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SQUID

SQUID. Guido Torrioli Institute for Photonics and Nanotechnologies IFN – CNR Rome. Introduction. Supercontucting QUantum Interference Device SQUID. Magnetic Flux. SQUID. Voltage. Transducer. Extreme sensitivity , close to the quantum limit.

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SQUID

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  1. SQUID Guido Torrioli Institute for Photonics and Nanotechnologies IFN – CNR Rome

  2. Introduction SupercontuctingQUantumInterferenceDeviceSQUID Magnetic Flux SQUID Voltage • Transducer • Extremesensitivity, closeto the quantum limit • Measuresmagneticflux and any other physical quantity • that can be converted into magnetic flux

  3. Introduction Superconductingloop + Josephsonjunctions Josephson junctions Josephson junction rf-SQUID dc-SQUID rfbiasmagneticallycoupledto the SQUID dccurrentbias

  4. Basicphenomena Superconductivity • Cooper pairs • Zero resistance • Low Temperature Superconductors (LTSs) • High Temperature Superconductors (HTSs) Fluxquantization • MagneticFlux threading a superconductingloopisquantized where Tunnel Josephsoneffect • Tunnelingof Cooper pairsthrough • a thininsulatingbarrier (weak link) • Criticalcurrent

  5. Briefhistory • 1911Kamerlingh-Onnesdiscoverdsuperconductivity • 1957Bardeen–Cooper–Schrieffertheory • 1962Josephsoneffect • 1964 First dc-SQUID(R. Jaklevic, J. J. Lambe, J. Mercereau, A. Silver) • 1965 First rf-SQUID(R. Jaklevic, J. J. Lambe, A. Silver, J. E. Zimmerman)

  6. rf-SQUID rf-SQUID • Single JosephsonJunction • Radio frequencybiasinductivelycoupledto the SQUID loop • Largernoisecomparedto the dc-SQUID • Standard device in the 1970s and 1980s

  7. rf-SQUID rf-SQUIDasqubit Chiarello’s talk on superconductingqubits

  8. dc-SQUIDworkingprinciples

  9. dc-SQUIDworkingprinciples “OneFlux quantum isabout the fluxofearth’s magneticfield through a single human redbloodcell” (John Clarke)

  10. Dc-SQUID layout Thin-filmcouplingscheme(Ketchen and Jaycox)

  11. Energy sensitivity Coupledenergysensitivity Coupledenergysensitivity P. Carelli et al; Appl. Phys. Lett. 72, 115 (1998); doi: http://dx.doi.org/10.1063/1.121444

  12. SQUID readout Main problems: • Very small voltage across the SQUID: Vpp 10...50mV • Transfer coefficient VF = dV/dF depends on SQUID working point • Very small linear flux range: Flin << F0 Main tasks of a SQUID readout electronics: • Linearizetransfer function to provide a larger dynamic range • Amplify the weak SQUID voltage without adding noise dc SQUID Readout Small change in applied flux dFa results in small change in SQUID voltage dV

  13. Readoutelectronics FLL FluxLockedLoop Feedback flux counterbalances applied flux • Output voltage Vf depends linearly on applied flux • Very large dynamic range possible • Transfer function does no longer depend on SQUID working point

  14. SQUID readout – FluxModulation • FluxModulationReadout • A modulationfluxisappliedto the SQUID • Useof a cold transformer • The appliedfluxissensedbysincrhonouslydetecting the SQUID voltage • at the modulationfrequency (Lock-in) • Mainrestrictions • Limited FLL bandwidth • ReducedSlew-Rate • Complicatedelectronics

  15. SQUID Readout – Direct • Additional Positive Feedback • APF circuitmakes the V-Fcharacteristicstronglyasymetric • The voltage transfer coefficientisboostedat the workingpoint D Drunget at, Appl. Phys. Lett. 57 406-408 (1990).

  16. SQUID Readoutotherconfiguration • Two stage SQUID • Largevoltage transfer coefficient • Problem: multiple workingpoint • SQUID Array • SQUIDs are connected in series • FluxisalppliedtoallSQUIDsthrough input coils • connected in series • Voltage output isaddedcostructively • LargeVoltage swing

  17. SQUID Applications SQUID measures any quantity convertible into magnetic flux • Magnetic field: • Biomagnetism • Non-destructive evaluation (NDE), • Nuclear magnetic resonance (NMR, MRI), • SQUID microscopes, • geophysics • Electric current: • Cryogenic radiation and particle detectors (TES etc), • Cryogenic current comparators (CCCs) for metrological applications • Mechanical displacement: • Gravitational wave detection

  18. TES readout • TransitionEdgeSensor • TESs are cryogenicenergysensorsuitabletodetect • radiationfrommillimeter-wave to γ-ray • NEP can be in the order of 10-19 W/√Hz • Squidreadoutisneeded in ordertoreachsuch a low NEP • Standard single TES readout • TES isvoltagebiased • ElectroThermal Feedback (ETF) (negative) • SQUID readout (sensitivity, working temperature)

  19. SQUID Multiplexing • ApplicationswithlargemosaicarrayofTESs • Problemwithheatload and complexityof the cryo-harness • Multiplexing • Signals are combined at low temperature and thenseparated • at room temperature • Twomain multiplexing schemes • TimeDivision Multiplexing (TDM) • FrequencyDivision Multiplexing (FDM)

  20. TDM Multiplexing TimeDivision SQUID Multiplexing (developedat NIST) • TESs are dcbiased • SQUIDs are turned on and off sequentiallyforeachrow • DrawbackManySQUIDs

  21. FDM multiplexing FrequencyDivision SQUID Multiplexing • TESs are AC biased (samefrequencyforeveryraw) • One SQUID readsonecolumn • DrawbackVerydemanding performance forFLL SQUID dinamycs

  22. Microstrip SQUID Amplifier PushingtowardHigherFrequencies • SQUID applicationswith the FLL scheme are operating in the frequencyrange • from DC tofew MHz • Operating the SQUID in “open-loop” mode, wouldincrease the high frequency cut-off • At frequencies above 100–200 MHz, however, parasitic capacitance between the washer • and input coil drastically reduces the gain . • This problem can be overcome by operating the coil and washer as a microstrip resonator Conventional SQUID Amplifier Microstrip SQUID Amplifier • Signal connected to both ends of coil • Signal connected to one end of the coil and SQUID washer • The other end of the coil is left open Michael Mück, Christian Welzel, and John Clarke, AppliedPhysicsLetters 82, 3266 (2003); doi: 10.1063/1.1572970

  23. Microstrip SQUID Amplifier Microstrip SQUID Amplifier • With Microstrip SQUID Amplifier, frequency detection ispushed up toGHzrange • Thissolutionhasbeenadopted in the “Axion Dark MatterExperiment (ADMX) “

  24. Conclusions Conclusions • SQUID measures any quantity convertible into magnetic flux • At low temperatures, the resolution of SQUID amplifiers is • essentially limited by Heisenberg’s Uncertainty Principle • SQUIDs are remarkably broadband: from DC to 109 Hz • SQUIDs may make contribution to the search for axions, • both in the TES reading and in the direct detection of microwave photons

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