

on quantum error correction to fix

glitches when they occur. Google

announced in July 2021 that its

Sycamore processor was able

to detect and fix errors in its

superconducting qubits, but the

additional hardware needed to do

this introduced more errors than it

fixed. Researchers at the Joint

Quantum Institute in Maryland

later managed to pass through

that crucial break-even threshold

with their trapped-ion qubits.

Even so, it is early days. Scott

Aaronson at the University of

Texas at Austin says it would be

“pretty shocking” if a general-

purpose quantum computer

solved a useful problem in 2022.

“Error correction is just now

starting to work, and we don’t

even seem near the point of

protecting a single encoded qubit

for an arbitrary amount of time,

let alone doing computations

on thousands or millions of

encoded qubits,” he says.  ❚

Matthew Sparkes

1 January 2022 | New Scientist | 15