High Precision, Not High Energy 
Using Atomic Physics to Look Beyond the Standard Model 
Part 2: Never Measure Anything Bu...
Beyond the Standard Model 
Ways to look for new physics: 
1) Direct creation 
2) Passive detection 
Image: Mike Tarbutt/ P...
New Physics from Forbidden Events 
Parity-Violating Transitions 
 Observed, levels consistent with Standard Model 
Photon...
Frequency 
“Never measure anything but frequency!” 
-- Arthur Schawlow 
(1981 Nobel in Physics) 
Art Schawlow, ca. 1960 
h...
Clocks 
Harrison’s marine chronometer 
Image: Royal Museums Greenwich 
Newgrange passage tomb 
Built ~3000 BCE 
Timekeepin...
Comparing Clocks 
Step 1: Synchronize unknown clock with standard 
http://time.gov/
Comparing Clocks 
Step 1: Synchronize unknown clock with standard 
Step 2: Wait a while
Comparing Clocks 
Step 1: Synchronize unknown clock with standard 
Step 2: Wait a while 
Step 3: Check standard again 
Adj...
Atomic Clocks 
Δ퐸 = ℎ푓 
Atoms are ideal time standards: 
Frequency of light fixed by Quantum Mechanics 
No moving parts (n...
Ramsey Interferometry 
Norman Ramsey ca. 1952 
Image: AIP, Emilio Segre archive 
Atomic clock: 
Microwave source compared ...
Ramsey Interferometry 
Step 1: Prepare superposition state 
Light from lab oscillator used to make “p/2-pulse” 
p/2 
“Bloc...
Ramsey Interferometry 
Step 1: Prepare superposition state 
“Bloch Sphere” picture 
Step 2: Free evolution for time T 
Upp...
Ramsey Interferometry 
Step 1: Prepare superposition state 
“Bloch Sphere” picture 
Step 2: Free evolution for time T 
Ste...
Ramsey Interferometry 
Step 1: Prepare superposition state 
“Bloch Sphere” picture 
Step 2: Free evolution for time T 
Ste...
Ramsey Interferometry 
Clock signal: 
interference fringes 
Maximum probability exactly 
on resonance frequency 
Uncertain...
Fountain Clock 
Dawn Meekhof and Steve Jefferts 
with NIST-F1 (Images: NIST) 
T~1s 
Part in 1016 accuracy 
1.0000000000000...
Clocks for New Physics 
Clock technology enables 
15-digit precision 
Experimental clocks at 
17-18 digits 
Change in cloc...
Fine Structure Constant 
훼 = 
1 
4휋휖0 
푒2 
ℏ푐 
~ 
1 
137 
Enrico Fermi Image: Chicago/AIP 
Determines strength of EM force...
Electron g-Factor 
(from Hanneke et al., PRA 83 052122 (2011)) 
Best measurement of a uses 
single trapped electron 
Rotat...
Fine Structure Constant 
g = 2.00231930436146 
± 0.00000000000056 
Extract value of a from QED 
1 
훼 
= 137.035999166(34) ...
Changing Constants 
훼 = 
1 
4휋휖0 
푒2 
ℏ푐 
= 
1 
137.035999166(34) 
(Right now…) 
Limits on past change: 
Oklo “natural rea...
Astronomical Constraints 
Image: NASA 
Look at absorption/emission 
lines from distant galaxies 
Wavelength depends on 
v...
“Australian Dipole” 
From King et al., arXiv:1202.4758 [astro-ph.CO]
Modern AMO Physics 
Limits on change in a around 
Δ훼 
훼 
≤ 10−5 
Average rate of change: 
훼 
훼 
≤ 10−16 푦푟−1 
One year of ...
Clock Comparisons 
! " # " $ % & 
14 years 
6 years 
~1 year 
~1 year 
훼 
훼 
= −0.16 ± 0.23 × 10−16 푦푟−1
Clocks for New Physics 
Clock technology enables 
15-digit precision 
Experimental clocks at 
17-18 digits 
Change in cloc...
Electric Dipole Moment 
Fundamental particles have “spin” 
 Magnetic dipole moment, energy shift in magnetic field 
Elect...
