star: space-time asymmetry research testing lorentz ... · lvg’12 swarthmore october 13-14, 2012...
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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
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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]
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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
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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
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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
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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
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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!
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• 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!
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• 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
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• 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
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(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?
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Peters, 2007
Crossed-cavity MM experiment
Improved MM experiment
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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?
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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
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STAR mission characteristics
ESPA compatible secondary payload on an EELV launch
Circular sun-synchronous ~ 650 km orbit
Launch 2015-2016
2-year mission lifetime
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Sun-synchronous orbital motion
of STAR instruments
Sun
Earth
Orbital Motion
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clock based on atomic transition
clock based on length standard
beat measurement
with
varying laboratory velocity
Modern KT style test configuration
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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
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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
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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
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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%
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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)
27 LVG’12 Swarthmore October 13-14, 2012 Vortrag > Autor > Dokumentname > Datum
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
28 LVG’12 Swarthmore October 13-14, 2012 Vortrag > Autor > Dokumentname > Datum
Thermal noise floor of cavities
State of the art: Iodine vs. cavity
Orbital period
STAR
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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
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Strain attenuation model - FEA
Estimated strain attenuation: > 103 per can
Extrapolating to entire enclosure: > 1015
Exceeds requirement by x1000
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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
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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
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STAR mission characteristics
ESPA compatible secondary payload on an EELV launch
Circular sun-synchronous ~ 650 km orbit
Launch 2015-2016
2-year mission lifetime
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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
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• 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
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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
40 LVG’12 Swarthmore October 13-14, 2012
• 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
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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