Superconducting quantum interference devices : an ...

1 FUrn*J<i*S:I IAt*\-'H- > :anOperationalGuideforrf-BiasedSystemsNA TIONALBUREAUOFSTANDARDSTheNationalBureau ofStandards1wasestablishedbyanactofCongr essMarch3, 'soverallgoalistostrengthenandadvancethe Nation' ,theBureauconductsresearchandprovides:(1 )abasisfortheNation'sphysicalmeasure-men tsystem,(2)scientificandtechnologicalser vicesforindustryandgovernment,(3)atechni calbasisforequityintrade,and(4) ,theInstituteforMaterialsResearch,theIns tituteforAppliedTechnology,theCenterforC omputerSciencesandTechnology, ;coordinatesthatsystemwithmeasurementsys temsofothernations.

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5 *PartnfHipPentprforRnildinp-TerhnolncvJA N24 ISPSS uperconductingQuantumInterferenceDevices :\ anOperationalGuideforrf-BiasedSystemsV3 e> ,Colorado80302 NBST echnicalNotesaredesignedtosupplementtheB ureau' *. , ,SecretaryNATIONALBUREAUOFSTANDARDS, , ( ), ,47pages(November1972)CODEN:NBTNAEF orsalebyiheSuperintendentofDocuments, ,Washington, ( :629). 18inFigures(continued) ( Superconducting ) (SQUID's).Inthecourseofroutineoperationo fthesedevicesoneamassesasetofoperational rules, :thereadoutcir-cuitry,operationallimitso ftheSQUID,rf-couplingtotheSQUID,fluxtran sformers, :Electricalmeasurements;quantuminterfer^ encedevices; (SQUID's).

6 'sintentiontodwellonanumberofthepractica laspectsfromthislattercategorywhichwill, hopefully, [1,2].TheSQUID alsohasamechanicalanalogwhichcanbehelpfu lindevelopingsomeinsightintoitsoperating characteristics[3]. , ; , , ,theresonantcircuitcoupledtoit, , , , ,theSQUID isasmallsuperconductinginductanceconnect edinserieswithoneofafewtypesofweakJoseph son[4] ^ ,thecoilcoupledtotheSQUID,acoaxialtransm is-sionline, 'frontend' ,X/4 , , ,inducedbyalteringthefluxlinkingtheSQUID , , (byvaryingthecouplingcapacitor).Atsomeci riticalrfcurrentvalue, ,thisperiodicresponsedisappearsandthenre appearsatayethigherlevelwithareversalinp hase(oranoffsetofcp/2).

7 ,infact, (theresponseoutlinedabovehasbeenoptimize dbyadjustmentofinputcircuitparameters). (thelowfrequencycurrentispassedthroughth erfcoiltogeneratethislowfrequencyfieldat theSQUID). (PSD).Withthecircuitarrangedasshowninfig ure3,andthemodulationleveladjustedto19pe ak-to-peak,thephasesensitivedetector(sen singthefundamentaloscillation) (withtf'U <uHdOo-t->+-> 382>Oa,0) 3Od, ds ia rtcoT3<U *asa4 Jrd<u. = $cuo <uft,dd*8p^LJ-t->Ow(Jcurtdo>ftcuCO,-Hcu s,IDaCOcurdGuOd:>>>oJ^CUftftcuaidooUCUCU *wcuCJcuCOcurdcurdenCMcu+*.)

8 S? h3dcuCOCU*H<UT3* >cud^cuperiodicutpitin f* (PSD) ,anexternalfluxap-pliedtotheSQUID willresultinadcfeedbackcurrent(throughth erfcoilcoupledtotheSQUID) ( ).However,thiscircuitprovidescontinuousd isplayoftheresponseatdifferentrfcurrentl evelsandisconvenientforSQUID adjustment( ).ThePSD(phasesensi-tivedetector) )thenthesystemwilllockontoapeak(orvalley ) ,asanexternalfieldisappliedtotheSQUID, ,showninthefigure, ,Webb,andWheatley[5].Beforeproceedingtot henextsection, , (9/2) ,amodulator(fortheinternalrfoscillator) ' >S|gQ c<jXI<uaoXUrg <4 HOCJftCOomP"-HIT)CDW) i-io(U^3T)CD4 JnJJh0)a<uCOtiU<va< >oCDaIDaw<u**^dabo l-< !

9 -!.-H< 's, (whichisnotingeneralusenow)isthesingle-hole, 'sdevelopedbySilverandZimmerman[6] 1/2>SiL(i)=y-(t) < (3< ,theimped-ancereflectedintothetankcircuitisprimarilyreactiveandcausesashiftinitsresonantfrequency(thisaccountsforthefailuretoseemuch11 .A\V\\\AXVA\\\\\\v\\\\\\\\\\CO<=>niCOdT>PdCOrHrrt-t->j->a^- ->OCO i-iT36 rHPh1) rHH->8rHMCC)o rHrH0)rdrH0)COCOdrHaCJCO rHnQi io i-HddIDa(LICJ1 COCOi-HCOaCOd<+HO rH i-inCOU iH0)43 Ootut)X!CO^-i->COoda! 1-1acrtCO4->>rHOT)orHcti+->d(1)d rHaoordCOui i<1> t-<dCOrH<+Hd HoCOo rHPh<+HmOpr-lCOCOCOdPi iIDaHrn\PCOaCOUlCO1 1 COHHo[-)COrdQi )aCO1 1ord rHH->rHdaCOodCOrH CO<+Hrdrdu-pCO+J<+HvirdCOCOCOrdHrH rH1 COo PhH->COrdCOcoPhH->dCOah->Ha;H->uCOuCOCO rHi 14->COd r-i rHrHT)P-t->CCJ(1)ccj!]

10 HH->cciCOdodrdCOa<H->dCOdHr 1oabflaCOrH rHdCOLhCOoft12effectwhentheoscillatoriss etatthetunedcircuit'sresonantfrequency). For> <10,thedampingofthepointcontactjunctiona llowsonlyasinglequantumoffluxtomoveinand outoftheringduringeachcycle(assumingther fbiascurrentissetatthelowestperiodicpatt ern).For0^10, [7]typeofSQUID[8] ,however, , , ,therangeofoperationofthistypeofSQUID isgreaterthanforpointcontactdevices, ,etal.[2] (andthisisdoneatroomtemperature) ,itdoesnotrespondtoauniformfield, (10-15turns)iscoupledintooneofthetwohole sjustasisdonewiththesingleholeSQUID andadccoilorfluxtransformercoilis13plugg edintothesecondhole(seesectionVI) [9] ,towhichthedevicecouples, (forinstance,byaconcentriccoil).