STAR: Space-Time Asymmetry Research Testing Lorentz ... · LVG’12 Swarthmore October 13-14, 2012 1 Shally Saraf for the Stanford STAR team October 14, 2012 STAR: Space-Time Asymmetry

1 LVG’12 Swarthmore October 13-14, 2012

Shally Saraf for the Stanford STAR team

October 14, 2012

STAR: Space-Time Asymmetry Research

Testing Lorentz invariance in Low-earth orbit


STAR Concept

Science

1) Lorentz Invariance Violations

2) Velocity boost c dependence

“Kennedy-Thorndike Experiment”

3) >100x state of the art

Technology

1) “Capable” small satellite bus

180 kg, 185 W, secondary payload

2) Advanced frequency standards

3) Precision thermal control

Education

1) Graduate & Undergraduate

2) 3-5 year projects

3) Student led tasks

Science & Technology

on Small Satellites

Education driven

International collaborations

Lipa, et. al. “Prospects for an advanced Kennedy-Thorndike

experiment in low Earth orbit” arXiv:1203.3914v1[gr-qc]


STAR Collaboration

Collaborating Institutions

Main Contributions ALL

Science and EP&O

Ames Research Center

PM, SE, I&T, and SM&A

KACST

Spacecraft and Launch

Stanford University

PI and Instruments to TRL 4

German Space Agency et al

Instruments, Flight Clock

JILA

Instruments to TRL 4

Industrial Partner

Flight Instrument

Germany

German Aerospace Center (DLR)

ZARM & Bremen University

Humboldt University, Berlin

University of Konstanz

Kingdom of Saudi Arabia

King Abdulaziz City for Science

and Technology (KACST)

United States

NASA Ames Research Center (ARC)

Stanford University

Joint Institute for Laboratory

Astrophysics (JILA)

University of California-Davis

Industrial partner


STAR “Quad Chart”

SCIENCE What is the nature of space-time?

Is space isotropic?

Is the speed of light isotropic?

If not, what is its direction and

location dependency?

3×10-18 to 10-17

Mission design Circular sun-synchronous 650 km

circular orbit

180 kg,150 W

Launch 2015-2016

2-year lifetime

Class D Mission

Payload

Optical cavities ×4

0.1 K enclosure

I2 clocks ×2

Laser-based

comparator

BATC is payload consultant

Management

NASA Ames: PM, SE, SMA,

Mission Operations

Stanford: Science and Payload

KACST: Spacecraft and Launch

DLR: Payload Design & I2 Clock

ALL: Science & EPO


STAR Technology

Optical cavities

Molecular clocks

Hz10 15ff

Advanced frequency standards

Thermal shields

Control algorithms

Optical thermometry

12

9

10

10

shieldOutershieldInner

shieldOutershieldInner

FF

TT

nano Kelvin thermal control

STAR requires exquisite frequency standards and environmental

control, order of magnitude better than current state-of-the-art


Measuring LIV

HOW DOES ONE MEASURE CHANGES IN c?

KT coefficient

(function vINSTR) rod clock

(1) By comparing the length of a rod (measured by

light beam) to the rate of a ticking clock

(2) By comparing the length of two rods ‘perpendicular’

to one another (both measured with a light beam)

MM coefficient

(function INSTR)

rod 2 rod 1


STAR Conceptual Diagram


Why Measure c Invariance?

Colladay and Kostelecky (1997)

“The natural scale for a fundamental theory including gravity is

governed by the Planck mass MP, which is about 17 orders of

magnitude greater than the electroweak scale mW associated

with the standard model. This suggests that observable

experimental signals from a fundamental theory might be

expected to be suppressed by some power of the ratio:

1710~ P

W

M

mr

The STAR sensitivity could close the gap!


• Considers only light beams and ideal rods, clocks:

• If a laboratory is assumed to be moving at a velocity v relative to a preferred

frame, the speed of light as a function of the angle relative to the velocity

vector is given by

c()/c = 1 + (1/2 - b + )(v/c)2sin2 + (b - a - 1) (v/c)2

where a is the time dilation parameter, b is the Lorentz contraction parameter,

and tests for transverse contraction. (SR: a = -1/2; b = 1/2; = 0)

• Michelson-Morley : -dependent term

• Kennedy-Thorndike : -independent term

- Mansouri and Sexl (1977)

Kinematic approach to LIV

Simple but incomplete!


