Cornell Group - EDM with ThF+ (Gen III)

Selfie of Cornell lab members at the Denver Botanic Gardens. May 4, 2026.

Denver Botanic Gardens - May 4, 2026.

Back row (left to right): Michail Athanasakis-Kaklamanakis, Anzhou Wang, Eric Cornell, Patricia Hector-Hernandez. Front row (left to right): Tuan Anh Nguyen, Sun Yool Park.

Additional group members: Jun Ye (co-advisor), Rohan Kompella (undergraduate).

Goal

To have the most precise measurement of the eEDM (de), or to place an even more stringent bound on de than our experiment using HfF+, i.e., we want to have a very small uncertainty in the measurement, 未诲e.

Figure of merit

The quality of our precision metrology of the eEDM goes as

未诲e ~ 1 / (Eeff蟿(Nsingle路frep路Tint)1/2 )

where

  1. Eeff is the effective electric field that the electron sees within the molecule;
  2. 蟿 is the coherence time of the eEDM-sensitive quantum state that we are probing;
  3. Nsingle is the number of ions that we detect per measurement (our measurement is a destructive process);
  4. frep is the repetition rate of our experiment; and
  5. Tint is the total integration time of our measurement (or the total amount of time that the graduate students are willing to take data).

In other words, we want (in order corresponding to the above):

  1. The best molecular ion: ThF+! ThF+ has a 50% larger effective electric field than HfF+ used in our ongoing experiment.
  2. The best molecular ion: ThF+! The eEDM-sensitive state in ThF+ is the ground state, which means that it is not limited to natural decay lifetimes.
  3. A big ion trap: to trap more ions!
  4. A multiplexed ion trap: the Bucket Brigade! The Bucket Brigade is a conveyor belt of ion traps, i.e., a brigade of buckets containing ions. This allows us to 鈥渕ultithread鈥 our experiment and have a repetition rate that is not limited to how long it takes to perform one shot of the experiment.
  5. Hardworking and motivated graduate students! The eEDM experiment requires us to be a jack of all trades (and master of some). Technologies that we use include: (i) high power lasers, (ii) ultra high vacuum systems, (iii) high voltage electronics, (iv) simulations, (v) ion optics, (vi) cryogenics, and many more!
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Bucket Brigade (the Baby Bucket)

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Current Status

In the past few years, we wrapped up spectroscopy on ThF+ (and ThF) and assembled a prototype Bucket Brigade: the Baby Bucket Brigade! With our prototype, we have demonstrated:

  • Efficient simultaneous detection of states oppositely oriented with respect to a polarizing electric field
  • Suppression of population loss due to blackbody radiation, with up to few-minute lifetimes achieved at liquid-nitrogen temperatures
  • Long coherence, surpassing that of the Gen. II HfF+ experiment
  • Preservation of coherence while transporting ions along the bucket brigade
  • An rf quantum control approach that enables multiplexing our measurement protocol

As a final experiment with Baby Bucket, we will demonstrate the proof-of-principle multiplexed measurement scheme by sequentially loading and preparing multiple packets of ions such that new packets don鈥檛 disturb previously loaded ones. We are also designing and will soon be assembling a final version of the Bucket Brigade鈥攊ncorporating lessons learned from Baby Bucket鈥攖o surpass the current best limit on the eEDM.

Check out our selected papers below, and drop an email to learn more!

Selected Paper Abstracts

Asymmetrical distribution of dissociation photofragments for three different |Ω|=2 intermediate states.

High-efficiency quantum-state detection of ThF+ with resonance-enhanced multiphoton asymmetric dissociation

Efficient quantum-state detection is crucial for many precision control experiments, such as the ongoing effort to probe the electron's electric dipole moment using trapped molecular 232ThF+ ions at JILA. While quantum-state detection through state-selective photodissociation has been successfully implemented on this molecule, progress has been hindered by low dissociation efficiency. In this work, we perform spectroscopy on the molecule to identify excited states that facilitate more efficient photodissociation. For the most favorable transition, we achieve a dissociation efficiency of 57(14)% with quantum-state selectivity. Additionally, we discuss several state detection protocols that leverage favorable excited states that will facilitate simultaneous readout of all EDM relevant states, allowing further improvement of overall statistics.

