SQUIDs Then and Now: From SLUGs to Axions · • Tangent magnetometer • Magnet and mirror...
Transcript of SQUIDs Then and Now: From SLUGs to Axions · • Tangent magnetometer • Magnet and mirror...
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SQUIDs Then and Now: From
SLUGs to Axions
Josephson 50th Anniversary
Applied Superconductivity Conference
Portland, OR
• SQUIDs Then
• SQUIDs Now
• Cold Dark Matter:
The Hunt for the Axion
9 October 2012
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SQUIDs Then…
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1 October 1964
• Royal Society Mond Laboratory
Cambridge University
• Thesis advisor: Brian Pippard
• Thesis research required measuring
voltages of 10−12 to10−13 volts
Eric Gill 1933
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• Tangent magnetometer
• Magnet and mirror suspended from a long
quartz fiber at the centre of a Helmholtz pair
• Current in the coil caused a deflection of a
reflected light beam
• Voltage resolution 1 pV in 12 s (≈ 3 pVHz-1/2)
A Superconducting GalvanometerA. B. Pippard and G. T. Pullan 1951
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Courtesy Brian Josephson
Brian Josephson Explains Tunneling
November 1964
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1961 to 1964
I
Superconductor 1 Superconductor 2
~ 20 Å
Insulatingbarrier
I
V
Φ = n Φ0
J
1961 1962
1963 1964 Φ
Φ
Φ0I0
Deaver and FairbankDoll and Näbauer
Josephson
Anderson and
Rowell
Jaklevic, Lambe, Silver and Mercereau
Φ0 ≡ h/2e
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Brian Pippard:
“John, How would you like a
voltmeter with a resolution of
2 × 10−15 V in 1 second?”
The Very Next Day—November 1964
Courtesy Kelvin Fagan
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Brian’s Idea
I
VoutVin
R
L L
M
M = L
τ = L/R
Digital voltmeter: IΦ0 = Φ0/M = Φ0/L
Voltage resolution: Vin = IΦ0R = Φ0/τ = 2 × 10-15 V
for τ = 1 s
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At Tea
• Paul Wraight pointed out that Nb has a surface oxide
layer and PbSn solder is a superconductor (February 1965)
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5 mm
At Tea
Copper
Niobium
SnPb
solder
I
I
V
• Paul Wraight pointed out that Nb has a surface oxide
layer and PbSn solder is a superconductor (February 1965)
Before dinner
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5 mm
Copper
Niobium
SnPb
solder
The Very Next Day
I
I
V
Brian Pippard:
It looks as though a slug
crawled through the
window last night and
expired on your desk!”
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5 mm
Copper
Niobium
SnPb
solder
The SLUG (Superconducting Low-Inductance Undulatory Galvanometer)
Current IB in niobium wire
Vo
ltag
e
February 1965
Nb wire
and solder
I
I
V
IB
IB
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5 mm
Copper
Niobium
Solder
The SLUG as a Voltmeter
Analog voltmeter
Voltage noise at 4.2 K
10 fVHz-1/2
(10-14 VHz-1/2)
V
1 µΩ
0 1 2Φo
Φ
δV
δΦ
V
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I(mA)
V(mV)
Vd(nV)
Vd
V
Observation of Charge Imbalance
• Current injected through the Al-AlOx-Sn
junction creates a charge imbalance between
the electron-like and hole-like quasiparticle
branches in the superconducting Sn film.
• This imbalance establishes a potential
difference across the Sn-SnOx-Cu junction.
• Detailed investigation of nonequilibrium
superconductivity.