• Subset of Lorentz and CPT violating Standard Model Extension (SME)

- Colladay and Kostelecky 1990 - 2002

• Considers small violations that are potential remnants of Planck-scale physics

- subset considers Lorentz-violating quantum electrodynamics

- restricting to photon sector and renormalizable terms

- reduces to Maxwell equations plus two Lorentz-violating terms:

- one term CPT-odd(breaking), the other CPT-even(preserving)

- CPT-odd term known to be very small from radio galaxy polarization data

- CPT-even term less well-known

• Model has analogy with electrodynamics in a homogeneous anisotropic medium

- has links to Mansouri and Sexl kinematics, and relates to THεμ

-19 free parameters, 10 constrained by astrophysical observations

- Optical cavities sensitive to other 9 parameters

- Kostelecky and Mewes, 2002

Lorentz violations in the SME

Extended: Kostelecky & Mewes, 2009


• highly simplified example (K&M 2009):

• rods and clocks have effective metrics with

Lorentz violating parameters: cclock, crod

• obtain

b + - 1/2 = 7/12(crod)00 (MM style)

a - b +1 = - 7/12(crod)00 -5/12 (cclock)00 KT style)

• => KT measurements don’t reduce to MM measurements

except in special cases

• => MM and KT relate to the fermion sector (?)

MM and KT as subsets of the SME


(experiments need to specify species involved)

LV species-dependent fields

Turns out, precision length control of cavities is very hard and bulky.

Can we use two narrow transitions and do KT?

13 LVG’12 Swarthmore October 13-14, 2012 Brillet and Hall, PRL 1979

First ‘modern’ MM experiment


Peters, 2007

Crossed-cavity MM experiment

Improved MM experiment


Vertical Max Sensitivity

but …

Symmetry reduction ~200 x

(Tilt effects only quadratic)

Horizontal expect a reduction

but …

Observed Sensitivity ~ 1 x

(Tilt effect linear in angle)

Better? Airy Points ?

What about Horizontal Accelerations?

The problem with ‘g’

There may be better cavity support ideas?


a

L

0.01

0.1

1

10

5 6 7 8 9

12 3 4 5 6 7 8 9

102 3 4 5 6 7 8 9

1002

a = 0.11 * L

a = 0.577* L

MHz/ ms-2

2200 kHz/ms-2

150 kHz/ms-2

Frequency/acceleration sensitivity

17 LVG’12 Swarthmore October 13-14, 2012 17

STAR mission characteristics

ESPA compatible secondary payload on an EELV launch

Circular sun-synchronous ~ 650 km orbit

Launch 2015-2016

2-year mission lifetime


Sun-synchronous orbital motion

of STAR instruments

Sun

Earth

Orbital Motion


STAR KT-Style measurement


clock based on atomic transition

clock based on length standard

beat measurement

with

varying laboratory velocity

Modern KT style test configuration


Why KT in Space?

Kennedy-Thorndike signal enhancement

Signal modulated at satellite orbital variation ~1.5 hr

Signal modulated at orbital velocity differences 7 km/s

Diurnal Earth rotation signal <0.30 km/s @ 24 hr

Yearly Earth orbital motion signal at 30 km/s @ 8766 hr

Disturbance reduction Microgravity

Seismic quietness

Relaxed stress due to self weight

Far away from time dependent gravity gradient noises

KT Improvement in Space:

Faster signal modulation 4 (16)

Higher velocity modulation 20 to 30

Other considerations ~ 1 to 3

Net Overall Advantage 100


History of KT measurements

KT History

R.J. Kennedy E.M. Thorndike

KT

co

effic

ien

t

10-1

10-9

10-7

10-5

10-3

10-11

STAR 1

1920 1940 1960 1980 2000 2020

Year


STAR schedule, cost and status

Schedule

Three-year development

Two-year operations

Cost

Payload: ~ $ 50M

Total Mission: ~ $140M

Concept first proposed as a MOO 2008 SMEX

Second proposal submitted in 2011.

Review pointed out some weaknesses

Science, TRL levels

Current efforts:

Bring instrument to TRL 5

Using internal resources

Contributions from partners

Mitigate weaknesses of 2011 proposal


STAR Optical Setup & Noise Budget

Error Source KT MM

Optical Cavity – thermal expansion

(0.1microK temp. stability, 10–9 CTE)

1×10-16 1×10-16

Optical Cavity – mirror thermal noise (loss <

10–6)

7×10–16 7×10–16

Optical Cavity – residual gas pressure 4.2×10–19 4.2×10–19

Optical Cavity – shot noise (locking) 1.7×10–18 1.7×10–18

Optical Cavity – satellite spin rate stability

(Δω/ω < 0.025)

1×10–17 1×10–17

Optical Cavity – satellite pointing knowledge

(0.5 deg)

1×10–17 1×10–17

Total Molecular Clock 5×10–16 N/A

Frequency Shifter (comparator) 2×10–16 2×10–16

Total Error at measurement frequency with 2

clocks

6×10–16 2×10–15

Total Random Error after 2 year integration

time (Δc/c)

