Has the age of quan­tum com­put­ing ar­rived?


Ever since Charles Bab­bage’s con­cep­tual, un­re­alised An­a­lyt­i­cal En­gine in the 1830s, com­puter science has been try­ing very hard to race ahead of its time. Par­tic­u­larly over the last 75 years, there have been many as­tound­ing de­vel­op­ments – the first elec­tronic pro­grammable com­puter, the first in­te­grated cir­cuit com­puter, the first mi­cro­pro­ces­sor.

But the next an­tic­i­pated step may be the most revo­lu­tion­ary of all.

Quan­tum com­put­ing is the tech­nol­ogy that many sci­en­tists, en­trepreneurs and big busi­nesses ex­pect to pro­vide a, well, quan­tum leap into the fu­ture. If you’ve never heard of it there’s a help­ful video do­ing the so­cial me­dia rounds that’s got a cou­ple of mil­lion hits on YouTube. It fea­tures the Cana­dian prime min­is­ter, Justin Trudeau, de­tail­ing ex­actly what quan­tum com­put­ing means.

Trudeau was on a re­cent visit to the Perime­ter In­sti­tute for The­o­ret­i­cal Physics in Water­loo, On­tario, one of the world’s lead­ing cen­tres for the study of the field. Dur­ing a press con­fer­ence there, a re­porter asked him, half-jok­ingly, to ex­plain quan­tum com­put­ing.

Quan­tum me­chan­ics is a con­cep­tu­ally coun­ter­in­tu­itive area of science that has baf­fled some of the finest minds – as Al­bert Ein­stein said “God does not play dice with the uni­verse” – so it’s not some­thing you ex­pect to hear politi­cians hold­ing forth on.

Throw it into the con­text of com­put­ing and let’s just say you could eas­ily make Zac Gold­smith look like an ex­pert on Bol­ly­wood. But Trudeau rose to the chal­lenge and gave what many science ob­servers thought was a text­book ex­am­ple of how to ex­plain a com­plex idea in a sim­ple way.

The con­cept of quan­tum com­put­ing is rel­a­tively new, dat­ing back to ideas put for­ward in the early 1980s by the late Richard Feyn­man, the bril­liant Amer­i­can the­o­ret­i­cal physi­cist and No­bel lau­re­ate.

He con­cep­tu­alised the pos­si­ble im­prove­ments in speed that might be achieved with a quan­tum com­puter. But the­o­ret­i­cal physics, while a nec­es­sary first step, leaves the real brain­work to prac­ti­cal ap­pli­ca­tion.

With nor­mal com­put­ers, or clas­si­cal com­put­ers as they’re now called, there are only two op­tions – on and off – for pro­cess­ing in­for­ma­tion. A com­puter “bit”, the small­est unit into which all in­for­ma­tion is bro­ken down, is ei­ther a “1” or a “0”.

And the com­pu­ta­tional power of a nor­mal com­puter is de­pen­dent on the num­ber of bi­nary tran­sis­tors – tiny power switches – that are con­tained within its mi­cro­pro­ces­sor.

Back in 1971 the first In­tel pro­ces­sor was made up of 2,300 tran­sis­tors. In­tel now pro­duce mi­cro­pro­ces­sors with more than 5bn tran­sis­tors. How­ever, they’re still lim­ited by their sim­ple bi­nary op­tions. But as Trudeau ex­plained, with quan­tum com­put­ers the bits, or “qubits” as they are known, af­ford far more op­tions ow­ing to the un­cer­tainty of their phys­i­cal state.

In the mys­te­ri­ous sub­atomic realm of quan­tum physics, par­ti­cles can act like waves, so that they can be par­ti­cle or wave or par­ti­cle and wave. This is what’s known in quan­tum me­chan­ics as su­per­po­si­tion. As a re­sult of su­per­po­si­tion a qubit can be a 0 or 1 or 0 and 1.

That means it can per­form two equa­tions at the same time. Two qubits can per­form four equa­tions. And three qubits can per­form eight, and so on in an ex­po­nen­tial ex­pan­sion. That leads to some

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