SQUID characterizationof materials

SQUID characterizationof materials

SQUID surveying for minerals

SQUID characterizationof materials

SQUID surveying for minerals

SQUIDsscreening

for ischemia

SQUID characterizationof materials

SQUID surveying for minerals

SQUIDsscreening

for ischemia

Gravity probe B:SQUID gyroscopes

The Ubiquitous SQUID: From Cosmology to Medicine

BCS@50UIUC12 October 2007

• The SQUID: A little history

• Cosmology-Shedding light on dark energy-Searching for cold dark matter

• Medicine-Magnetoencephalograpy-Microtesla magnetic resonance imaging

Supported by DOE

In the Beginning…..• Fritz London understands that the electrons in a

superconductor are in a macroscopic quantum state• He predicts that magnetic flux in a closed superconducting

ring is quantized in units of h/e• BCS formulate the ground state wave function for the pair

condensate, which can be described by a single macroscopic quantum state

Ψ(r,t) = |Ψ(r,t)|eiφ(r,t)

Φ = n Φ0

J

Flux QuantizationSingle-valuedness of Ψ:Φ = nΦ0 (n = 0, ±1, ±2, ...)whereΦ0 ≡ h/2e ≈ 2 x 10-15 Tm2

is the flux quantum

Deaver and Fairbank 1960 Doll and Näbauer 1960

Vibrating s/c tube in a coil

Torque on a s/c tube

In the Beginning II…..• Ivar Giaever observes single electron tunneling between

superconductors• (Morel) Cohen, Falicov and Phillips formulate their tunneling

Hamiltonian• At Cambridge University, Phil Anderson describes this theory

in a lecture course in which Brian Josephson is a first year graduate student

JosephsonTunneling

Anderson and Rowell 1963

Sn-SnOx-Pb1.5 K

0.006 G

0.4 G

I

Superconductor 1 Superconductor 2

~ 20 Å

Insulatingbarrier

I

V

I = I0 sinδδ = φ1 – φ2

dδ/dt = 2eV/ħ= 2πV/Φ0

Josephson 1962

Birth of the SuperconductingQuantum Interference Device (SQUID)

Jaklevic, Lambe, Silver and Mercereau 1964

Critical curent versus applied magnetic field for two different junction spacingsRapid oscillations due to interference, slow oscillations due to diffraction

Sn-SnOx-Sn junctions

VΦ

I

Zimmerman and Silver 1966

Other SQUIDDesigns

Niobium structures

5 mm

Copper

Niobium

SnPbsolder

The SLUG(Superconducting Low-Inductance Undulatory Galvanometer)Autumn 1964: Brian Pippard suggests that a quantum interference

device would make a sensitive voltmeter

Current IB in niobium wireV

olta

ge

JC 1966

Nb wire and solder

I

I

V

IB

IB

5 mm

Copper

Niobium

Solder

The SLUG as a Voltmeter

Voltage noise10 fVHz-1/2

V

JC 1966

1 μΩ

Beasley and Webb 1967

0.001′′ Nb foil

0.001′′ mylar

0.03′′ Nb wire

Adjustable Niobium SQUIDNb wireand foil

Silver and Zimmerman 1967

The RF SQUID

L

M

Thin-Film Cylindrical SQUID

5 mm

Wolf Goubau, Mark Ketchenand JC 197410-14 tesla Hz-1/2 (10 fTHz-1/2)

• Nb-NbOx-PbInjunctions

• Shadow masks

Thin-Film DC SQUID

Ketchen and Jaycox 1982

Superconductingwasher

• Pb alloy• Photolithography

Nb-AlOx-Nb Tunnel Junctions

Rowell et al. 1981

Trilayer process

• Deposit Nb film as base electrode• Deposit Al film• Grow AlOx layer thermally in O2• Deposit Nb film as counter electrode

Standard process for all low-Tc electronics

The Workhorse SQUID

SQUID with input coil Josephson junctions

500 μm 20 μm

Multilayer device with photolithographic patterning Niobium - aluminum oxide – niobium Josephson junctionsOperates typically at temperatures ≲4.2 K

Flux Noise in the SQUID

Frequency (Hz)

White noise2 x 10-6 Φ0 Hz-1/2S Φ

(f) (

H

z-1)

2 0Φ

10-1 101 103 105

10-10

10-12

V

0 1 2 Φo

Φ

δV

δΦ

Noise in the dc SQUID

Originates in Nyquist noise in shunt resistors R.

For SQUID with optimized parameters and inductance L:

Computed spectral density of flux noise SΦ(f) ≈ 16kBTL2/R

For L = 200 pH, R = 6 Ω, T = 4.2 K:

2/1062/1 Hz10x2.1)f(S −−≈ ΦΦ

ε f( ) = SΦ f( ) / 2L ≈ 10−32 JHz−1 ≈ 100h( )

Noise energy:

Claudia Tesche and JC 1977

Superconducting Flux Transformer:Magnetometer

SQUIDMagnetic field noise ~ 10-15 THz-1/2

B J

Closedsuperconducting

circuit

Roomtemperatureelectronics

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

High-Tc SQUID

Ludwig et al. 1995

• YBCO films and bicrystalgrain boundary junctions—which are not very reproducible

• White noise and 1/f noisehigher than for low-Tc SQUIDs

• No flexible, bondable high-Tcwire technology

Cosmology

Neutrinos 0.6%Baryons (ordinary matter) 4.6%Cold Dark Matter (CDM) 22%Dark Energy (DE) 73%

• Thus 95% of the universe is unknown!• SQUIDs are being used to investigate both DE and CDM

Cosmic Microwave Background (CMB)“The Cosmic Rosetta Stone”

