can dt cmb /dt be measured?

Can dTCMB/dt be Measured?

R. V. DuncanUniversity of New Mexico, and Caltech

Quarks to Cosmos WorkshopAirlie Center, May 23, 2006

Work sponsored by NASA, and by and equipment loan from Sandia National Labs

Acknowledge helpful discussions with Prof. George Seidel (Brown) and Prof. Philip Lubin (UCSB)

Why?• Fundamental test of cosmological theories• Hubble’s Law: v = H D

– H is very uncertain, 45 – 90 km/s per Mpc– T-1 dT/dt ~ D-1 dD/dt = v / D = H, hence a direct

measurement of Hubble’s Constant.

• Vastly improved long-baseline stability for all space radiometry applications– Quasar / Black Hole / etc. radiation variation – Anisotropy stability studies

• Anticipate dTCMB/dt ~ 200 pK/year

An Exceptionally Hard Experiment

Photon Collection from a faint 2.7 K source:To resolve T/T ~ 10-11 requires Averaging time ~ one month

Foreground Sources:Hubble Ultra - Deep Field:SW of Orion in Constellation Fornax,chosen for sparce foreground sources.

0.05 arc degrees

Metrology: BB stable to within 100 pK over decades!

New Ultra-Stable Platform

C. J. Green, D. A. Sergatskov, and R. V. Duncan, J. Low Temp. Phys. 138, 871 (2005).

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2

1. Paramagnetic Susceptibility Thermometry

Magnetic flux is trapped in aniobium tube

A paramagnetic substance with T > Tc is thermally anchored to the platform

M = H (T)

[(T – Tc)/Tc]- so small changes in T create large changes in M

Gifford, Web, Wheatley (1971)Lipa and Chui (1981)

PdMn: Klemme et al., JLTP 116, 133 (1999) Nelson, Sergatskov, & Duncan, JLTP 127 173 (2002)

H

Pd Mn

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Temp (K)

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35 G

150 G

250 G

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Temp (K)

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Decreasing T - 6gauss

Increasing T - 6 gauss

Decreasing T - 35gauss

Increasing T - 35gauss

PdMn0.9% Thin Film Magnetic Susceptibility ThermometrySee R.C. Nelson et al., JLTP (2002) For thermometry, See Duncan et al., 2nd Pan Pacific Basin Workshop, 2001.Thin film sensitivity vs. T and H No hysteresis was observed

Fundamental Noise Sources

Heat fluctuations in the linkone independent measurement per time constant = RC(noise)2 / C(TQ)2 = 4RkBT2

so TQ √R and TQ TSee: Day, Hahn, & Chui, JLTP 107, 359 (1997)

Thermally induced electrical current fluctuationsmutual inductance creates flux noise()2 T N2 r4 / L M = / s, s ≈ 1 so M √T

SQUID noise(SQ)21/2 ≈ 4 √Hz with shorted inputexternal circuit creates about three times this noise levelso ≈ 12 √Hz and SQ ≈ 12 pK/√Hz

T, C Tbath

R

r

N

L

Heat Fluctuation Noise Across the Link

R = 40 K/W

(TQ)2 = 4RkBT2

so TQ = 0.10 nK/√Hz

3 dB point at 10 Hz,suggesting ≈ 50 ms

(collaboration with Peter Day)

HRT Time Constant

Method:

• Controlled cell temperature with T1

• Pulsed a heater located on T2

• Cell in superfluid state

• Contact area of only 0.05 cm2

• Rise time ~ 20 ms

• Decay time = 48 ms

Collaboration with Peter Day

Reduce the Heat Fluctuation Noise

Reduce R from 40 to 0.25 K/W

Now TQ ≈ 7 pK/√Hz

Minimize TM with a gap toreduce mutual inductance to the SQUID loop

is PdMn thickness = 0.76 mm

r4 4 r 3 r3/(43) ≈ 18

The Cryostat

Typical Noise Spectrum, T = 1.6 K

Data: 30 min. at 10,000 points / sFFT: MATLAB ‘pwelsh’T 25 pK/√Hz

Thermally Driven Electric Current Fluctuations

Thermal current fluctuations: = 38 /(Hz K)1/2 √SQUID circuit noise: SQ = 12.5 /√Hz

2. RF-biased Josephson Junctions for Heater Control

Vn = n (h/2e) fh/2e = o = 2.07 V/GHzf = 94.100000000 GHzRel = 1,015 Pn = Vn

2 / Rel = 37.3 n2 pW

Standoff vs. Josephson Quantum Number

Rel = 1,015

Rso = 4,456 K/W

Tcool

T

Rso

n = 7

n = 10

n = 0

A New ‘Fixed-Point’ Standard

T = T – 125 K

Conclusions• Fundamental noise sources in PST

identified and reduced• Lowest noise 25 pK/√Hz at 1.6 K• New rf-biased Josephson junction heater

controller developed• Technology in place now to develop a BB

reference standard more stable than the CMB temperature (< 200 pK/year drift) in a weightless lab, provided that T does not vary with the cosmic expansion

0

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1.5 2 2.5 3 3.5 4

Temp (K)

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ns

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ta/m

K)

6 G

35 G

150 G

250 G

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5

10

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35

40

1.5 2 2.5 3 3.5 4

Temp (K)

Se

ns

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(fl

ux

qu

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ta/m

K)

Decreasing T - 6gauss

Increasing T - 6 gauss

Decreasing T - 35gauss

Increasing T - 35gauss

PdMn0.9% Thin Film Magnetic Susceptibility ThermometrySee R.C. Nelson et al., JLTP (2002) For thermometry, See Duncan et al., 2nd Pan Pacific Basin Workshop, 2001.Thin film sensitivity vs. T and H No hysteresis was observed

New Data, PdMn0.4%, 6.67 m thick films

Tc=1.17 ± 0.01 K

= 1.41 ± 0.01

Data by… Ray NelsonColin GreenDmitri SergatskovR. V. Duncan