High Precision, Not High EnergyUsing Atomic Physics to Look Beyond the Standard Model

Part 2: Never Measure Anything But Frequency

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

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

Frequency

“Never measure anything but frequency!”-- Arthur Schawlow (1981 Nobel in Physics)

http://www.aip.org/history/exhibits/laser/sections/whoinvented.html

Art Schawlow, ca. 1960

Extremely well-developed techniques for frequency measurements

Atomic clocks

Same techniques enable ultra-precise measurements of all sorts of frequencies

Clocks

Harrison’s marine chronometerImage: Royal Museums Greenwich

Newgrange passage tomb Built ~3000 BCE

Timekeeping: counting “ticks”

Clock: Model compared to standard

Comparing ClocksStep 1: Synchronize unknown clock with standard

http://time.gov/

Comparing ClocksStep 1: Synchronize unknown clock with standard

Step 2: Wait a while

Comparing ClocksStep 1: Synchronize unknown clock with standard

Step 2: Wait a while

Step 3: Check standard again

Adjust as needed…

Atomic Clocks

Δ 𝐸=h𝑓Atoms 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.

Ramsey Interferometry

Norman Ramsey ca. 1952Image: 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)

Ramsey Interferometry

Step 1: Prepare superposition state

Light from lab oscillator used to make “p/2-pulse”

p/2“Bloch Sphere” picture

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)

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

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

Ramsey InterferometryClock 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

Fountain Clock

Dawn Meekhof and Steve Jefferts with NIST-F1 (Images: NIST)

T~1s

Part in 1016 accuracy

1.0000000000000000 ±0.0000000000000001 s

Clocks for New PhysicsClock technology enables 15-digit precision

Experimental clocks at 17-18 digits

Change in clock frequency due to33-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

Fine Structure Constant

𝛼= 14 𝜋𝜖0

𝑒2

ℏ𝑐1

137

Enrico Fermi Image: Chicago/AIP

Determines strength of EM force

Energies of atomic states

“Fine structure”: DEfs ~ Z2a2

“Hyperfine”: DEhfs ~ Za2

Exotic physics changes a

(not this much change…)

Electron g-Factor

g = 2.00231930436146 ± 0.00000000000056

(from Hanneke et al., PRA 83 052122 (2011))

Best measurement of a uses single trapped electron

Rotation:

Δ 𝐸=h𝜈𝑐

Spin flip:

Δ 𝐸=𝑔2

h𝜈𝑐

Dirac Equation predicts g=2 Difference tests QED

Fine Structure Constantg = 2.00231930436146 ± 0.00000000000056

Extract value of a from QED

1𝛼

=137.035999166 (34)

1𝛼

=137.035999037 (91)

Value from atom interferometry

Comparison tests high-order QED, including muons and hadrons

8th-order Feynmandiagram

Extend to positrons, protons, antiprotons…

Changing Constants

𝛼= 14 𝜋𝜖0

𝑒2

ℏ𝑐= 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

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

“Australian Dipole”

From King et al., arXiv:1202.4758 [astro-ph.CO]

Modern AMO Physics

Limits on change in a around

Δ𝛼𝛼

≤ 10− 5

Average rate of change:�̇�𝛼

≤ 10−16 𝑦 𝑟−1

One year of atomic clock operation

Spatial variation should lead to

�̇�𝛼

≈ 10−19 𝑦 𝑟−1

Image: NASA

(Sun orbiting Milky Way moves through dipole)

Clock Comparisons

! " # " $ % &

14 years

6 years

~1 year

~1 year

�̇�𝛼

=(− 0.16 ± 0.23 )×10−16 𝑦 𝑟−1

Clocks for New PhysicsClock technology enables 15-digit precision

Experimental clocks at 17-18 digits

Change in clock frequency due to33-cm change in elevation(Data from Chou et al., Science 329, 1630-1633 (2010))

Sensitive to tiny shifts

Lorentz violation

Changing “constants”

Forbidden moments

Electric Dipole MomentFundamental 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

Electron EDM

Source: B. Spaun thesis, Harvard 2014

Great Big Gap

Measuring EDMBasic 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

EDM Measurement

AtomicBeamSource

StatePreparation StateDetection

Magnetic fieldElectric field

Ramsey Interference

B E B E

EDM Limits

Source: B. Spaun thesis, Harvard 2014

Thallium atom(Berkeley)

YbF molecule(Imperial College)

ThO molecule(Harvard/Yale)

de < 8.7 ×10-29 e-cm (90% c.l.)

Other Opportunities

1) Systematic improvement

Steady improvement of uncertainties in clocks, etc.

Longer run times

ACME projects another factor of 10 in EDM limit

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

Other Opportunities

1) Systematic improvement

2) Similar processes, new systems

Measure g-factor for positron, proton, antiproton

Test CPT symmetry

Exotic “atoms” positronium, muonic hydrogen

“Proton charge radius problem”

3) Exotic systems

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

Names to Conjure With

Experiment Theory

Toichiro Kinoshita Cornell University

Gerald Gabrielsehttp://gabrielse.physics.harvard.edu/

Dave DeMillehttp://www.yale.edu/demillegroup/

Ed Hindshttp://www3.imperial.ac.uk/ccm/

NIST Time and Frequencyhttp://www.nist.gov/pml/div688/

LNE-SYRTE http://syrte.obspm.fr/tfc/frequences_optiques/accueil_en.php

ACME Collaborationhttp://laserstorm.harvard.edu/edm/

Clock ComparisonsSingle clock can’t detect change in a, but comparison of two atoms can

1) Cs-Rb ground-state hyperfine, monitored over 14 years

�̇�𝛼

=(− 0.25 ± 0.26 )×10−16 𝑦 𝑟−1

2) Sr optical lattice clocks, over 6 years (compare to Cs standard)

�̇�𝛼

=(− 3.3 ± 3.0 ) ×10− 16 𝑦𝑟 −1

3) Al+ and Hg+ trapped ions, over 1 year

�̇�𝛼

=(− 0.16 ± 0.23 )×10−16 𝑦 𝑟−1

Frequency Comb

Frequency

Intensity

nn=n nrep+fcav ×2

nbeat = fcav

n2n=2n nrep+fcav

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