Electron EDM 
Great Big Gap 
Source: B. Spaun thesis, Harvard 2014
Measuring EDM 
Basic procedure: Apply large electric field, look for change in energy 
Problem 1: Electrons are charged, m...
EDM Measurement 
Atomic 
Beam 
Source 
State 
Preparation 
State 
Detection 
Magnetic field 
Electric field
Ramsey Interference 
B E B E
EDM Limits 
Source: B. Spaun thesis, Harvard 2014 
YbF molecule 
(Imperial College) 
Thallium atom 
(Berkeley) 
ThO molecu...
Other Opportunities 
1) Systematic improvement 
Steady improvement of uncertainties in clocks, etc. 
Longer run times 
 A...
Other Opportunities 
1) Systematic improvement 
2) Similar processes, new systems 
New molecules, ions for EDM searches 
“...
Other Opportunities 
1) Systematic improvement 
2) Similar processes, new systems 
3) Exotic systems 
Measure g-factor for...
Other Opportunities 
1) Systematic improvement 
2) Similar processes, new systems 
3) Exotic systems 
4) ???? 
Never under...
Names to Conjure With 
Experiment Theory 
Toichiro Kinoshita 
Cornell University 
Gerald Gabrielse 
http://gabrielse.physi...
Clock Comparisons 
Single clock can’t detect change in a, but comparison of two atoms can 
1) Cs-Rb ground-state hyperfine...
Frequency Comb 
Ultra-fast pulsed laser: lots of little lasers with different frequencies 
Spaced by repetition rate  det...
High Precision, Not High Energy: Using Atomic Physics to Look Beyond the Standard Model (Part II)
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High Precision, Not High Energy: Using Atomic Physics to Look Beyond the Standard Model (Part II)

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Second of two lectures on using atomic physics techniques to look for exotic physics, given at the Nordita Workshop for Science Writers on Quantum Theory. This one focusses on the measuring of tiny frequency shifts using techniques developed for atomic clocks.

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High Precision, Not High Energy: Using Atomic Physics to Look Beyond the Standard Model (Part II)

  1. 1. High Precision, Not High Energy Using Atomic Physics to Look Beyond the Standard Model Part 2: Never Measure Anything But Frequency
  2. 2. Beyond the Standard Model Ways to look for new physics: 1) Direct creation 2) Passive detection Image: Mike Tarbutt/ Physics World 3) Precision measurement Look for exotic physics in relatively mundane systems using precision spectroscopy to measure extremely tiny effects
  3. 3. New Physics from Forbidden Events Parity-Violating Transitions  Observed, levels consistent with Standard Model Photon Statistics, other departures from normal  No sign, consistent with Standard Model Lorentz/ CPT symmetry violation  No sign, consistent with Standard Model  Standard Model holding strong… … but more stringent tests possible  frequency shift measurements
  4. 4. Frequency “Never measure anything but frequency!” -- Arthur Schawlow (1981 Nobel in Physics) Art Schawlow, ca. 1960 http://www.aip.org/history/exhibits/ laser/sections/whoinvented.html Extremely well-developed techniques for frequency measurements  Atomic clocks Same techniques enable ultra-precise measurements of all sorts of frequencies
  5. 5. Clocks Harrison’s marine chronometer Image: Royal Museums Greenwich Newgrange passage tomb Built ~3000 BCE Timekeeping: counting “ticks” Clock: Model compared to standard
  6. 6. Comparing Clocks Step 1: Synchronize unknown clock with standard http://time.gov/
  7. 7. Comparing Clocks Step 1: Synchronize unknown clock with standard Step 2: Wait a while
  8. 8. Comparing Clocks Step 1: Synchronize unknown clock with standard Step 2: Wait a while Step 3: Check standard again Adjust as needed…
  9. 9. Atomic Clocks Δ퐸 = ℎ푓 Atoms are ideal time standards: Frequency of light fixed by Quantum Mechanics No moving parts (not accessible by users…) All atoms of given isotope are identical SI Unit of Time (definition 1967): The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.
