1. Ubiquitous Superconducting Sensors in Cosmology
卓筱梅
Hsiao-Mei (Sherry) Cho
National Institute of Standards and Technology, Boulder, CO, USA
Friday March 5, 2010
Department of Physics
National Chung-Hsin University, TaiChung, Taiwan

2. Outline Introduction Transition Edge Sensor (TES)
Superconducting QUantum Interference Device (SQUID)
Part I: Looking for CMB polarization
Polarimeter design and results
Projects
Part II: Help wanted
Superconductivity
Thermodynamics
Material science
Future plans

3. Superconductivity I I A macroscopic quantum state
Condensate of Cooper pairs
Charge 2e, k = 0, s = 0
Zero resistance
Supercurrent is carried by
Cooper pairs and generates
no voltage or dissipation. I I
F = n F0 J
Flux quantization
Single-valuedness of Y:
F = nF0 (n = 0, ±1, ±2, ...)
where
F0 ≡ h/2e ≈ 2 x Tm2
is the flux quantum

4. Typical R vs T dT dR

5. Josephson Tunneling Brian Josephson 1962
Cooper pairs tunnel through a barrier I
Superconductor 1
Superconductor 2
~ 20 Å
Insulating
barrier V
I = I0 sin
= 1 – 2
d/dt = 2eV/ħ
= 2V/0 1 2 V I
Oxidized Nb film
Nb film V I

6. The dc Superconducting Quantum Interference Device
Current-voltage (I-V) characteristic modulated by magnetic flux F
Period one flux quantum F0 = h/2e ≈ 2 x T m2
DC SQUID
Two Josephson junctions on a superconducting ring I F V I n F
(n+1/2) DV V Ib V dV dF F F 1 2

7. Thin-Film DC SQUID Operates typically at temperatures ≲4.2 K
Multilayer device
Niobium - aluminum oxide – niobium Josephson junctions
500 m
20 m
SQUID with input coil
Josephson junctions

8. Spectral Density of Flux Noise in a dc SQUID
10-9
10-10
10-11
10-12
10-13
L  0.2 nH
R  6 
T  4.2 K
S(f) ( Hz-1) 2 Φ
White noise
2 x 10-6 0 Hz-1/2
10-1 1
101
102
103
104
105
Frequency (Hz)

9. Magnetic Fields tesla Conventional MRI 1 10-2 10-4 Earth’s field 10-6
Urban noise
Car at 50 m
Human heart
Fetal heart
Human brain response
SQUID magnetometer
Conventional MRI
Magnetic Fields
10-16
10-10
10-8
10-6
10-4
10-12
10-14
10-2 1
1 femtotesla

10. Voltage-Biased Transition-Edge Sensor (TES) Bolometer
Optical absorber R
TES
SQUID
Weak
thermal
link T
Ptotal = Popt + Pelc = constant
250 mK
Electrothermal feedback: fast, linear response
Low power dissipation (~1 nW)
Sensitivity limited by fluctuations in the photon arrival rate

11. Looking for CMB polarization

12. The universe we know CMB = cosmic microwave background
Thermal radiation in the early universe scattered off of the plasma until it neutralized (after 380,000 years)
At this time, the universe is opaque to photons before 380,000 years: but not to gravitational waves and neutrinos
Gravity waves from the Big Bang made the thermal radiation hotter in one direction (anisotropy). When anisotropic radiation scatters, it is polarized.
By measuring the polarization of the CMB, we can detect the imprint of gravity waves from the Big Bang, allowing us to directly probe the inflationary era.
Detection of the cosmic gravity wave (CGB) background would probe the inflationary era (10-35 s?)
Direct probe of inflation vs. cyclic / ekpyrotic models
Grand Unification scale physics
Courtesy of WMAP

13. Anisotropies from gravitational waves
Gravity waves make a uniform temperature distribution appear hotter in one direction (anisotropy), resulting in polarization.
We consider the primordial plasma as an array of test masses in a giant gravitational radiation detector

14. Gravity wave signature
Simulation of CMB polarization signal with no gravity waves
The “curl” of the polarization is zero.
No gravity waves
Simulations from SPIDER collaboration

15. Gravity wave signature
Simulation of CMB polarization signal with gravity waves
The “curl” of the polarization is nonzero: gravity waves!
Gravity waves!!!
No Tensor
Simulations from SPIDER collaboration

16. The state of the field
100 GHz
150 GHz
BICEP

17. … but orders of magnitude improvement in mapping speed needed.
The state of the field
l(l+1)Cl/2p (mK2)
… but orders of magnitude improvement in mapping speed needed.

