Quantum information science is a new field of science and technology which requires the collaboration of researchers coming from different fields of physics, mathematics, and engineering: both theoretical and applied. Quantum Computing and Quantum Bits in Mesoscopic Systems addresses fundamental aspects of quantum physics, enhancing the connection between the quantum behavior of macroscopic systems and information theory. In addition to theoretical quantum physics, the book comprehensively explores practical implementation of quantum computing and information processing devices. On the experimental side, this book reports on recent and previous observations of quantum behavior in several physical systems, coherently coupled Bose-Einstein condensates, quantum dots, superconducting quantum interference devices, Cooper pair boxes, and electron pumps in the context of the Josephson effect. In these systems, the book discusses all required steps, from fabrication through characterization to the final basic implementation for quantum computing.

Thisvolumereportsthemajorpartofthescientificcontributionsofthefirstinternational workshoponSuperconductingNano-ElectronicsDevices(SNED)heldinNapoli,Italy,at theendofMay2001. Theaimoftheworkshopwastofocusonrecentexperimentalandtheoreticalresultsin thefieldofsuperconductingnano-electronicsdevices. Itcombinedphysicswithpresent andfuturetechnologicalapplications:bothfundamentalandappliedaspectswerecovered. SpecialemphasiswasgiventoquantumcoherenceandcomputationusingsmallJosephson junctions,noiseinultrasensitivenanodevicesandpossibilitiesofmakinguseofsupercon- ductivityinvariouson-chipdevices. Withtheseattributesandwithrecognizedinvited speakersintheirspecialtiestheworkshopmanagedtobringtogetheracollectionof scientistsfromnearbybutdistinctresearchcommunities. Thiswaytheatmosphereofthe workshopbecameveryopenanddiscussionswerelivelybothduringandoutsidethe sessions. Thisfreshdiscussionhopefullygaveeveryparticipantalotofnewideasfor furtherworkbackintheirhomeinstitutes. OneofthecentraltopicsintheworkshopwastheuseofdifferentJosephsonjunction configurationsasimplementationsofquantumbits. Atthetimeoftheworkshopwewere justwaitingforthesecondwaveofbreakthroughsinthisfield:theresultsemergingfrom theparticipatinglaboratoriesoftheworkshopjustatthetimeofthewritingofthispreface perhapsalsoprovetheusefulnessofourworkshop. Anotherfocuswasonvarioustopicsrelatedtoultrasensativedetectors. Theybring quantumlimitationstoapplications,andmanydeviceconceptsareresultsofunderstanding fundamentalandexcitingphenomenainsuperconductivity. Noiseandon-chipcooling wereexplicitlydiscussedinthedetectorsessionsaswell. ThechoiceofthelocationrecognizestheroleandthetraditionsofNapoliespeciallyin thefieldofmacroscopicquantumcoherence,oneofthemainissuesoftheworkshop. It furtherguaranteedtheparticipantsastimulatingatmosphereatthemeeting. Inconclusion,wewishtothanktheIstitutoItalianopergliStudiFilosofici,theIstituto diCiberneticadelConsiglioNazionaledelleRicerche,theUniversityofJyviiskylii,the IstitutoNazionalediFisicaNucleare,theIstitutoNazionalediFisicadellaMateria,the DipartimentoScienzeFisiche,andtheRettoratodell'UniversitadiNapoli"FedericoII" fortheirsupport. ThanksarealsoduetoAirLiquide,CRY,Nanoway,OxfordInstruments, andRaith. ThisinitiativeisintheframeoftheinternationalactivityofMQC2Association on"MacroscopicQuantumCoherenceandComputing. "WeareindebtedtoC. Granata v vi PREFACE and V. Coratoforscientificassistance,andtoF. Caiazzo,E. DeGrazia,andA. M. Mazzarellafortheirvaluableassistanceinallthetasksconnectedtotheorganizationofthe Workshop. WearealsogratefultoL. Longobardi,A. Monaco,S. Piscitelli,andS. Rombetto forhintsandhelpduringtheWorkshop. ThanksareduetoL. DeFelice,S. Luongo,and V. Sindonifortheorganizationofthesocialevent. J. Pekola B. Ruggiero P. Silvestrini