研究人员通过调谐光学谐振器来控制透明度

时间:2020-03-25 18:38 来源:seo 作者:杏鑫 点击量:

研究人员通过调谐光学谐振器来控制透明度

方法在量子计算、通信等领域都有分支。

In+the+quantum+realm%2c+under+some+circumstances+and+with+the+right+interference+patterns%2c+light+can+pass+through+opaque+media.%0aThis+feature+of+light+is+more+than+a+mathematical+trick%3b+optical+quantum+memory%2c+optical+storage+and+other+systems+that+depend+on+interactions+of+just+a+few+photons+at+a+time+rely+on+the+process%2c+called+electromagnetically+induced+transparency%2c+also+known+as+EIT.+%26nbsp%3b%0aBecause+of+its+usefulness+in+existing+and+emerging+quantum+and+optical+technologies%2c+researchers+are+interested+in+the+ability+to+manipulate+EIT+without+the+introduction+of+an+outside+influence%2c+such+as+additional+photons+that+could+perturb+the+already+delicate+system.+Now%2c+researchers+at+the+McKelvey+School+of+Engineering+at+Washington+University+in+St.+Louis+have+devised+a+fully+contained+optical+resonator+system+that+can+be+used+to+turn+transparency+on+and+off%2c+allowing+for+a+measure+of+control+that+has+implications+across+a+wide+variety+of+applications.%0aThe+group+published+the+results+of+the+research%2c+conducted+in+the+lab+of+Lan+Yang%2c+the+Edwin+H.+%26amp%3b+Florence+G.+Skinner+Professor+in+the+Preston+M.+Green+Department+of+Electrical+%26amp%3b+Systems+Engineering%2c+in+a+paper+titled+Electromagnetically+Induced+Transparency+at+a+Chiral+Exceptional+Point+in+the+January+13%2c+2020%2c+issue+of+Nature+Physics.%0aAn+optical+resonator+system+is+analogous+to+an+electronic+resonant+circuit+but+uses+photons+instead+of+electrons.+Resonators+come+in+different+shapes%2c+but+they+all+involve+reflective+material+that+captures+light+for+a+period+of+time+as+it+bounces+back+and+forth+between+or+around+its+surface.+These+components+are+found+in+anything+from+lasers+to+high+precision+measuring+devices.%0aFor+their+research%2c+Yang%26rsquo%3bs+team+used+a+type+of+resonator+known+as+a+whispering+gallery+mode+resonator+(WGMR).+It+operates+in+a+manner+similar+to+the+whispering+gallery+at+St.+Paul%26rsquo%3bs+Cathedral%2c+where+a+person+on+one+side+of+the+room+can+hear+a+person+whispering+on+the+other+side.+What+the+cathedral+does+with+sound%2c+however%2c+WGMRs+do+with+light+%26mdash%3b+trapping+light+as+it+reflects+and+bounces+along+the+curved+perimeter.%0aIn+an+idealized+system%2c+a+fiber+optic+line+intersects+with+a+resonator%2c+a+ring+made+of+silica%2c+at+a+tangent.+When+a+photon+in+the+line+meets+the+resonator%2c+it+swoops+in%2c+reflecting+and+propagating+along+the+ring%2c+exiting+into+the+fiber+in+the+same+direction+it+was+initially+headed.%0aReality%2c+however%2c+is+rarely+so+neat.%0a%26ldquo%3bFabrication+in+high+quality+resonators+is+not+perfect%2c%26rdquo%3b+Yang+said.+%26ldquo%3bThere+is+always+some+defect%2c+or+dust%2c+that+scatters+the+light.%26rdquo%3b+What+actually+happens+is+some+of+the+scattered+light+changes+direction%2c+leaving+the+resonator+and+traveling+back+in+the+direction+whence+it+came.+The+scattering+effects+disperse+the+light%2c+and+it+doesn%26rsquo%3bt+exit+the+system.%0aImagine+a+box+around+the+system%3a+If+the+light+entered+the+box+from+the+left%2c+then+exited+out+the+right+side%2c+the+box+would+appear+transparent.+But+if+the+light+that+entered+was+scattered+and+didn%26rsquo%3bt+make+it+out%2c+the+box+would+seem+opaque.%0aBecause+manufacturing+imperfections+in+resonators+are+inconsistent+and+unpredictable%2c+so+too+was+transparency.+Light+that+enters+such+systems+scatters+and+ultimately+loses+its+strength%3b+it+is+absorbed+into+the+resonator%2c+rendering+the+system+opaque.%0aIn+the+system+devised+by+co-first+authors+Changqing+Wang%2c+a+PhD+candidate%2c+and+Xuefeng+Jiang%2c+a+researcher+in+Yang%26rsquo%3bs+lab%2c+there+are+two+WGMRs+indirectly+coupled+by+a+fiber+optic+line.