18. TES for CMB polarimetry
University of Chicago
J.A. Beall D. Becker
J. Britton G.C. Hilton
J. Hubmayr K.D. Irwin
M.D. Niemack K.W. Yoon
B.A. Benson L. E. Bleem
C. L. Chang A.T. Crites
W. Everett J. McMahon
J. Mehl S.S. Meyer
J.E. Carlstrom
CU-Boulder
Princeton University
J.E. Austermann
N.W. Halverson J.W.Henning
S.M. Simon
J. W. Appel L. P. Parker
T. Essinger-Hileman Y. Zhao
S. T. Staggs C. Visnjic

19. 150 GHz CMB polarimeter fabricated at NIST
Filter design
4/
150 GHz CMB polarimeter fabricated at NIST
TES
Heater
Gold meander
TES A Si
Tbath = 0.3K
SiN Nb
MoCu TES
Tc ~ 530 mK
TES B
TES D
OMT design
CPW to
microstrip
transition
5 mm
Components designed by NIST, CU-Boulder, University of Chicago and Princeton University

20. CPW to microstrip transition
OMT design
CPW to microstrip transition
HFSS = high frequency structure simulator
smooth transition from CPW (~70 Ohm) to microstrip (~10 Ohm)

21. Microstrip stub filters design
/4 shorted stub bandpass filters
Stepped impedance low-pass filters
HFSS = high frequency structure simulator

22. Lossy gold absorber
HFSS = high frequency structure simulator
Nb-to-Au transition is well-matched --- low reflection loss

23. Voltage-Biased Transition-Edge Sensor (TES) Bolometer
Optical absorber R
TES
SQUID
Weak
thermal
link T
Ptotal = Popt + Pelc = constant
250 mK
Electrothermal feedback: fast, linear response
Low power dissipation (~1 nW)
Sensitivity limited by fluctuations in the photon arrival rate

24. Optical power vs Tbath
Ptotal = Popt + Pelec (70% Rn)

25. Noise performance
(4kGTC2)1/2

26. FTS bandpass measurements
Run 1
Run 2
Run 3
5 GHz
Run 1:
5 GHz shift due to assuming er = 4.2
Run 2:
After correction, measured and predicted bandpass ( GHz) agree
Run 3:
Measured and predicted bandpass ( GHz) agree

27. CMB polarization: possible pixel schematic
Au plated Si feed horns
2 mm
Polarimeter
wafer
Backshort
wafer
5 mm

28. Prototype array Si feedhorns 4 inch
Future projects require 7 wafers, ~ 1300 TESs

29. Telescope Polarimeter
Instruments in development
South Pole Telescope
Polarimeter
SPTPol
Atacama Cosmology
Telescope Polarimeter
ACT-pol
Atacama B-mode Search
(ABS)
Atacama, Chile
2010
South Pole
2012
Atacama, Chile
2012

30. Help Wanted

31. Superconductivity Longitudinal proximity effects Tc vs Rn
J.E. Sadleir et al, GSFC, PRL 104, (Jan 2010)
Longitudinal proximity effects
Tc vs Rn
Magnetic effects in Tc

32. Thermodynamics In each pixel NIST design Nb leads P = K (Tcn – Tbathn)
Cu bank
500 nm
Mo/Cu TES
Nb leads
In each pixel
P = K (Tcn – Tbathn)
G = dP/dTc
350 mm
0 = C/G where C is heat capacity
120 μm
NIST:
TES Intrinsic time constant:  tes = 7-10 ms
UC-Berkeley:
TES Intrinsic time constant:  tes = 50 μs
TES + Bling time constant:  0 = C/G = 20 ms
Decoupling time:  int = 400 ms
UC-Berkeley design

33. Material Science Stress in thin films Loss in dielectric material
Damaged suspended SiN membrane
Change Tc of TES
Curve Si wafer
Loss in dielectric material
Shift bandpass
Lower efficiency

34. High frequency leak High frequency leak
Unfortunately we have not figured out the cause yet.

35. Future Plans
Continue detailed optical and dark characterizations of CMB prototype pixels through summer Finish measurements of 145 GHz Si feed; iterate on design Extend existing design concept to 90/220 GHz Si feed array (with 3” monolithic detector array) soon. 240 single-pixel polarimeters for ABS (deploy to Atacama in early 2010) 6” monolithic focal planes (~640 pixels) delivery for SPTpol & ACTpol by late 2011.

36. Thank you for your attention!!