Quan­tum satel­lite tak­ing on fu­tur­is­tic chal­lenges

China Daily (Canada) - - TOP NEWS - By CHENG YINGQI chengy­ingqi@chi­nadaily.com.cn

Throw­ing coins from an air­plane and get­ting them to fall into the nar­row slot of a mov­ing piggy bank may sound im­pos­si­ble, but this, in essence, is what is be­ing done with­China’sQuan­tumS­cience Satel­lite.

On Aug 16, China launched the world’s first quan­tum satel­lite. Named af­ter the an­cient Chi­nese philoso­pher and sci­en­tist Mi­cius, the satel­lite’s launch was re­garded as a big step in build­ing a space-based quan­tum com­mu­ni­ca­tion net­work that would be vir­tu­ally un­crack­able.

“Af­ter the launch, the rocket launch­ing staff set off fire­works to cel­e­brate their suc­cess. Yet it was just the be­gin­ning for us,” said Peng Chengzhi, chief en­gi­neer of sci­ence ap­pli­ca­tions and as­sis­tant chief en­gi­neer of the satel­lite system.

Quan­tum physics is the study of mat­ter and en­ergy at sub­atomic lev­els, where the laws of tra­di­tional physics do not al­ways ap­ply.

Mi­cius is de­signed to re­lay quan­tum “keys” made up of pho­tons, or light par­ti­cles, ar­ranged in a spe­cific way. The quan­tum physics used in Mi­cius makes it im­pos­si­ble to hack en­crypted keys with­out that be­ing de­tected.

Any hack­ing would de­stroy a key made up of en­tan­gled, or paired, pho­tons.

Other ar­eas in which the satel­lite should pro­vide for more ex­per­i­men­tal op­por­tu­ni­ties in­clude long-dis­tance com­mu­ni­ca­tion us­ing pho­tons and quan­tum tele­por­ta­tion, or the the­o­ret­i­cal trans­mis­sion of tiny bits of in­for­ma­tion in an ex­act state.

Links be­tween the satel­lite and its five ground sta­tions have been es­tab­lished to en­able test­ing and ex­per­i­men­ta­tion in these ar­eas, the Chi­nese Academy of Sciences an­nounced onWed­nes­day.

“Imag­ine that we are try­ing to build a large space-ground in­te­grated quan­tum lab­o­ra­tory. The suc­cess­ful launch in Au­gust is just the first step in plac­ing the build­ing blocks in po­si­tion. Then comes the most im­por­tant step — to con­nect the quan­tum chan­nel that links the satel­lite and the ground — in which we have achieved ini­tial suc­cess in the past two months’ tests,” Peng said. “Now the space-ground quan­tum lab­o­ra­tory is tak­ing shape.”

The satel­lite, 500 kilo­me­ters high, sends in­di­vid­ual pho­tons to the ground sta­tions when it sweeps past. The difficulty of tar­get­ing the re­ceivers equals “throw­ing coins in suc­ces­sion from 10,000 me­ters above the ground into a ro­tat­ing piggy bank”, said Wang Jianyu, the quan­tum satel­lite pro­ject’s ex­ec­u­tive deputy head. “Un­like other sci­en­tific satel­lites, Mi­cius brings us more chal­lenges be­cause it is not just about send­ing sig­nals from space, it also re­quires ground-space in­ter­ac­tion.”

For ex­am­ple, the satel­lite has to send two en­tan­gled pho­tons at ex­actly the same time to two ground sta­tions and en­sure they are re­ceived by the sta­tions, lo­cated more than 1,000 kilo­me­ters apart.

Pan Jian­wei, aca­demi­cian at the Chi­nese Academy of Sciences and chief sci­en­tist for the satel­lite pro­ject, said: “When we pro­posed the quan­tum satel­lite, some of our in­ter­na­tional coun­ter­parts sug­gested we sim­plify the satel­lite’s tasks. They said that if we man­aged to suc­ceed in re­lay­ing quan­tum keys from space, it would al­ready be an amaz­ing ac­com­plish­ment. But I think we are ca­pa­ble of tak­ing on tougher chal­lenges”.

Be­sides be­ing the world’s first to achieve quan­tum com­mu­ni­ca­tion us­ing a satel­lite and Earth, Pan plans far more.

“The ex­per­i­ments onMi­cius will give an­swers to a whole lot of ques­tions. But there is more to be solved be­fore we can cre­ate a prac­ti­cal quan­tum satel­lite net­work,” he said.

“There will def­i­nitely be more sci­en­tific quan­tum satel­lites launched within the 13th Five-Year Plan (2016-20), aimed at solv­ing prob­lems Mi­cius can­not solve.”

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