Quadruply Ionized Barium as a Candidate for a High-Accuracy Optical Clock.

Area of Science:

• Atomic Physics
• Quantum Optics
• Metrology

Background:

• Optical atomic clocks are crucial for fundamental physics tests and timekeeping.
• Developing new atomic systems with enhanced stability and reduced systematic uncertainties is an ongoing challenge.

Purpose of the Study:

• To identify and evaluate Ba^{4+} (Te-like) as a potential candidate for a high-accuracy optical clock.
• To investigate the feasibility of using the ^{3}P_{J} fine structure manifold for clock transitions.

Main Methods:

• Relativistic many-body calculations were performed to determine the properties of Ba^{4+}.
• The electric quadrupole transition between the ground (3P2) and first-excited (3P0) states at 338.8 THz was analyzed.

Main Results:

• Ba^{4+} exhibits an anomalous, nonmonotonic energy ordering within its ^{3}P_{J} fine structure manifold.
• The excited clock state has a lifetime of several seconds, enabling low statistical uncertainty.
• The ion shows small, negative differential static scalar polarizability, reducing sensitivity to blackbody radiation and allowing for Stark and micromotion shift cancellation.

Conclusions:

• Ba^{4+} is a highly promising candidate for next-generation optical clocks.
• Its properties offer advantages in suppressing systematic errors compared to many existing optical clock systems.
• The ion's sensitivity to fine-structure constant variation is notable, providing opportunities for fundamental physics research.