CONTENTS QuantumNondemolitionMeasurementsofaQubit . D. V. Averin BayesianQuantumMeasurementofaSingle-Cooper-PairQubit 11 A. Korotkov lIfNoiseinJosephsonQubits 15 E. Paladino, L. Faoro,G. Falci,and R. Fazio SwitchingCurrentsandQuasi-ParticlePoisoningintheSuperconducting SingleElectronTransistor 25 P. Agren,J. Walter,V. Sch611mann,andD. B. Haviland JosephsonSystemsforQuantumCoherenceExperiments 33 V. Corato,C. Granata, L. Longobardi,M. Russo,B. Ruggiero, andP. Silvestrini SolidStateAnalogueofDoubleSlitInterferometer...43 K. Yu. Arutyunov, T. T. Hongisto,andJ. P. Pekola NoiseandMicrowavePropertiesofSET-Transistors...53 M. Ejrnres,M. T. Savolainen,andJ. Mygind UseofSmallThnnelJunctionsOperatingatT=0. 3K 63 R. Leoni,M. G. Castellano,F. Chiarello,andG. Torrioli AHystericSingleCooperPairTransistorforSingleShotReadingof 73 aCharge-Qubit A. Cottet,D. Vion,P. Joyez,D. Esteve,andM. H. Devoret SingleCooperPairElectrometerBasedonaRadio-Frequency-SQUID Scheme 87 A. B. Zorin vii viii CONTENTS PossibilityofSingle-ElectronDevicesandSuperconductingCoherence 97 Yu. A. Pashkin, Y. Nakamura,T. Yamamoto,andJ. S. Tsai Frequency-LockedCurrentofCooperPairsinSuperconductingSingle ElectronTransistorwithOhmicResistor...105 S. V. Lotkhov,S. A. Bogoslovsky, A. B. Zorin,andJ. Niemeyer SetupforExperimentsontheSupercurrent-PhaseRelationinBloch Transistors-StatusandPossibleApplications 115 M. Gotz, V. V. Khanin, A. B. Zorin,E. Il'ichev,S. A. Bogoslovsky, andJ. Niemeyer Single-ElectronTransistorsintheRegimeofHighConductance...123 C. Wallisser,B;Limblach,P. yomStein,and R. Schiifer SuperconductingTransistor-EdgeSensorsforTime&EnergyResolved Single-PhotonCountersandforDarkMatterSearches 133 B. Cabrera OptimizationoftheHot-ElectronBolometerandaCascadeQuasiparticle 145 L. Kuzrnin NoiseinRefrigeratingTunnelJunctionsandinMicrobolometers...153 D. V. Anghel NonequilibriumQuasiparticlesandElectronCoolingbyNormalMetal- SuperconductorTunnelJunctions...165 D. Golubevand A. Vasenko MesoscopicJosephsonJunctionsCoupledtoWeakCoherentFields: AnExampleofReciprocalDetection 175 R. Miglioreand A. Messina DynamicsofSuperconductingInterferometersContainingPi-Junctions 183 V. K. Kornev, I. I. Soloviev, I. V. Borisenko,P. B. Mozhaev, andG. A.

This volume is an outgrowth of the Second International Workshop on Macroscopic Quantum Coherence and Computing held in Napoli, Italy, in June 2000. This workshop gathered a number of experts from the major Universities and Research Institutions of several countries. The choice of the location, which recognizes the role and the traditions of Naples in this field, guaranteed the participants a stimulating atmosphere. The aim of the workshop has been to report on the recent theoretical and experimental results on the macroscopic quantum coherence of macroscopic systems. Particular attention was devoted to Josephson devices. The correlation with other atomic and molecular systems, exhibiting a macroscopic quantum behaviour, was also discussed. The seminars provided both historical overview and recent theoretical ground on the topic, as well as information on new experimental results relative to the quantum computing area. The first workshop on this topic, held in Napoli in 1998, has been ennobled by important reports on observations of Macroscopic Quantum Coherence in mesoscopic systems. The current workshop proposed, among many stimulating results, the first observations of Macroscopic Quantum Coherence between macroscopically distinct fluxoid states in rf SQUIDs, 20 years after the Leggett's proposal to experimentally test the quantum behavior of macroscopic systems. Reports on observations of quantum behaviour in molecular and magnetic systems, small Josephson devices, quantum dots have also been particularly stimulating in view of the realization of several possible q-bits.

