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Casimir ESF Meeting Nov 2008
Experimental Gravitation and the Casimir force at University of Birmingham
Clive Speake
Casimir ESF Meeting Nov 2008
What do we do?
• Development of techniques for weak force physics: interferometers, room temperature and superconducting suspensions.• Search for new forces coupling mass to spin. • Searches for deviations from the inverse square law at short ranges.• Precision measurement of the Casimir force at
4 K.
Casimir ESF Meeting Nov 2008
Instruments for searching for short range forces
Adelberger and colleagues, the Eot-wash collaboration.
Mass separation 56 μm with 10 μm shield.
Gold TestMass
Au/SiDrive Mass
Mass separation 25 μm with 3 μm shield.
Kapitulnik and colleagues
AFM’s Mohideen, Chevrier.
Casimir ESF Meeting Nov 2008
Instruments for searching for short range forces
H-J Paik University of Maryland
Cryogenic expt, source mass motion of +/-50μm
Vibrating source plane disk
Test masses
12.5μm Superconducting
shield
Cold Atom methods eg Ferrari et al PRL 2006
Bloch Oscillations
ν= mgλ/2h
Casimir ESF Meeting Nov 2008
Spherical Superconducting Torsion Balance (Mk1 SSTB)
Key Features
• Meissner Effect Suspension
• Spherical Symmetry
• Programmable Stiffness
(τ=200s-20s)
• SQUID Angular Readout
(2x10-13Nm/√Hz)
• Optimised for Short Ranges
• Based on Lead
Float
Levitationbearing
Rotationdetector
Review of Scientific Instruments, 75, pp 955-961, 2004.Precision Engineering, 24, pp 139-145, 2000.
Measurement Science and Technology, 10, pp508-513, 1999.
Casimir ESF Meeting Nov 2008
Search for new forces coupling mass to
intrinsic spin.
Γ=(-5.4±(3.8)stat±(4.2)sys)x10-15Nm=(-5.4 ±5.7) x10-15Nm
gpgs=(-1.9±(1.3)stat±(1.5)sys)x10-26Nm=(-1.9 ±2.0) x10-26 for λ>10mm
Most conservative limit assumes gpgs is -3.9 x10-26 for λ>10mm
Physical Review Letters, 98, 081101, 2007
Casimir ESF Meeting Nov 2008
Preferred Frames Lab• Cosmic pseudo-magnetic field that couples to intrinsic spin. Predicted as a consequence of including long range space curvature in Standard Model (Kostelecky).
• Is G anisotropic?
• Large mass helps for long range experiments !
Casimir ESF Meeting Nov 2008
Torsion strip balance ‘G-machine’ at BIPM
1.2kg test massesAutocollimator
Carousel for 12kg source masses
PRL 2001
Casimir ESF Meeting Nov 2008
Tilt insensitive interferometer for inertial control of drag-free satellites
CCS and S.M.Aston Class. Quantum Grav. 22, S269-S277 2005S.M.Aston and CCS P326-333. 6th International LISA Symposium 2006
Casimir ESF Meeting Nov 2008
Tests of Newton’s inverse square law
• The signature for the breakdown of ISL can be parametrised as:
iRr ≥( )λ−α+−= /3 1 rermG
V
•• Many other theoretical predictions to be tested:
•• SLED theory to explain the Cosmological constant requires violation at 14 mm (C.P.Burgess, arXiv:hep-th/0411140
(2004).
• Chameleons: mass is derived from curvature of underlying potential, again solution to Cosmological constant problem
• Moduli, dilatons, axions…
Casimir ESF Meeting Nov 2008
LED hypothesis: Relationship between New Mass scale for Unification, M*, and R radius of compact
dimensions:
-7 -6 -5 -4 -3-1
1
3
5
7
9
11
Log1
0(M
*) [G
eV]
Log10(R) [m]
n = 1 n = 2 n = 3
LHC scaleDark Energy scale
N.Arkani-Hamed, S.Dimopoulos and G.Dvali, Physics Letters B 429 pp263-272 (1998)
Casimir ESF Meeting Nov 2008
Conceptual design of Birmingham experiment
Low-density AlHigh-density Au
Motion
one mass is cylindrical to avoid tilt sensitivity around θ
Au coating
NbNb No No electrostatic electrostatic shield as used in shield as used in previous previous exptsexpts!!!!