  10. 10. Ramsey Interferometry Norman Ramsey ca. 1952 Image: AIP, Emilio Segre archive Atomic clock: Microwave source compared to atomic transition Complicated by motion of atoms  Doppler shifts  Inhomogeneities  Limited interaction time Best frequency measurements use Ramsey Interferometry (1989 Nobel Prize in Physics)
  11. 11. Ramsey Interferometry Step 1: Prepare superposition state Light from lab oscillator used to make “p/2-pulse” p/2 “Bloch Sphere” picture
  12. 12. Ramsey Interferometry Step 1: Prepare superposition state “Bloch Sphere” picture Step 2: Free evolution for time T Upper and lower states evolve at different rates “phase” (wave frequency depends on energy of state)
  13. 13. Ramsey Interferometry Step 1: Prepare superposition state “Bloch Sphere” picture Step 2: Free evolution for time T Step 3: Second p/2-pulse, interference Final population determined by phase between states p/2
  14. 14. Ramsey Interferometry Step 1: Prepare superposition state “Bloch Sphere” picture Step 2: Free evolution for time T Step 3: Second p/2-pulse, interference Final population determined by phase between states p/2
  15. 15. Ramsey Interferometry Clock signal: interference fringes Maximum probability exactly on resonance frequency Uncertainty in frequency depends on 1/T For best performance, need to maximize free evolution time T  Cold atoms, fountain clocks Image: NIST
  16. 16. Fountain Clock Dawn Meekhof and Steve Jefferts with NIST-F1 (Images: NIST) T~1s Part in 1016 accuracy 1.0000000000000000 ±0.0000000000000001 s
  17. 17. Clocks for New Physics Clock technology enables 15-digit precision Experimental clocks at 17-18 digits Change in clock frequency due to 33-cm change in elevation (Data from Chou et al., Science 329, 1630-1633 (2010)) Sensitive to tiny shifts Lorentz violation Changing “constants” Forbidden moments General Relativity
  18. 18. Fine Structure Constant 훼 = 1 4휋휖0 푒2 ℏ푐 ~ 1 137 Enrico Fermi Image: Chicago/AIP Determines strength of EM force Energies of atomic states “Fine structure”: DEfs ~ Z2a2 “Hyperfine”: DEhfs ~ Za2 푚푒푙푒푐푡푟표푛 푚푝푟표푡표푛  Exotic physics changes a (not this much change…)
  19. 19. Electron g-Factor (from Hanneke et al., PRA 83 052122 (2011)) Best measurement of a uses single trapped electron Rotation: Δ퐸 = ℎ휈푐 Spin flip: Δ퐸 = 푔 2 ℎ휈푐 Dirac Equation predicts g=2 Difference tests QED g = 2.00231930436146 ± 0.00000000000056
  20. 20. Fine Structure Constant g = 2.00231930436146 ± 0.00000000000056 Extract value of a from QED 1 훼 = 137.035999166(34) Value from atom interferometry 1 훼 = 137.035999037(91) 8th-order Feynman diagram Comparison tests high-order QED, including muons and hadrons Extend to positrons, protons, antiprotons…
  21. 21. Changing Constants 훼 = 1 4휋휖0 푒2 ℏ푐 = 1 137.035999166(34) (Right now…) Limits on past change: Oklo “natural reactor” Image: R. Loss/Curtin Univ. of Tech. Fission products from 1.7 billion years ago Constrains possible change in a over time
  22. 22. Astronomical Constraints Image: NASA Look at absorption/emission lines from distant galaxies Wavelength depends on value of a in the past Compare many transitions, sort out redshift vs. Da
  23. 23. “Australian Dipole” From King et al., arXiv:1202.4758 [astro-ph.CO]
  24. 24. Modern AMO Physics Limits on change in a around Δ훼 훼 ≤ 10−5 Average rate of change: 훼 훼 ≤ 10−16 푦푟−1 One year of atomic clock operation Spatial variation should lead to 훼 훼 ≈ 10−19 푦푟−1 Image: NASA (Sun orbiting Milky Way moves through dipole)
  25. 25. Clock Comparisons ! " # " $ % & 14 years 6 years ~1 year ~1 year 훼 훼 = −0.16 ± 0.23 × 10−16 푦푟−1