7×10–18 3×10–18

MARGIN 30% 70%


Optical cavity

Key optical cavity parameters:

L/L < 10-17 at orbit and harmonics

with 2 years of data

L/L < 10-17 at twice spin period

with 2 years of data

Derived requirements:

Expansion coefficient: < 10-9 per K

Operating temperature: within 1 mK

of expansion null (~ 15°C nom)

External strain attenuation: > 1012

Stiffness: L/L < 10-9 per g, 3-axis

Implied material: ULE glass Thermo- Mechanical

isolators

Support structure

Optical couplers

ULE cavity block

(4 cavities@ 45 deg)

26 LVG’12 Swarthmore October 13-14, 2012 Vortrag > Autor > Dokumentname > Datum

Iodine Reference


Next steps:

set up of a compact Iodine standard

multi-pass cell

baseplate made of Zerodur (for space-

qualification and pointing stability)

Using s.q. AI-Technology

(HTWG Konstanz / EADS Astrium)

Investigate resonantly enhanced interaction

in a short cell (Stanford)

Atomic reference


Thermal noise floor of cavities

State of the art: Iodine vs. cavity

Orbital period

STAR


Thermal enclosure

Main Requirements:

Thermal stability

Stress attenuation

Launch and space compatible

Multi-can structure

Thermal performance:

Cavity L/L < 10-17 (2 yr data) at:

- orbital period and harmonics

- twice spin period

Derived requirements (2 yr average):

Thermal stability of 10-8 K at orbit

Thermal gradient ~ 10-9 K/cm at orbit

Maintain cavities temperature to 1 mK


Thermal modeling of enclosure


Strain attenuation model - FEA

Estimated strain attenuation: > 103 per can

Extrapolating to entire enclosure: > 1015

Exceeds requirement by x1000


Fundamental frequencies

The first mode of the assembly was found to be 77 Hz

First lateral mode: 77.6 Hz First axial mode: 93.9 Hz


Optical Coupling System

Control

Electronics

Length

Reference

Laser, Optical Bench

Absolute Reference

Laser, Optical Bench

Absolute Reference

Optical Fiber

Function Box

Thermally Stabilized

Fiber Conduit


STAR mission characteristics

ESPA compatible secondary payload on an EELV launch

Circular sun-synchronous ~ 650 km orbit

Launch 2015-2016

2-year mission lifetime


Optical cavity work at Stanford

1064nm

1550nm


Vibration–insensitive optical cavities

STRAIN DISTRIBUTION

• Zero relative displacement at the ends of the optics axis

• Static Load applied at the points marked on the perimeter


• 1110 line R(56)32-0 is interesting

• Lock laser to the a10 HFS

• Sub-doppler detection

• Modulation Transfer Spectroscopy

(MTS)

• Natural Linewidth ~ 400KHz

• Broadened line < 1MHz

• Investigate narrower lines at ~516nm

Iodine MTS setup at Stanford

Arie & Byer, 1993


Iodine setup at Stanford


Motherboard, CPU, Radio

Electrical power system w/ batteries (30 W hr)

Cobolt 04-01 532nm laser

AOM x2 Circulator

Iodine cell (2cm long)

Optical bench

Spherical optical cavity

Thermal enclosure for optics

Thermal enclosures for cavity

PDH, counter boards

3U cube sat chassis

CUBESAT concept for technology testing


• nominally isotropic systems: I2, CO, C2H2 etc…

• very narrow linewidths -> excellent frequency stability

• relaxed environmental control relative to cavities

• access various LIV coefficients in fermion sector

• technical issue is making a beat note between two systems

• Femtosecond frequency combs could bridge the gap.

- But to fly a frequency comb on a satellite is still a challenge.…….

ATOMIC REFERENCES FOR KT


Lorentz Symmetry & Lorentz Violations

STAR: Search for a Lorentz violation at the level of 3×10-18 to 10-17

A factor of 100 to 300 better than ground experiments

Both orientation & velocity dependent violations

LORENTZ SYMMETRY & LORENTZ VIOLATIONS

Time dilation: equal clocks tick at different rates

Length contraction: equal rods have different lengths

Lorentz violations would exist outside of a universal preferred

reference frame, the only frame in which c is truly isotropic


Questions?

Other possibilities for violations: • Birefringence of pulsed light

• Cosmic rays

• Spectroscopy of anti-matter

• Gamma ray dispersion

• Neutrino oscillations

• Spin dependent effects……

Kostelecky, Scientific American, 2002

Documents

STAR: Space-Time Asymmetry Research Testing Lorentz ... · LVG’12 Swarthmore October 13-14, 2012 1 Shally Saraf for the Stanford STAR team October 14, 2012 STAR: Space-Time Asymmetry