The Original SQUID

The Original SQUID

Arnold H. Silver

Josephson Symposium

Applied Superconductivity Conference

Portland, OR

October 9, 2012

Two Part Presentation

• Phase One: 1963 – 1964 Jaklevic, Lambe, Mercereau, Silver

– Microwave observations by John Lambe

– Thin film interferometers

– First two-Josephson tunnel junction macroscopic quantum interference

– Quantum wave phase shifts

– Other tunnel junction macroscopic quantum interference experiments

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• Phase Two: 1964 – 1968 Silver and Zimmerman– Point contacts

– Bulk Nb SQUIDs

– dc, rf, and R SQUIDs

– Flux-quantum based SQUID model

– Linearized SQUID magnetometer

– Measured SQUID flux-quantum states

ASC 2012, Portland, OR Arnold Silver

2

Ford Scientific Lab

Lambe, Zimmerman, Silver, Jaklevic, Mercereau


We Used 1960’s Technology

• Analog electronics– Vacuum-tubes

– Oscilloscopes

– X-Y recorders

• Glass, double-jacket LHe dewars

• Manuscripts– Typewritten

– Literally “cut and paste”

– Hand-plotting on graph paper

– Trace on vellum for publication

• 3” x 4” glass slides

3 ASC 2012, Portland, OR Arnold Silver


Phase One: 1963 – 1964Jaklevic, Lambe, Mercereau, Silver

• Microwave observations by John Lambe

• First 2-Josephson tunnel junction

macroscopic quantum interference

• Vector potential measurement

• Quantum wave phase shifts

• Other tunnel junction macroscopic quantum

interference experiments

5

Periodic Microwave Signals (1963)

15 microgauss periodicity

Submitted to Physics

Letters in June 1964


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First 2-Josephson-Junction

Macroscopic Quantum Interferometer

Tin thin-film macroscopic quantum interferometer with

two Josephson tunnel junctions (1) and (2)

• Microscope slide substrates

• Stainless steel shim masks

• Formvar insulating aperture “A”

• Sn thin films


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Measuring Josephson Tunnel Junction IC

� Oscilloscope trace

� Hysteretic I-V characteristic

� Requires current cycling

� Automated measurement

� Sinusoidal current source

� Synchronous detector voltage linear in

critical current


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Small solenoid

inserted here


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We Did Other Tunnel Junction

Experiments

• Measured Josephson junction “kinetic” inductance, LJ, vs I/IC at 30 MHz using an RCA rf voltmeter.

• Measured deBroglie wavelength of supercurrent in a

film thinner than the London-penetration-length which

generates phase shifts along the film detected by

Josephson junctions.



Phase Two: 1964 – 1968

Silver and Zimmerman

• Point contact junctions

• Bulk Nb SQUIDs

• dc, rf, and R SQUIDs

• Flux-quantum based SQUID model

• Linearized SQUID magnetometer

• Measured SQUID flux-quantum states

ASC 2012, Portland, OR Arnold Silver12

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“Junction” Comparisons

V (µµµµV)

• Josephson tunnel junctionHysteretic

• Millivolt signals

Required current cycling

• Point-contact “weak-link”• Single valued

• Microvolt signals


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Point Contact SQUIDs in Bulk Niobium

• SQUIDs were machined from bulk Nb

• Pointed 000-120 Nb screws

• Screws were adjustable in LHe with long wrench, nut, and

locking washer


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Single Junction RF SQUID


ASC 2012, Portland, OR Arnold Silver16

ΦΦΦΦ0 ΦΦΦΦ0

RF Current

RF Voltage

RF SQUID Response

• Periodic in RF amplitude and

magnetic field

• Similar to early microwave

observations

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RF SQUID Oscilloscope Video


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RF SQUID Diagnostics


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SQUID Quantized Flux States and Transitions

β =2πLI

C

Φ0

Single valued for

Multiple-valued for

For there is an

inflection point where

φ φ φ φ = φφφφex = ΦΦΦΦ0/2 and I = 0.

β ≤1

β >1

β ≤1


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RF SQUID Flux Quantum States Measured With Linearized RF SQUID Magnetometer


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SQUID Quantized States and Transitions

Theory Measurement


β >1

β <1

Resistive R-SQUID VCO

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• Micro-ohm resistance

• X-band, 10 GHz, cavity

• Josephson ac effect

V = Φ0f


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How We Did It!

• Good Luck

• Inquisitiveness

• Serendipity

• Persistence

• Free from programmatic constraints


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First Magnetocardiogram MCG@ MIT Magnet Lab

Zimmerman, Cohen, Edelsack


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SQUID Evolution SummaryFord Motor Company Scientific Laboratory

1963 1964 1965 1966 1967 1968


The Original SQUID

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Transcript of The Original SQUID