  26. 26. Clocks for New Physics Clock technology enables 15-digit precision Experimental clocks at 17-18 digits Change in clock frequency due to 33-cm change in elevation (Data from Chou et al., Science 329, 1630-1633 (2010)) Sensitive to tiny shifts Lorentz violation Changing “constants” Forbidden moments
  27. 27. Electric Dipole Moment Fundamental particles have “spin”  Magnetic dipole moment, energy shift in magnetic field Electric dipole moment would violate T symmetry  Only tiny EDM (~10-40 e-cm) allowed in Standard Model  Larger in all Standard Model extensions
  28. 28. Electron EDM Great Big Gap Source: B. Spaun thesis, Harvard 2014
  29. 29. Measuring EDM Basic procedure: Apply large electric field, look for change in energy Problem 1: Electrons are charged, move in response to field Solution 1: Look at electrons bound to atoms or molecules Problem 2: Electrons redistribute to cancel internal field Solution 2: Relativity limits cancelation, look at heavy atoms Problem 3: Extremely large fields are difficult to produce in lab Solution 3: Polar molecules provide extremely large (GV/cm) internal fields for small applied lab fields  Look for EDM in polar molecules involving heavy atoms
  30. 30. EDM Measurement Atomic Beam Source State Preparation State Detection Magnetic field Electric field
  31. 31. Ramsey Interference B E B E
  32. 32. EDM Limits Source: B. Spaun thesis, Harvard 2014 YbF molecule (Imperial College) Thallium atom (Berkeley) ThO molecule (Harvard/Yale) de < 8.7 ×10-29 e-cm (90% c.l.)
  33. 33. Other Opportunities 1) Systematic improvement Steady improvement of uncertainties in clocks, etc. Longer run times  ACME projects another factor of 10 in EDM limit
  34. 34. Other Opportunities 1) Systematic improvement 2) Similar processes, new systems New molecules, ions for EDM searches “Nuclear clock” in thorium Dysprosium spectroscopy Lorentz symmetry tests, coupling to dark matter
  35. 35. Other Opportunities 1) Systematic improvement 2) Similar processes, new systems 3) Exotic systems Measure g-factor for positron, proton, antiproton  Test CPT symmetry Exotic “atoms” positronium, muonic hydrogen  “Proton charge radius problem”
  36. 36. Other Opportunities 1) Systematic improvement 2) Similar processes, new systems 3) Exotic systems 4) ???? Never underestimate the ingenuity of physicists… No new physics yet, but it has to be out there… Just a matter of looking carefully in the right places
  37. 37. Names to Conjure With Experiment Theory Toichiro Kinoshita Cornell University Gerald Gabrielse http://gabrielse.physics.harvard.edu/ Dave DeMille http://www.yale.edu/demillegroup/ Ed Hinds http://www3.imperial.ac.uk/ccm/ NIST Time and Frequency http://www.nist.gov/pml/div688/ ACME Collaboration http://laserstorm.harvard.edu/edm/ LNE-SYRTE http://syrte.obspm.fr/tfc/frequences_optiques/accueil_en.php
  38. 38. Clock Comparisons Single clock can’t detect change in a, but comparison of two atoms can 1) Cs-Rb ground-state hyperfine, monitored over 14 years 훼 훼 = −0.25 ± 0.26 × 10−16 푦푟−1 2) Sr optical lattice clocks, over 6 years (compare to Cs standard) 훼 훼 = −3.3 ± 3.0 × 10−16 푦푟−1 3) Al+ and Hg+ trapped ions, over 1 year 훼 훼 = −0.16 ± 0.23 × 10−16 푦푟−1
  39. 39. Frequency Comb Ultra-fast pulsed laser: lots of little lasers with different frequencies Spaced by repetition rate  determined by size of cavity Allows comparison of laser frequencies over huge range Frequency Intensity nn=n nrep+fcav ×2 nbeat = fcav n2n=2n nrep+fcav

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