Precision Measurements with Polyatomic Molecules Nick Hutzler - PowerPoint PPT Presentation

Precision Measurements with Polyatomic Molecules Nick Hutzler Caltech

Internal Fields ▪ Thanks Naftali, Alexander for EDM introduction and motivation! ▪ Atoms/molecules have extremely large fields ▪ Relativistic ~Z 2-3 enhancement ▪ Up to 10 6 enhancement over lab fields ▪ CPV moments induce CPV energy shifts in the atom/molecule |↓  |↑  2

Polarization ▪ Problem – constituents experiences zero average field! ▪ Atom/molecule states always have this symmetry in free space ▪ Solution: polarize ▪ Apply lab field to orient atom/molecule ▪ Interaction no longer averages to zero ▪ Sensitivity  polarization P ▪ Requires mixing opposite parity states, ε > d/ Δ 3

Atoms vs. molecules ▪ Atoms Atoms ▪  ~ 100 THz (electronic)  ~ 100 THz ▪ P ~ 10 -3 @ 100 kV/cm ▪ Molecules ▪  ~ 10 GHz (rotational) ▪ P ~ O (1) @ 10 kV/cm ▪ “Molecules are 1000x Molecules more sensitive”  ~ 10 GHz ▪ Some molecules have parity doublets ,  <10 MHz Parity ▪ Enables full polarization in J + J Doubling small fields… and more ! J –  ~ 10 MHz 4

Molecule State of the Art: ACME ▪ Harvard, Yale, Northwestern ▪ Molecular beam spin precession in ThO ▪ Current best limit on the electron EDM ▪ |d e | < 1.1 x 10 -29 e cm ▪ Statistics limited ▪ ~100x eEDM improvement in past since 2006 National Academies report! ▪ Already probing the TeV scale – beyond the LHC ▪ ~3-30 TeV for 1 or 2 loop couplings to new CPV physics ▪ Molecules are worth it! ▪ Not just more sensitive, but ACME Collaboration, Nature 562 , 355 (2018) www.electronedm.info more robust 5

Spin precession Time  B E  = 0  + =  B  + dE  H = − d  E −  B Time  B E  - =  B  − dE    dE  6

Nothing is perfect… Time  B E  = 0  + =  B  + dE  + ??? H = − d  E −  B Time  B E  - =  B  − dE  +??? dE /  B < 10 -6   dE  + ??? 7

Internal Comagnetometers ▪ Parity doublets enable full polarization and “internal + comagnetometer states” ▪ A.k.a. “spectroscopic reversal” ▪ Huge advantages! − ▪ Smaller fields ▪ EDM sensitivity saturated, independent of field ▪ Measure without field reversals − ▪ Systematics amplified in other channels ▪ Enables ion trap measurements (JILA method) + ▪ Just as important as sensitivity increase (in my opinion) 8

Smaller Fields, Saturation ▪ Polarization requires ~1,000x smaller fields ▪ Simpler engineering, enhanced quality of life ▪ Directly suppresses geometric phases, motional fields, leakage currents, etc. ▪ (These are serious! n, Tl, …) ▪ Also suppresses many systematics for optically trapped species ▪ Polarization can be saturated ▪ EDM no longer depends on E field, most systematics would 9

Spectroscopic Reversal ▪ Traditionally, need to reverse E fields to isolate + EDM vs. everything else ▪ With parity doublets, can reverse EDM signal by using − different molecular states ▪ Perform measurement in two “flipped” molecular states − ▪ Cancels field-related systematics with high fidelity ▪ Can (and do) still reverse fields as a check + ▪ Systematics amplified in field flipped channel 10

Internal Comagnetometers ▪ Example from ACME I : EDM Asymmetry Purposeful E-correlated B With molecule flip field of ~1 mG (!) ▪ Error ~ 10 -27 e cm/mG ▪ Error shows up in “field flip only” channel (ignoring spectroscopic reversal) >100x larger EDM Asymmetry Without molecule flip ▪ Proof of systematic error suppression ▪ Resource for hunting systematics 11

Internal Comagnetometers ▪ These techniques have been critical for the most + sensitive eEDM searches ▪ JILA needs spectroscopic reversal since can’t flip E field − in an ion trap ▪ Both ACME and JILA rely on them for systematic − robustness ▪ Parity doublets are great! Let’s use them for everything! + 12

Parity Doublets ▪ Don’t exist in atoms (in the + sense that I mean…) J – ▪ In diatomics, we have Λ (or Ω) doubling ▪ Projections of L elec along internuclear axis are nearly Rotation degenerate ▪ Split by Coriolis-type L elec interactions with rotation ▪ Similar in nuclei! ▪ Requires electronic orbital angular momentum +𝚳 −𝚳 ▪ Rules out lots of interesting species! 13

Polyatomic molecules ▪ Polyatomic molecules generically have parity doublets ▪ Effectively independent of electronic structure, atom choice ▪ Comparable complexity to diatomics (discussed here…) ▪ Only way to access parity doublets for many exciting species ▪ Ba, Ra, Yb , Hg, Tl, … ▪ Generically opens up many options for exotic species ▪ Only way to combine CPV sensitivity, parity doublets, and ultracold techniques I. Kozyryev and NRH, Phys. Rev. Lett. 119 , 133002 (2017) 14