Transition-Edge Sensor (TES)

SQUID

250 mK

TES

Weakthermal link

Optical absorber

T

R

• Electrothermal feedback: fast, linear response• Low power dissipation (~1 nW)• Sensitivity limited by photon shot noise

Kent Irwin

Shedding Light on Dark Energy: Searching in the FIR for Galaxy Clusters

• South Pole Telescope (SPT) Antarctica • 1000 transition edge sensors with

multiplexed SQUID readoutUCB, LBNL, Univ. of Colorado Boulder, Univ. of Chicago, Case Western Reserve Univ.,UC Davis, Harvard-Smithsonian, Univ. of Illinois, Jet Propulsion Laboratory

• James Clerk Maxwell Telescope, Mauna Kea, Hawaii

• 10,240 transition edge sensors with multiplexed SQUID readoutAstronomy Technology Center (UK),NIST (US), multiple universities

Searching for Cold Dark Matter

• A candidate particle is the axion, proposed in 1978 toexplain the absence of a measurable electric dipolemoment on the neutron

ma ≈ 1μeV – 1 meV (0.24 - 240 GHz)• Predicted axion mass:

UC BerkeleyLLNLUniversity of Giessen

Pow

erFrequency

610~ −Δνν

Resonant Conversion of Axions into PhotonsPierre Sikivie (1983)

Primakoff Conversion

Expected Signal

HEMT* Amplifier

*High Electron Mobility Transistor Need to scan frequency

Magnet

Cavity

Axion Detector at Lawrence Livermore National Laboratory

• Cooled to 1.5K• 7 tesla magnet

Scan Time

• Using a HEMT amplifier, time* to scan the frequency range

from f1 = 0.24 to f2 = 2.4 GHz: 45 years

*Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) theory

Noise Temperatures of Two SQUID Amplifiers

TQL = 33mK

• In the classical limit theory predictsTN ∝ T• In the quantumlimit: TQL = hf/kB• Closest approachto quantum limit:At 799 MHzTN = 47 ± 5 mKTQL = 38 mK

University of California, BerkeleyLawrence Berkeley National LaboratoryLawrence Livermore National LaboratoryUniversity of Giessen

684 MHz

702 MHz

HEMT TN ≈ 2 K

Scan Time

• Using a HEMT amplifier, time* to scan the frequency range

from f1 = 0.24 to f2 = 2.4 GHz: 45 years

• The HEMT is being replaced with a SQUID amplifier. With the

system cooled to 50 mK by a dilution refrigerator, time* to

scan the frequency range from f1 = 0.24 to f2 = 2.4 GHz: 18 days

*Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) theory

Medicine

300-Channel SQUID Systems for Magnetoencephalography (MEG)

• Presurgical mapping of brain tumors• Locating epileptic centers• Monitoring recovery from stroke or brain trauma

MicroteslaMagnetic Resonance Imaging

UC BerkeleyLBNL

High Field Magnetic Resonance Imaging

1.5 tesla MRI scanner (GE)

Could we lower the magneticfield by a factor of (say) 10,000 to 150 microtesla?

Microtesla MRI System

• Protons are prepolarized in afield of typically 50–100 mTprior to obtaining the image.

• Typical imaging field is 132 μT(proton frequency 5600Hz).

• Three magnetic field gradients define “voxels” in the sample.

• NMR signal is detected with aSQUID gradiometer with a noiseof 8 ×10−16 T Hz−1/2.

T1-Weighted Contrast Imaging

• T1 is the relaxation time for the nuclear spins to returnto thermal equilibrium after a π/2 pulse, and is typically 1 sec in water. It depends strongly on the environment.

• T1-weighted contrast imaging is used in conventional MRI to distinguish different types of tissue.

• However, contrast is sometimes very poor, for example for breast tumors, unless one uses an injected contrast agent such as a Gd compound.

• T1-contrast cannot be achieved for prostate tumors evenwith a contrast agent.

• T1-contrast can be much higher in low fields.

Enhanced T1-Weighted Contrast

Phantom:Water columns in agarose gel

S-K. Lee et al.

T1 contrast at 132 µT

2

T1 contrast at 100 mT

1

Preliminary Measurements on Ex Vivo Prostate Tissue

• Malignant prostate removed surgically at UCSF hospital• Pathologist cuts two small tissue samples, one healthy and one

cancerous (Blind: we do not know which is which)• Samples rushed to Berkeley in a biohazard bag placed on ice• About two hours after surgery, T1’s of the two samples are

measured simultaneously• Based on results from eight pairs of such specimens, we find

that T1 in healthy tissue is typically 60% higher than in tumors

Prospects• Microtesla MRI is potentially lower in cost, lower in weight,and more open than conventional MRI.

• It has the particular advantage of significantly higher T1-contrastthan high-field MRI.

• Next step is to build a prototype system for in vivo imaging oftumors: Projected resolution 2 × 2 × 2 mm3.

• Microtesla MRI may have application to screening for cancer, and to monitoring the progression of tumors during treatment.

• A new EU project is aimed at combining microtesla MRI with existing 300-channel systems for magnetoencephalography.

Epilogue

• SQUIDs are very diverse, with applications in physics, chemistry, biology, medicine, materials science, geophysics,cosmology, quantum computing,……..

• SQUIDs are remarkably broadband: 10-4 Hz (geophysics)to 109 Hz (axion detectors).

• The resolution of SQUID amplifiers approaches the quantum limit.

• The SQUID, now 44 years old, shows no signs of aging. New devices are on the horizon, including “nanoSQUIDs” to detect the magnetic moments of single molecules and quantum limited readout schemes for superconducting quantum bits (“qubits”).