Quantum information science is a new field of science and technology which requires the collaboration of researchers coming from different fields of physics, mathematics, and engineering: both theoretical and applied. Quantum Computing and Quantum Bits in Mesoscopic Systems addresses fundamental aspects of quantum physics, enhancing the connection between the quantum behavior of macroscopic systems and information theory. In addition to theoretical quantum physics, the book comprehensively explores practical implementation of quantum computing and information processing devices.
On the experimental side, this book reports on recent and previous observations of quantum behavior in several physical systems, coherently coupled Bose-Einstein condensates, quantum dots, superconducting quantum interference devices, Cooper pair boxes, and electron pumps in the context of the Josephson effect. In these systems, the book discusses all required steps, from fabrication through characterization to the final basic implementation for quantum computing.

Thisvolumereportsthemajorpartofthescientificcontributionsofthefirstinternational workshoponSuperconductingNano-ElectronicsDevices(SNED)heldinNapoli,Italy,at theendofMay2001. Theaimoftheworkshopwastofocusonrecentexperimentalandtheoreticalresultsin thefieldofsuperconductingnano-electronicsdevices. Itcombinedphysicswithpresent andfuturetechnologicalapplications:bothfundamentalandappliedaspectswerecovered. SpecialemphasiswasgiventoquantumcoherenceandcomputationusingsmallJosephson junctions,noiseinultrasensitivenanodevicesandpossibilitiesofmakinguseofsupercon- ductivityinvariouson-chipdevices. Withtheseattributesandwithrecognizedinvited speakersintheirspecialtiestheworkshopmanagedtobringtogetheracollectionof scientistsfromnearbybutdistinctresearchcommunities. Thiswaytheatmosphereofthe workshopbecameveryopenanddiscussionswerelivelybothduringandoutsidethe sessions. Thisfreshdiscussionhopefullygaveeveryparticipantalotofnewideasfor furtherworkbackintheirhomeinstitutes. OneofthecentraltopicsintheworkshopwastheuseofdifferentJosephsonjunction configurationsasimplementationsofquantumbits. Atthetimeoftheworkshopwewere justwaitingforthesecondwaveofbreakthroughsinthisfield:theresultsemergingfrom theparticipatinglaboratoriesoftheworkshopjustatthetimeofthewritingofthispreface perhapsalsoprovetheusefulnessofourworkshop. Anotherfocuswasonvarioustopicsrelatedtoultrasensativedetectors. Theybring quantumlimitationstoapplications,andmanydeviceconceptsareresultsofunderstanding fundamentalandexcitingphenomenainsuperconductivity. Noiseandon-chipcooling wereexplicitlydiscussedinthedetectorsessionsaswell. ThechoiceofthelocationrecognizestheroleandthetraditionsofNapoliespeciallyin thefieldofmacroscopicquantumcoherence,oneofthemainissuesoftheworkshop. It furtherguaranteedtheparticipantsastimulatingatmosphereatthemeeting. Inconclusion,wewishtothanktheIstitutoItalianopergliStudiFilosofici,theIstituto diCiberneticadelConsiglioNazionaledelleRicerche,theUniversityofJyviiskylii,the IstitutoNazionalediFisicaNucleare,theIstitutoNazionalediFisicadellaMateria,the DipartimentoScienzeFisiche,andtheRettoratodell'UniversitadiNapoli"FedericoII" fortheirsupport. ThanksarealsoduetoAirLiquide,CRY,Nanoway,OxfordInstruments, andRaith. ThisinitiativeisintheframeoftheinternationalactivityofMQC2Association on"MacroscopicQuantumCoherenceandComputing. "WeareindebtedtoC. Granata v vi PREFACE and V. Coratoforscientificassistance,andtoF. Caiazzo,E. DeGrazia,andA. M. Mazzarellafortheirvaluableassistanceinallthetasksconnectedtotheorganizationofthe Workshop. WearealsogratefultoL. Longobardi,A. Monaco,S. Piscitelli,andS. Rombetto forhintsandhelpduringtheWorkshop. ThanksareduetoL. DeFelice,S. Luongo,and V. Sindonifortheorganizationofthesocialevent. J. Pekola B. Ruggiero P. Silvestrini