+The+first+resonator+is+higher+in+quality%2c+having+just+one+imperfection.+Wang+added+a+tiny+pointed+material+that+acts+like+a+nanoparticle+to+the+high-quality+resonator.+By+moving+the+makeshift+particle%2c+Wang+was+able+to+%26ldquo%3btune%26rdquo%3b+it%2c+controlling+the+way+the+light+inside+scatters.%0aImportantly%2c+he+was+also+able+to+tune+the+resonator+to+what%26rsquo%3bs+known+as+an+%26ldquo%3bexceptional+point%2c%26rdquo%3b+a+point+at+which+one+and+only+one+state+can+exist.+In+this+case%2c+the+state+is+the+direction+of+light+in+the+resonator%3a+clockwise+or+counterclockwise.%0aFor+the+experiment%2c+researchers+directed+light+toward+a+pair+of+indirectly+coupled+resonators+from+the+left+(see+illustration).+The+lightwave+entered+the+first+resonator%2c+which+was+%26ldquo%3btuned%26rdquo%3b+to+ensure+light+traveled+clockwise.+The+light+bounced+around+the+perimeter%2c+then+exited%2c+continuing+along+the+fiber+to+the+second%2c+lower-quality+resonator.%26nbsp%3b%0aThere%2c+the+light+was+scattered+by+the+resonator%26rsquo%3bs+imperfections+and+some+of+it+began+traveling+counter-clockwise+along+the+perimeter.+The+light+wave+then+returned+to+the+fiber%2c+but+headed+back+toward+the+first+resonator.%0aCritically%2c+researchers+not+only+used+the+nanoparticle+in+the+first+resonator+to+make+the+lightwaves+move+clockwise%2c+they+also+tuned+it+in+a+way+that%2c+as+the+light+waves+propagated+back+and+forth+between+resonators%2c+a+special+interference+pattern+would+form.+As+a+result+of+that+pattern%2c+the+light+in+the+resonators+was+canceled+out%2c+so+to+speak%2c+allowing+the+light+traveling+along+the+fiber+to+eek+by%2c+rendering+the+system+transparent.%26nbsp%3b%0aIt+would+be+as+if+someone+shined+a+light+on+a+brick+wall+%26mdash%3b+no+light+would+get+through.+But+then+another+person+with+another+flashlight+shined+it+in+the+same+spot+and%2c+all+of+a+sudden%2c+that+spot+in+the+wall+became+transparent.%0aOne+of+the+more+important+%26mdash%3b+and+interesting+%26mdash%3b+functions+of+EIT+is+its+ability+to+create+%26ldquo%3bslow+light.%26rdquo%3b+The+speed+of+light+is+always+constant%2c+but+the+actual+value+of+that+speed+can+change+based+on+the+properties+of+the+medium+through+which+it+moves.+In+a+vacuum%2c+light+always+travels+at+300%2c000%2c000+meters+per+second.%0aWith+EIT%2c+people+have+slowed+light+down+to+eight+meters+per+second%2c+Wang+said.+%26ldquo%3bThat+can+have+significant+influence+on+the+storage+of+light+information.+If+light+is+slowed+down%2c+we+have+enough+time+to+use+the+encoded+information+for+optical+quantum+computing+or+optical+communication.%26rdquo%3b+If+engineers+can+better+control+EIT%2c+they+can+more+reliably+depend+on+slow+light+for+these+applications.%0aManipulating+EIT+could+also+be+used+in+the+development+of+long+distance+communication.+A+tuning+resonator+can+be+indirectly+coupled+to+another+resonator+kilometers+away+along+the+same+fiber+optic+cable.+%26ldquo%3bYou+could+change+the+transmitted+light+down+the+line%2c%26rdquo%3b+Yang+said.%0aThis+could+be+critical+for%2c+among+other+things%2c+quantum+encryption.%0aReference%3a+%26ldquo%3bElectromagnetically+induced+transparency+at+a+chiral+exceptional+point%26rdquo%3b+by+Changqing+Wang%2c+Xuefeng+Jiang%2c+Guangming+Zhao%2c+Mengzhen+Zhang%2c+Chia+Wei+Hsu%2c+Bo+Peng%2c+A.+Douglas+Stone%2c+Liang+Jiang+and+Lan+Yang%2c+13+January+2020%2c+Nature+Physics.%0aDOI%3a+10.1038%2fs41567-019-0746-7%0aThe+research+team+also+included+collaborators+at+Yale+University%2c+University+of+Chicago+and+the+University+of+Southern+California.

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