ℓ -doublets ▪ Example: linear triatomic ▪ MOH, MCCH, … ▪ Three mechanical modes ▪ Bending mode is doubly degenerate ▪ Eigenstates have orbital angular Bend momentum ℓ Symmetric Asymmetric stretch stretch ▪ Coupling of ℓ to rotation creates ℓ parity doublet ▪ Typically ~ 10 MHz ▪ Independent of electronic structure! ▪ Symmetric tops – rotations about symmetry axis ℓ ▪ Splittings even smaller ▪ MCH 3 , MOCH 3 , … ▪ Doesn’t interfere with laser cooling 15

Where we are going… ▪ 10 6 molecules ▪ 10 s coherence ▪ Large enhancement(s) M new phys ~ 1,000 TeV (!) ▪ Robust error rejection Beyond the reach of ▪ Efficient control/readout conceivable accelerators ▪ 1 week averaging Even before implementing truly advanced quantum techniques, such as squeezing, interaction engineering, … So… how to build this? 16 Figure adapted from A. J. Daley, Nature 501 , 497 (2013)

Quantum Control with Atoms D. Barredo et al ., Nature 561 , 79 – 82 (2018) T. G. Tiecke, et al. , Nature 508 , 241 (2014). A. Mazurenko et al. , Nature 545, 462-466 (2017) 17

Quantum Control with Molecules? Many people are working on this, with many recent and exciting results! Precision measurements, quantum chemistry, many- body, information, … 18

Laser cooling/trapping ▪ Quantum control requires Yb Atoms ultracold temperatures ▪ Lasers can be used to cool and trap < mK gases ▪ Forces, including dissipative, from photon scattering momentum kicks ▪ Important driver of many quantum techniques ▪ Critical part of Ra EDM! ▪ Claim: only (proven) suitable method for us 19

Laser cooling molecules Excited ▪ Requires many (~10 5 ) cycles “Atoms” of absorption, spontaneous decay Excitation Laser Decay ▪ Decay to other states stops the cooling process Other ▪ Internal vibrational, Ground rotational levels are excited in decay Excited ▪ For carefully chosen “Molecules” molecules, this is manageable ▪ Most of the leaders and pioneers in this area are in the room! Ground Rotation, vibration, … 20

Laser cooling molecules Excited ▪ Requires many (~10 5 ) cycles “Atoms” of absorption, spontaneous decay Excitation Laser Decay ▪ Decay to other states stops the cooling process Other ▪ Internal vibrational, Ground rotational levels are excited in decay Excited ▪ For carefully chosen “Molecules” molecules, this is manageable ▪ Laser cooled and trapped molecules now exist! ▪ SrF (DeMille, 2014) Ground Rotation, vibration, … ▪ CaF (Tarbutt 2017, Doyle 2017) ▪ YO (Ye, 2018) 21

Electronic Structure for Laser Cooling ▪ Generally works for molecules with metal- centered s orbital(s) ▪ Alkaline-earth (s 2 ) ▪ Single bond to halogen (F) ▪ Orbital hybridization pushes electron away from chemical bond ▪ Decouples electronic, molecular excitations ▪ Works for many bonding partners – polyatomics!* ▪ Laser cooling comes from metal centered electron ▪ Shown with SrOH (Doyle, 2017) M. D. Di Rosa, Eur. Phys. J. D 31 , 395 (2004), A. M. Ellis, Int. Rev. Phys. Chem. 20 , 551 (2001) 22 *T. A. Isaev and R. Berger, PRL 116 , 63006 (2016), *I. Kozyryev, et al., ChemPhysChem 17 , 3641 (2016)

Laser Coolable Molecules for Precision Measurement of CP Violation ▪ CPV sensitivity also comes from electronic structure ▪ Core-penetrating s electrons ▪ Several laser-coolable options, including at this workshop! ▪ BaF, HgF, RaF, TlF YbF , … ▪ Polyatomic analogues have similar sensitivity ▪ CPV comes from metal center ▪ Explicitly shown for BaOH, RaOH, RaOH + , ThOH + , TlCN, Core-penetrating YbOH (so far) orbitals → good ▪ Why polyatomics? CPV sensitivity ▪ Access to parity doublets! ▪ MF → MOH, MOCH 3 , … 23

Incompatible Features Internal Comagnetometers Laser Cooling ▪ ThO, WC, TaN, HfF + , … ▪ YbF, BaF, RaF, TlF , … ▪ “Requires” L elec > 0 ▪ “Requires” L elec = 0 ▪ Interferes with laser cooling ▪ No internal comagnetometers ▪ Similar story for assembled molecules (HgLi, YbCs , …) 24

Incompatible Features Internal Comagnetometers Laser Cooling ▪ ThO, WC, TaN, HfF + , … ▪ YbF, BaF, RaF, TlF , … ▪ “Requires” L elec > 0 ▪ “Requires” L elec = 0 ▪ Interferes with laser cooling ▪ No internal comagnetometers ▪ Similar story for assembled Only in diatomics! molecules (HgLi, YbCs , …) 25