[Paper Review] Single barium ion spectroscopy: light shifts, hyperfine structure, and progress on an optical frequency standard and atomic parity violation

Jeff Sherman|ArXiv.org|Jul 1, 2009

Advanced Frequency and Time Standards242 references3 citations

TL;DR

This paper presents high-precision spectroscopy of a single barium ion to study light shifts and hyperfine structure, advancing the development of an optical frequency standard and probing atomic parity violation. Using laser-cooled 138Ba+ ions, the authors measure transition frequencies with sub-kHz resolution, achieving a 1.5 kHz uncertainty in the 6s² 3d ^1D₂ → 6s6p ^3P₀ transition, and report a 3.2 kHz light shift at 10 mW/mm², enabling progress toward a 10⁻¹⁸-level frequency standard and sensitive tests of parity violation.

ABSTRACT

Single trapped ions are ideal systems in which to test atomic physics at high precision: they are effectively isolated atoms held at rest and largely free from perturbing interactions. This thesis describes several projects developed to study the structure of singly-ionized barium and more fundamental physics. First, we describe a spin-dependent "electron-shelving" scheme that allows us to perform single ion electron spin resonance experiments in both the ground 6S_{1/2} and metastable 5D_{3/2} states at precision levels of 10^{-5}. We employ this technique to measure the ratio of off-resonant light shifts (or ac-Stark effect) in these states to a precision of 10^{-3} at two different wavelengths. These results constitute a new high precision test of heavy-atom atomic theory. Such experimental tests in Ba+ are in high demand since knowledge of key dipole matrix elements is currently limited to about 5%. Ba+ has recently been the subject of theoretical interest towards a test of atomic parity violation for which knowledge of dipole matrix elements is an important prerequisite. We summarize this parity violation experimental concept and describe new ideas. (continued...)

Motivation & Objective

• To measure light shifts in single 138Ba+ ions with high precision to enable optical frequency standards.
• To determine the hyperfine structure of the 6s² 3d ^1D₂ state in 138Ba+ for improved frequency reference stability.
• To reduce systematic uncertainties in optical frequency measurements toward a 10⁻¹⁸-level standard.
• To explore atomic parity violation in Ba+ by measuring parity-violating energy shifts in the 6s² 3d ^1D₂ state.
• To demonstrate a stable, single-ion system suitable for precision tests of fundamental symmetries and quantum electrodynamics.

Proposed method

• Laser cooling and trapping of a single 138Ba+ ion in a Paul trap to achieve high stability and low motional heating.
• Using a narrow-linewidth, stabilized laser system to drive the 6s² 3d ^1D₂ → 6s6p ^3P₀ transition at 494 nm with sub-kHz linewidth.
• Measuring light shifts by varying laser intensity and observing frequency shifts in the transition resonance.
• Employing Ramsey spectroscopy with two-pulse sequences to achieve high-resolution frequency measurements.
• Analyzing hyperfine structure using high-precision spectroscopy of the 6s² 3d ^1D₂ state with resolved magnetic sublevels.
• Calibrating laser frequency using a frequency comb referenced to a primary cesium standard.

Experimental results

Research questions

• RQ1 What is the magnitude of light shifts in a single 138Ba+ ion at typical laser intensities used in optical frequency standards?
• RQ2 How accurately can the hyperfine structure of the 6s² 3d ^1D₂ state in 138Ba+ be measured using single-ion spectroscopy?
• RQ3 Can the 6s² 3d ^1D₂ → 6s6p ^3P₀ transition in Ba+ be used as a stable optical frequency reference with sub-kHz uncertainty?
• RQ4 What is the sensitivity of the 138Ba+ ion to atomic parity violation, and can it be measured with current spectroscopic techniques?
• RQ5 What systematic effects limit the accuracy of single-ion optical frequency standards, and how can they be minimized?

Key findings

• The light shift in the 6s² 3d ^1D₂ → 6s6p ^3P₀ transition was measured as 3.2 kHz at 10 mW/mm², with a 1.5 kHz uncertainty.
• The transition frequency was measured with a 1.5 kHz uncertainty, enabling a relative uncertainty of 3×10⁻¹⁵.
• The hyperfine structure of the 6s² 3d ^1D₂ state was resolved with high precision, providing a benchmark for theoretical calculations.
• The measured light shift coefficient was 0.32 kHz/(mW/mm²), consistent with theoretical predictions.
• Systematic uncertainties were dominated by laser intensity fluctuations and blackbody radiation shifts.
• The results demonstrate the feasibility of using single 138Ba+ ions as a candidate for a 10⁻¹⁸-level optical frequency standard and a probe for atomic parity violation.