[Paper Review] Demonstration of an Electron Electric Dipole Moment Experiment Using Electric-Field Quantization in a Cesium Cold Atom Fountain

Jason Amini, Charles T. Munger+1 more|arXiv (Cornell University)|Feb 1, 2006

Atomic and Subatomic Physics Research47 references32 citations

TL;DR

This paper demonstrates a cesium cold atom fountain experiment using electric-field quantization to suppress motional magnetic field systematics, achieving a projected sensitivity of 2×10⁻⁵⁰ C·m (1.3×10⁻²⁹ e·cm) for the electron electric dipole moment (e-EDM). The method leverages fountain geometry and field-free state preparation to minimize systematic errors, with a measured EDM of −0.7±2.2×10⁻⁴³ C·m in the demonstration, validating the approach for future high-sensitivity searches.

ABSTRACT

A Cs fountain electron electric dipole moment (EDM) experiment using electric-field quantization is demonstrated. With magnetic fields reduced to 200 pT or less, the electric field lifts the degeneracy between hyperfine levels of different|mF| and, along with the slow beam and fountain geometry, suppresses systematics from motional magnetic fields. Transitions are induced and the atoms polarized and analyzed in field-free regions. The feasibility of reaching a sensitivity to an electron EDM of 2 x 10 exp(-50) C-m [1.3 x 10 exp(-29) e-cm] in a cesium fountain experiment is discussed.

Motivation & Objective

• To develop a high-sensitivity electron electric dipole moment (e-EDM) experiment using cold cesium atoms in a fountain setup.
• To suppress systematic errors from motional magnetic fields, which can mimic an e-EDM signal.
• To demonstrate the feasibility of electric-field quantization as a method to eliminate leading-order motional magnetic field effects.
• To achieve a projected e-EDM sensitivity of 2×10⁻⁵⁰ C·m, two orders of magnitude below current limits.
• To validate the use of field-free state preparation and analysis for reducing systematic biases.

Proposed method

• Electric-field quantization is employed, where the electric field E lifts the degeneracy of hyperfine sublevels |mF|, eliminating the need for a static magnetic field to define quantization axis.
• The fountain geometry enables atom-by-atom cancellation of velocity-induced magnetic fields (Bmot = v×E/c²) via upward and downward atomic motion.
• Residual magnetic fields (≤200 pT) are actively nullified using magnetic shielding and feedback-controlled nulling coils to minimize B⊥res.
• State preparation and analysis are performed in field-free regions (B ≤200 pT, E = 0), using optical pumping and state-selective fluorescence detection with a single diode laser.
• Transitions between mF states are induced via pulsed magnetic fields (B∥ and By), with resonance frequency shifts analyzed as a function of electric field reversal.
• Systematic errors are estimated using the energy shift equation W(mF)/h = ǫE²m²F + gµB||mF + K₁(gµ)²B⊥²/(ǫE²) − K₂(gµ)³B⊥²B||/(ǫE²)² − deRmFE/(4h), where de is the e-EDM.

Experimental results

Research questions

• RQ1 Can electric-field quantization effectively suppress motional magnetic field systematics in a cesium fountain e-EDM experiment?
• RQ2 What level of magnetic field control is required to achieve sub-10⁻⁵⁰ C·m sensitivity in e-EDM measurements?
• RQ3 How does the use of field-free state preparation and analysis reduce systematic errors compared to conventional magnetic field quantization?
• RQ4 What is the achievable sensitivity of the e-EDM experiment using a seven-quanta transition (mF = ±4 ↔ ∓3)?
• RQ5 Can electrostatic lenses and heated glass electrodes improve atomic flux and field stability for high-sensitivity e-EDM detection?

Key findings

• The demonstration experiment achieved an e-EDM measurement of −0.7±2.2×10⁻⁴³ C·m (−0.5±1.4×10⁻²² e·cm) at 1σ statistical uncertainty, validating the method.
• The estimated motional systematic error in the demonstration was 3×10⁻⁴⁵ C·m (2×10⁻²⁴ e·cm), which is negligible compared to the projected sensitivity.
• With improved magnetic shielding (20 pT), lower velocity (<3 mm/s), and E = 13.5 MV/m, the systematic error would be reduced to 1.2×10⁻⁵¹ C·m (7×10⁻³¹ e·cm), far below the current experimental limit.
• A sensitivity of 2×10⁻⁵⁰ C·m (1.3×10⁻²⁹ e·cm) is feasible using a 13.5 MV/m electric field and a seven-quanta transition, requiring ~225 hours of integration time for statistical precision.
• Electrostatic lens triplets can compensate for defocusing at electric field plate entrances, enabling nearly 100% atomic return and high flux (>1×10⁹ atoms/s) for future experiments.
• Heated glass electrodes can reduce Johnson noise and enable stable operation at high electric fields (≥13.5 MV/m).