Precision Measurement of the Electron’s Electric Dipole Moment Using Trapped Molecular Ions

Abstract

We describe the first precision measurement of the electron's electric dipole moment (eEDM, de) using trapped molecular ions, demonstrating the application of spin interrogation times over 700 ms to achieve high sensitivity and stringent rejection of systematic errors. Through electron spin resonance spectroscopy on 180 Hf 19 F + in its metastable 3 ∆1 electronic state, we obtain de = (0.9 ± 7.7stat ± 1.7syst) × 10 −29 e cm, resulting in an upper bound of |de| < 1.3 × 10 −28 e cm (90% confidence). Our result provides independent confirmation of the current upper bound of |de| < 9.3 × 10−29 e cm [J. Baron et al., Science 343, 269 (2014)], and offers the potential to improve on this limit in the near future.A search for a nonzero permanent electric dipole moment of the electron (eEDM, [3][4][5][6][7][8][9].The most precise eEDM measurements to date were performed using thermal beams of neutral atoms or molecules [3][4][5]. These experiments benefited from excellent statistical sensitivity provided by a high flux of neutral atoms or molecules, and decades of past work have produced a thorough understanding of their common sources of systematic error. Nonetheless, a crucial systematics check can be provided by independent measurements conducted using different physical systems and experimental techniques. Moreover, techniques that allow longer interrogation times offer significant potential for sensitivity improvements in eEDM searches and other tests of fundamental physics [10].In this Letter, we report on a precision measurement of the eEDM using molecular ions confined in a radio frequency (RF) and our use of an RF trap allow us to attain spin precession times in excess of 700 ms -nearly three orders of magnitude longer than in contemporary neutral beam experiments. This exceptionally long interrogation time allows us to obtain high eEDM sensitivity despite our lower count rate. In addition, performing an experiment on trapped particles permits the measurement of spin precession fringes at arbitrary free-evolution times, making our experiment relatively immune to systematic errors due to initial phase shifts associated with imperfectly characterized state preparation.Our apparatus and experimental sequence, shown schematically in Fig. 1, have been described in detail previously [11,12,[18][19][20][21]. We produce HfF by ablation of Hf metal into a pulsed supersonic expansion of Ar and SF 6 . The reaction of Hf with SF 6 produces HfF, which is entrained in the supersonic expansion and rovibrationally cooled through collisions with Ar. The resulting beam enters the RF trap, where HfF is ionized with pulsed UV lasers at 309.4 nm and 367.7 nm to form HfF + in its 1 Σ + , v = 0 ground vibronic state [19,20]. The ions are stopped at the center of the RF trap by a pulsed voltage on the radial trap electrodes, then confined by a DC axial electric quadrupole field and an RF radial electric quadrupole field with frequency f rf = 50 kHz. We next adiabatically turn on a spatially uniform electric bias field E rot ≈ 24 V/c...

Probing light top partners with CP violation

“…7 An additional bound on the electron EDM has been reported in ref. [32], |de| < 1.3 · 10 −28 e cm at 90% CL, which is slightly weaker than the current ACME constraint. This experiment is currently limited by statistics and in the future is expected to allow for a precision ∼ 10 −30 e cm.…”

“…As we will see, in a large class of models, the main contributions come from derivative Higgs interactions induced by the non-linear Goldstone structure. 3 The Barr-Zee effects and the Weinberg operator, in turn, give rise to sizable corrections to the electron [30][31][32], neutron [33,34] and diamagnetic atoms [35] electric dipole moments (EDM's). All these effects are tightly constrained by the present data, moreover the experimental sensitivity is expected to increase by more than one order of magnitude in the near future [32,36,37].…”

Precision Measurement of Time-Reversal Symmetry Violation with Laser-Cooled Polyatomic Molecules

“…Since both YbCCH and CaCCH can be created in a beam by reactions of the metals with HCCH [37,40], there is a promising path to creating such molecules. We can also consider molecules for ion trap experiments, where the internal comagnetometers are necessary [3] since there is no ability to reverse the applied electric field, such as LuOH þ or RaOH þ . Additionally, the combination of laser cooling, optical readout, and linear Stark shifts in small fields could be useful for quantum information processing and quantum simulation [41,42].…”

“…Since EDM sensitivity scales linearly with coherence time, trapping neutral molecules has the potential to increase sensitivity by many orders of magnitude. Trapped molecular ions have shown great power in EDM searches [3], primarily due to their long coherence time of ∼1 s. Neutral species offer the ability to increase the number of trapped molecules much more easily and essentially without limit compared to ions, while retaining strong robustness against systematic errors. Here we show that laser-cooled and trapped polyatomic molecules offer a combination of features not available in other systems, including long lifetimes, robustness against systematic errors, and scalability, and present a feasible approach to access PeV-scale BSM physics.…”

“…The molecules that have been cooled so far posses an electronic structure that makes them amenable to laser cooling, but also precludes the existence of Ω doublets, such as the 3 Δ 1 molecular state used in the two most sensitive electron EDM measurements [2,3]. These doublets enable full polarization and "internal comagnetometry," which allows for the reversal of the EDM interaction without changing any lab fields.…”