(1)
(2)
(3)
(4)
SLUG
JC 1972
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Beasley and Webb 1967
0.001′′ Nb foil
0.001′′ mylar
0.03′′ Nb wire
Adjustable Niobium SQUID
Nb wire
and foil
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…and Now
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Thin-Film, Square Washer DC SQUID
SQUID with input coil
Josephson junctions
500 µµµµm 20 µµµµm
• Wafer scale process
• Photolithographic patterning
• Nb-AlOx-Nb Josephson junctions (John Rowell)
Ketchen and Jaycox (1981)
At 4.2 K
Flux noise: 1 – 2 µΦ0/Hz−1/2
~ Φ0/1,000,000 in 1 second
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Superconducting Flux Transformer:Magnetometer
SQUIDMagnetic field noise
~ 10-15 THz-1/2
B J
Closedsuperconducting
circuit
Roomtemperatureelectronics
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Magnetic Fields
1 femtotesla
tesla
10-16
10-10
10-8
10-6
10-4
10-12
10-14
10-2
1
Earth’s field
Urban noise
Car at 50 m
Human heart
Fetal heart
Human brain response
SQUID magnetometer
Conventional MRI
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Quantum Design "Evercool"
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UC Berkeley Flux Qubits
35 µµµµm
Qubit 1
Qubit 2
SQUID
UC Berkeley
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High-Tc SQUIDs Prospecting for Mineral Deposits
Courtesy Cathy Foley, CSIRO
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Gravity Probe-BTests of General Relativity
Courtesy Stanford University and NASA
• Geodetic effect—
curved space-time due
to the presence of the
Earth
• Lense-Thirring effect—
dragging of the local
space-time frame due to
rotation
• Gyroscopes:
Spinning, niobium-coated
sapphire sphere develops
magnetic dipole moment,
read out by a SQUID
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South Pole Telescope: Searching for galaxy clusters
• Antarctica 9,500 feet
• 960 transition edge sensors with
multiplexed SQUID readout
• 12,000 SQUIDs
The “Bullet Cluster”
UC Berkeley + Many other groups
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300-Channel SQUID Systems for Magnetoencephalography (MEG)
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Magnetic Resonance Imaging at 132 µµµµT
UC Berkeley
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Cold Dark Matter: The Hunt for the Axion
S.J. AsztalosG. CarosiC. HagmannD. Kinion,
K. van BibberM. Hotz
L.J. RosenbergG. Rybka, J. HoskinsJ. HwangP. SikivieD. B. TannerR. BradleyJC
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Our Bizarre Universe
Neutrinos 0.6%
Baryons (ordinary matter) 4.6%
Dark Energy (DE) 73%
Cold Dark Matter (CDM) 22%
• A candidate particle for CDM is the axion, proposed in 1978 to explain
the absence of a measurable electric dipole moment on the neutron
• Roberto Peccei and Helen Quinn 2013 J.J. Sakurai Prize
• An alternative candidate particle is the WIMP—Weakly Interacting
Massive Particle
• Blas Cabrera and Bernard Sadoulet 2013 W.K.H. Panofsky Prize
0 100 200 300 400 500 6000
100
200
300
400
2.73K
Inte
nsi
ty (
MJy
sr-1
)
Frequency (GHz)
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Po
wer
Frequency
610~ −−−−∆∆∆∆
νννν
νννν
Resonant Conversion of Axions into PhotonsPierre Sikivie (1983)
Primakoff Conversion
Expected Signal
HEMT* Amplifier
*High Electron Mobility Transistor
Magnet
Cavity
• Predicted axion mass:
ma ≈ 1 µeV – 1 meV (0.24 - 240 GHz)
• Need to scan frequency
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Axion Dark Matter eXperiment (ADMX)
• Cooled to 1.5K
• 7 tesla magnet
Originally: Lawrence Livermore
National Laboratory
Now: University of Washington,
Seattle
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Amplifier Noise Temperature
-AR
Ti
( )[ ]RRTT4kA(f)S NB
20
V +⋅=
V0
Quantum limit: TQ = hf/kB
i
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LLNL Axion Detector
• Original system noise temperature: TS = T + TN ≈ 3.2 K
Cavity temperature: T ≈ 1.5 K
Amplifier noise temperature: TN ≈ 1.7 K
• Time to scan the frequency range from f1 = 0.24 to f2 = 0.48 GHz:
τ(f1, f2) ≈ 4 x 1017(TS/1 K)2(1/f1 – 1/f2) sec
≈ 270 years
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Microstrip SQUID Amplifier: Principle
Conventional SQUID Amplifier Microstrip SQUID Amplifier (MSA)
• Source connected to both ends of coil • Source connected to one end of the
coil and SQUID washer; the other end
of the coil is left open25
20
15
10
5
Gai
n (
dB
)
20015010050Frequency (MHz)
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MSA Gain Measurements
600
400
200νre
s (M
Hz)
604020Coil Length (mm)
30
25
20
15
10
Gai
n (
dB
)
700600500400300200100
Frequency (MHz)
71 mm
33 mm
15 mm
7 mmGai
n (
dB
) νre
s (M
Hz)
Gain for four coil length
M. Mück, J. Gail, C. Heiden†, M-O André , JC
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MSA Noise Temperature vs. Bath Temperature
Gain = 20 dB
Quantum limit TQ = 30 mK
TQ
Tbath = 50 mK
Noise temperature:
TNopt = 48 ± 5 mK
Darin Kinion, JC
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MSA:Impact on Axion Detector
≈≈≈≈ 100 days
• Original LLNL axion detector: TS ≈ 3.2 K
• Microstrip SQUID amplifier: TN ≈ 50 mK
• Next generation: Cool system in a dilution refrigerator to 50 mK
• For T ≈ TN ≈ 50 mK: TS ≈ T + TN ≈ 0.1 K
• Scan time ∝ Ts2 :
τ(0.24 GHz, 0.48 GHz) ≈ 270 years x (0.1/3.2)2
• ADMX II now funded at the University of Washington by DOE
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Epilogue
• SQUIDs are remarkably broadband: 10−4 Hz (geophysics)
to 109 Hz (axion detectors).
• At low temperatures, the resolution of SQUID amplifiers is essentially limited by Heisenberg’s Uncertainty Principle.
• SQUIDs are amazingly diverse, with applications in
physics, chemistry, biology, medicine, materials science,
geophysics, cosmology, quantum information,……..
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Brian: Thanks and
Congratulations!
Then…
…and Now