New_Scientist_11_2_2019

6 | New Scientist | 2 November 2019

IT HAS been a bumpy start, but

a new era of computing seems

to be here. Researchers at Google

say their quantum computer

has solved a problem that

would take even the very

best conventional machine

thousands of years to crack.

The milestone, known as

quantum supremacy, represents

a long-sought stride towards

realising the immense promise

of quantum computers, devices

that exploit the strange properties

of quantum physics to speed up

certain calculations.

“This is a wonderful

achievement. The engineering

here is just phenomenal,” says

Peter Knight, a physicist at

Imperial College London.

“It shows that quantum

computing is really hard but

not impossible. It is a stepping

stone towards a big dream.”

The work was officially

published last week after a draft

was unintentionally posted on a

NASA server. It demonstrates that

a quantum processor consisting

of 54 superconducting quantum

bits, or qubits, was able to

perform a random sampling

calculation – essentially verifying

that a set of numbers is randomly

distributed – exponentially faster

than any standard computer.

Google’s Sycamore device did it

in just 3 minutes and 20 seconds,

although one of the qubits had to

be turned off as it wasn’t working

properly (Nature, doi.org/ggbnb4).

The latest version of the paper

appears to contain no significant

changes from the leaked one. For

instance, it stands by the claims

that the calculation would have

taken IBM’s Summit, the world’s

most powerful supercomputer,

some 10,000 years.

IBM has already pushed back

on this, insisting that with some

clever classical programming its

machine can solve the problem in

2.5 days. Indeed, IBM, which has its

own 53-qubit quantum computer,

prefers a higher threshold

for quantum supremacy. This

explains its argument that Google

hasn’t yet reached the milestone.

“Classical computers have such

a large suite of things built into

them that if you don’t utilise every

single thing you leave yourself

open for a tweaked classical

algorithm to beat your quantum

one,” says Ciarán Gilligan-Lee

at University College London.

In this case, the IBM researchers

say that Google didn’t fully

consider the supercomputer’s

storage potential. Taking that

into account, they calculated that

it would actually be reasonable

for a classical supercomputer

to do this calculation.

“An ideal simulation of the

same task can be performed on

a classical system in 2.5 days and

with far greater fidelity” when

the memory is taken advantage

of, the IBM team wrote in a

blog post. “This is in fact a

conservative, worst-case

estimate, and we expect that

with additional refinements the

classical cost of the simulation

can be further reduced.”

Tech giant tussle

Google has hit back at these

claims. “We’re looking forward

to when people actually run

the idea on Summit and check it

and check our data because that’s

part of the scientific process – not

just proposing it but actually

running it and checking it,”

said John Martinis, who led

Google’s work, during a press

conference last week.

As quantum computers

improve over time, so do classical

News Quantum computing special report

Quantum breakthrough

Google reigns supreme

For the first time, quantum computers are starting to flex their muscles, 

report Daniel Cossins and Leah Crane

1980

Paul Benioff

describes the

first quantum

mechanical model

of a computer,

showing that

quantum computers

are theoretically

possible

1985

David Deutsch

develops the idea of

a universal quantum

computer: a way

to mathematically

understand what

is possible on a

quantum computer

1994

Peter Shor develops

“Shor’s algorithm”,

which would allow a

quantum computer

to factor large

numbers much

faster than the best

classical algorithm

(see page 9)

1995

Several researchers

independently

propose the first

quantum error-

correction methods

to automatically

fix errors that can

easily arise in a

quantum computer

1997

Quantum

teleportation,

the transmission

of quantum

information

from one place

to another, is first

demonstrated for

single photons

1998

Researchers at the

University of Oxford

run a quantum

algorithm for the

first time, on a

2-qubit quantum

computer

“For those of us working in
science and technology, it’s
the ‘hello world’ moment
we’ve been waiting for”
Google CEO Sundar Pichai

Google’s Sycamore

quantum computer

GOOGLE