The Economist Asia - 24.02.2018

The EconomistFebruary 24th 2018 Science and technology 69

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ALCULATING machines that run on

quantum bits (known asqubits, for

short) are, by some accounts, the future of

computation. Quantum computers have

the theoretical advantage that they can

solve with ease certain mathematical pro-

blems, such as the factorisation of large

numbers, which are hard or impossible for

classical machines. This is possible thanks

to a qubit’s ability to remain, through the

peculiarities of quantum mechanics, in

many quantum states simultaneously. The

more qubits a computer has, the more

mind-bogglingly gigantic are the calcula-

tions it can handle. Finance, medicine,

chemistry and artificial intelligence are

thus all expected to be transformed by

quantum computing.

And where the future is, there surely

will Google be also. The firm sets great

store by its quantum-computing project,

which it calls Project Bristlecone. This is in-

tended to develop a “quantum-supremacy

device”, ie, one that is palpably and prov-

ably faster than a traditional computer of

equivalent size atsolving particular math-

ematical problems. Google is currently

preparing such a device, which will have

49 qubits. Itis rumoured thatthis will be

ready for demonstration before the year is

out. Though not confirming such rumours,

John Martinis, Google’s quantum-comput-

ing boss, told the AAASmeeting about

some of the problems involved in doing so.

Leadership in the quantum-computing

race, Dr Martinis said, is typically mea-

sured in terms of the number of qubits that

a machine can handle. Less attention is

paid to those machines’ error rates. Since

the people building such experimental

machines are usually physicists, rather

than engineers, they typically cite their

best measurementswhen reportingqubit

error rates, in order to show the machine’s

capability. That number is of little interest

to Dr Martinis and his team, though. They

are thinking like engineers, attempting to

build a robust, working device. In this case,

Dr Martinis says, it is the worst error, not

the slightest, that is important.

Project Bristlecone’s main concern is

the quality ofthe qubits. The theoretical

ability to beat a classical computer is of lit-

tle use if the hardware that serves as the

physical representations of those calcula-

tions is misfiring or dodgy.

At the moment, that is sometimes the

case. Preparing and maintainingqubits is a

delicate and fiddly process, akin to classi-

Quantum computing

Quality over

quantity

AUSTIN

If quantum computers are to be useful,

they must first be reliable

A

ROUND 1936 three neurologists atHar-

vard Medical School raided the medi-

cine cabinet, filling their boots with mor-

phine, barbiturates, ethers and even cobra

venom. They injected those substances

into (apparently) willing volunteers and

cemented primitive electrodes to their

scalps and earlobes. They also collared a

drunk and wired him up. With pen and pa-

per, they then recorded how the electrical

signals in their volunteers’ brains changed

as the drugs began to take hold.

This kind of gonzo science might meet a

touch of resistance from the institutional

review board if proposed today, but the

work of Gibbs, Gibbs and Lennox still

stands. The trio showed, without meaning

to, that sedatives lower the activity of the

brain through several clear stages, and that

each stage is observable in that organ’s

electrical readings. Their results have been

refined over the years, of course, to the ex-

tent that Emery Brown, a successor of

theirs at Harvard, now thinks, as he told

the AAASmeeting, that statistical analysis

of such electroencephalography (EEG) sig-

nals has become so good that it can be used

to make anaesthesia safer and better.

The EEG of a conscious brain shows no

striking features, just low-amplitude and

seemingly uncorrelated ups and downs in

the frequency of oscillations in the brain’s

electric field. That is because the brain’s

neurons are firing independently of one

another as they go about the various tasks

that render their owner conscious. Then

(as the Harvard trio found) as the patient

goes under the oscillations smooth out,

deepening into a stark, uniform wave

which vibrates ten times a second. The

drug has tripped the neurons into singing

from the same hymn sheet. Their unified

song takes over from the cacophony of a

conscious brain, and the patient is out.

That, Dr Brown believes, gives anaes-

thetists a better way to assess how deeply

someone is under than measuring blood

pressure and heart rate. He regularly uses

brain waves clinically. In a recent opera-

tion, for example, he was able to adminis-

ter a third of the normal dose of an anaes-

thetic called propofol to an 81-year-old

cancer patient, monitoring her brain

waves to ensure that she was deeply under

at all times. Indeed, he thinks he may be

able to automate the whole process, and

has designed a machine which adjusts the

dose in response to brainwave changes.

He also believes that the potential for

using EEG to understand unconscious

brainwaves goes beyond the operating ta-

ble. Sleeping pills, for instance, do not so

much aid sleep as sedate their recipient. Dr

Brown thinks insomniacs might be guided

into true sleep through a more precise ex-

amination of their brain activity, and the

application of commensurate drugs.

Moreover, true successor to Gibbs,

Gibbs and Lennox that he is, Dr Brown re-

veals his own gonzo side when he says his

understanding ofEEGreadouts is such that

he believes he could safely place someone

into, and then retrieve him from, a

“locked-in” state—one in which a person is

fully aware of his surroundings, but inca-

pable of any movement or action. When

your correspondent offered himself as a

test subject, only partially in jest, Dr Brown

flashed an arch grin, before sombrely ex-

plaining that such an experiment would

be beyond the tolerance of modern review

boards, too. 7

Unconsciousness

Going under

AUSTIN

Tracking the brain’s electrical activity

can make anaesthesia safer

Watching the waves

tem, including the heart. Dr Garry, too, is

then able to persuade human stem cells to

grow into organ cells—in his case heart

cells—though at the moment they form

only a small proportion of the cells in the

resultant embryonic hearts.

In their quests for pancreatic cells, Dr

Nakauchi and Dr Ross have encountered

similar problems of rarity. But these are

early days. Dr Garry, whose laboratory is

now producing two or three pig-human fe-

tuses a week, is studying those fetuses to

try to understand why it is that in some

only one heart cell in 100,000 is human

while in other fetuses the number is one in

100. If he can discoverthe underlying prin-
     ciple, then the aim of replacing pig cardiac
     cells entirely with human ones will have
     come closer. 7