CONTENTS QuantumNondemolitionMeasurementsofaQubit . D. V. Averin BayesianQuantumMeasurementofaSingle-Cooper-PairQubit 11 A. Korotkov lIfNoiseinJosephsonQubits 15 E. Paladino, L. Faoro,G. Falci,and R. Fazio SwitchingCurrentsandQuasi-ParticlePoisoningintheSuperconducting SingleElectronTransistor 25 P. Agren,J. Walter,V. Sch611mann,andD. B. Haviland JosephsonSystemsforQuantumCoherenceExperiments 33 V. Corato,C. Granata, L. Longobardi,M. Russo,B. Ruggiero, andP. Silvestrini SolidStateAnalogueofDoubleSlitInterferometer...43 K. Yu. Arutyunov, T. T. Hongisto,andJ. P. Pekola NoiseandMicrowavePropertiesofSET-Transistors...53 M. Ejrnres,M. T. Savolainen,andJ. Mygind UseofSmallThnnelJunctionsOperatingatT=0. 3K 63 R. Leoni,M. G. Castellano,F. Chiarello,andG. Torrioli AHystericSingleCooperPairTransistorforSingleShotReadingof 73 aCharge-Qubit A. Cottet,D. Vion,P. Joyez,D. Esteve,andM. H. Devoret SingleCooperPairElectrometerBasedonaRadio-Frequency-SQUID Scheme 87 A. B. Zorin vii viii CONTENTS PossibilityofSingle-ElectronDevicesandSuperconductingCoherence 97 Yu. A. Pashkin, Y. Nakamura,T. Yamamoto,andJ. S. Tsai Frequency-LockedCurrentofCooperPairsinSuperconductingSingle ElectronTransistorwithOhmicResistor...105 S. V. Lotkhov,S. A. Bogoslovsky, A. B. Zorin,andJ. Niemeyer SetupforExperimentsontheSupercurrent-PhaseRelationinBloch Transistors-StatusandPossibleApplications 115 M. Gotz, V. V. Khanin, A. B. Zorin,E. Il'ichev,S. A. Bogoslovsky, andJ. Niemeyer Single-ElectronTransistorsintheRegimeofHighConductance...123 C. Wallisser,B;Limblach,P. yomStein,and R. Schiifer SuperconductingTransistor-EdgeSensorsforTime&EnergyResolved Single-PhotonCountersandforDarkMatterSearches 133 B. Cabrera OptimizationoftheHot-ElectronBolometerandaCascadeQuasiparticle 145 L. Kuzrnin NoiseinRefrigeratingTunnelJunctionsandinMicrobolometers...153 D. V. Anghel NonequilibriumQuasiparticlesandElectronCoolingbyNormalMetal- SuperconductorTunnelJunctions...165 D. Golubevand A. Vasenko MesoscopicJosephsonJunctionsCoupledtoWeakCoherentFields: AnExampleofReciprocalDetection 175 R. Miglioreand A. Messina DynamicsofSuperconductingInterferometersContainingPi-Junctions 183 V. K. Kornev, I. I. Soloviev, I. V. Borisenko,P. B. Mozhaev, andG. A.

This volume is an outgrowth of the Second International Workshop on Macroscopic Quantum Coherence and Computing held in Napoli, Italy, in June 2000. This workshop gathered a number of experts from the major Universities and Research Institutions of several countries. The choice of the location, which recognizes the role and the traditions of Naples in this field, guaranteed the participants a stimulating atmosphere. The aim of the workshop has been to report on the recent theoretical and experimental results on the macroscopic quantum coherence of macroscopic systems. Particular attention was devoted to Josephson devices. The correlation with other atomic and molecular systems, exhibiting a macroscopic quantum behaviour, was also discussed. The seminars provided both historical overview and recent theoretical ground on the topic, as well as information on new experimental results relative to the quantum computing area. The first workshop on this topic, held in Napoli in 1998, has been ennobled by important reports on observations of Macroscopic Quantum Coherence in mesoscopic systems. The current workshop proposed, among many stimulating results, the first observations of Macroscopic Quantum Coherence between macroscopically distinct fluxoid states in rf SQUIDs, 20 years after the Leggett's proposal to experimentally test the quantum behavior of macroscopic systems. Reports on observations of quantum behaviour in molecular and magnetic systems, small Josephson devices, quantum dots have also been particularly stimulating in view of the realization of several possible q-bits.