Phys. Rev. A 112, 053104 (2025)

Systematic and statistical uncertainty evaluation of the HfF+ electron electric dipole moment experiment

Systematic and statistical uncertainty evaluation of the听HfF+听electron electric dipole moment experiment

We have completed a new precision measurement of the electron's electric dipole moment using trapped HfF+听in rotating bias fields. We report on the accuracy evaluation of this measurement, describing the mechanisms behind our systematic shifts. Our systematic uncertainty is reduced by a factor of 30 compared to the first generation of this measurement. Our combined statistical and systematic accuracy is improved by a factor of 2 relative to any previous measurement.

Phys. Rev. A听108, 012804听(2023)

Spectroscopy on the eEDM-sensitive states of ThF+

Spectroscopy on the eEDM-sensitive states of ThF+

An excellent candidate molecule for the measurement of the electron鈥檚 electric dipole moment (eEDM) is thorium monofluoride (ThF+) because the eEDM-sensitive state, 3鈭1, is the electronic ground state, and thus is immune to decoherence from spontaneous decay. We perform spectroscopy on X 3鈭1 to extract three spectroscopic constants crucial to the eEDM experiment: the hyperfine coupling constant, the molecular frame electric dipole moment, and the magnetic g-factor. To understand the impact of thermal blackbody radiation on the vibrational ground state, we study the lifetime of the first excited vibrational manifold of X 3鈭1. We perform ab initio calculations, compare them to our results, and discuss prospects for using ThF+ in a new eEDM experiment at JILA.

Phys. Rev. A. 105, 022823 (2022)

Second-scale coherence measured at the projection noise limit with hundreds of molecular ions

Second-scale coherence measured at the projection noise limit with hundreds of molecular ions

Cold molecules provide a platform for a variety of scientific applications such as quantum computation, simulation, cold chemistry, and searches for physics beyond the Standard Model. Mastering quantum state control and measurement of diverse molecular species is critical for enabling these applications. However, state control and readout are difficult for the majority of molecular species due to the lack of optical cycling transitions. Here we demonstrate internal state cooling and orientation-selective photofragment imaging in a spin precession measurement with multi-second coherence, allowing us to achieve the quantum projection noise (QPN) limit in a large ensemble of trapped molecular ions. We realize this scheme for both HfF+ and ThF+ --- molecules chosen for their sensitivity to beyond Standard Model physics rather than their amenability to state control and readout.

Phys. Rev. Lett. 124, 053201 (2020)

Visible and Ultraviolet Laser Spectroscopy of ThF

Visible and Ultraviolet Laser Spectroscopy of ThF

The molecular ion ThF+ is the species to be used in the next generation of search for the electron's Electric Dipole Moment (eEDM) at JILA. The measurement requires creating molecular ions in the eEDM sensitive state, the rovibronic ground state 3螖1, v+=0, J+=1. Survey spectroscopy of neutral ThF is required to identify an appropriate intermediate state for a Resonance Enhanced Multi-Photon Ionization (REMPI) scheme that will create ions in the required state. We perform broadband survey spectroscopy (from 13000 to 44000 cm-1) of ThF using both Laser Induced Fluorescence (LIF) and 1+1' REMPI spectroscopy. We observe and assign 345 previously unreported vibronic bands of ThF. We demonstrate 30% efficiency in the production of ThF+ ions in the eEDM sensitive state using the 惟 = 3/2 [32.85] intermediate state. In addition, we propose a method to increase the aforementioned efficiency to ~100% by using vibrational autoionization via core-nonpenetrating Rydberg states, and discuss theoretical and experimental challenges. Finally, we also report 83 vibronic bands of an impurity species, ThO.

J. Mol. Spec. 358, (2019) 1-16

Broadband velocity modulation spectroscopy of ThF+ for use in a measurement of the electron electric dipole moment

Broadband velocity modulation spectroscopy of ThF+ for use in a measurement of the electron electric dipole moment

A number of extensions to the Standard Model of particle physics predict a permanent electric dipole moment of the electron (eEDM) in the range of the current experimental limits. Trapped ThF+ will be used in a forthcoming generation of the JILA eEDM experiment. Here, we present extensive survey spectroscopy of ThF+ in the 700-1000 nm spectral region, with the 700-900 nm range fully covered using frequency comb velocity modulation spectroscopy. We have determined that the ThF+ electronic ground state is X 3螖1, which is the eEDM-sensitive state. In addition, we report high-precision rotational and vibrational constants for 14 ThF+ electronic states, including excited states that can be used to transfer and readout population in the eEDM experiment.

J. Mol. Spec. 319, (2016) 1-9