Measure induced torque
Casimir ESF Meeting Nov 2008
Candidate Systematic Effects Seed-corn sensitivity= 2x10-17N 100days integration
Background B0 field<30μT
Magnetic force due to permeability contrast
0.1μm and 0.5mV to give target sensitivity
Electrostatic force due to Pot. Diff. and corrugations
Diffusivity of Au/Cu
as aboveContact potential
Negligible.Patch-fields
Coherent corrugation amplitude b<30nm;
Casimir force due to corrugations
Δλp ∼10%gives 3x10-20N
Casimir force due to material modulation
Critical parameterForceSource
zzSl
zc
Λ⎟⎠⎞
⎜⎝⎛
⎟⎠⎞
⎜⎝⎛ 22/1
3
2 212863
720λπ h
aap eSa
lv /2
32
022
2π−⎟
⎠⎞
⎜⎝⎛ π
πε
( ) ( )2/5
2/12
2102 2
zslVAA
Λεπ
( )( )∫
− +μχΔχΔ 2/
2/2
0
2021
2sinh2
w
w Ryzkdyl
B
zS
zbl
zc 2
256420
720
22
3
2 πΛ
π⎟⎟⎠
⎞⎜⎜⎝
⎛h
Casimir ESF Meeting Nov 2008
STFC funded next step:to test of ISL at 10μm
– Redesign the suspension !!!– Improve read-out signal/noise using
interferometer.– Isolate from ground vibrations using active
isolation.– Reduce float magnetic moments using
annealing.– Improve cryogenic technology using cryocooled
dewar. – Optimise test mass geometry.– Improve test mass manufacture and finishing:
use optical polishing (σ∼ 0.1 μm) of masses in rigid substrates.
Casimir ESF Meeting Nov 2008
‘Shortcomings’ of Casimir’sanalysis
• Thermal CorrectionWhen , corresponding to d=7μm at room temperature, real black body photons produce a real pressure. Controversy over the entropy at zero temperature!
• Roughness correction.
• Modelling reflectivity of real metals.
• Electrostatic forces due to patch-potentials.
kTcd h≈
Reynaud and Lambrecht et al 2001
Casimir ESF Meeting Nov 2008
Slip-stick-piezo drive
Au coated 12 cm radlens and plane
SSTB in Casimir configuration
Casimir ESF Meeting Nov 2008
1 2 3 4 5 6 7 8-0.1135
-0.113
-0.1125
-0.112
-0.1115
-0.111
-0.1105
-0.11
approx distance um
serv
o cu
rrent
A
First raw data set 19/12/07
Fit to 1/r3
Preliminary measurement of Casimir effect
Casimir ESF Meeting Nov 2008
Summary
• We are making progress with experimental tests of gravitation by using new instruments.
• We hope to make a measurement of the Casimir at 4K at d ~ few μm.
• We are now working towards a test of ISL at 10 μm.
Casimir ESF Meeting Nov 2008
Thanks to
• Ludivico Carbone, Hasnain Panjwani, Stuart Aston, Fabian Peña.
• Giles Hammond, Emanuele Rocco, Anthony Matthews.
Casimir ESF Meeting Nov 2008
Systematics notes Torque compared with nominal target of 6x10-19Nm
Casimir/ plasma wavelength Au/Cu 1.7x10-22
Casimir/corrugation* Corrugation amp=100 nm, surface separation 8 μm/ 1μm Au layer on each surface, force calculated to 10%
2.3x10-19
Electrostatic/corrugation Voltage difference 0.3 mV 1.6x10-19
Contact potential Contact potential 2 μV 3.3x10-19
diamagnetismAu/Cu with 4μT field
4x10-20
Newtonian force* Calculated to 10% 7x10-19
RMS 8.2x10-19Nm
Statistical uncertainty Torque noise compared with nominal level of 2x10-15Nm/Hz1/2
Float metrology Fractional ellipticity=10-3 Horizontal vibration spectrum 10-5ms-2/Hz1/2. Tilt adjustment 50 μrad of parasitic stiffness. 50g float.
1x10-15
Trapped flux 100 Gauss trapped field, Nb thin films. 1.3x10-20
Moment of inertia asymmetry 1% asymmetry 1.5x10-17
Read-out noise Interferometer with 1/f noise reduction of factor 120.
1x10-15
Thermal noise Q=104 5x10-16
RMS torque with 3 months integration time
1.5x10-15Nm/Hz1/2
=2.7x10-19Nm
TOTAL uncertainty8.6x10-19Nm
Casimir ESF Meeting Nov 2008
Commercialisation of compact tilt insensitive interferometer:
EUCLIDEUCLID
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