Experimental Gravitation and the Casimir force at ... · Experimental Gravitation and the Casimir...

Casimir ESF Meeting Nov 2008

Experimental Gravitation and the Casimir force at University of Birmingham

Clive Speake


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.


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.


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


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.


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


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 !


Torsion strip balance ‘G-machine’ at BIPM

1.2kg test massesAutocollimator

Carousel for 12kg source masses

PRL 2001


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


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…


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)


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


Mark II Spherical Superconducting Torsion balance


Tests of the inverse square law at short ranges.


Atomic force micrograph of Au surface


Tests of the inverse square law at short ranges.


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


Current limits for violation of the inverse square law.


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.


Future goal.

Maryland


‘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


Slip-stick-piezo drive

Au coated 12 cm radlens and plane

SSTB in Casimir configuration


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


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.


Thanks to

• Ludivico Carbone, Hasnain Panjwani, Stuart Aston, Fabian Peña.

• Giles Hammond, Emanuele Rocco, Anthony Matthews.


Thank you for your attention.


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


Commercialisation of compact tilt insensitive interferometer:

EUCLIDEUCLID


Homodyne interferometer for inertial control of drag-free satellites

4x10-9m/Hz1/2 at 0.03mHz

Shot noise limit of 10-13m/Hz1/2

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