Frequency Comparison of Two High-Accuracy Al+ Optical Clocks (0911.4527v2)

Abstract: We have constructed an optical clock with a fractional frequency inaccuracy of 8.6e-18, based on quantum logic spectroscopy of an Al+ ion. A simultaneously trapped Mg+ ion serves to sympathetically laser-cool the Al+ ion and detect its quantum state. The frequency of the 1S0->3P0 clock transition is compared to that of a previously constructed Al+ optical clock with a statistical measurement uncertainty of 7.0e-18. The two clocks exhibit a relative stability of 2.8e-15/ sqrt(tau), and a fractional frequency difference of -1.8e-17, consistent with the accuracy limit of the older clock.

• The paper demonstrates a groundbreaking frequency comparison between two Al+ optical clocks using quantum logic spectroscopy to achieve unprecedented precision.
• It details the innovative use of a co-trapped Mg+ ion and a linear Paul trap to minimize systematic errors such as micromotion, secular motion, and blackbody radiation shifts.
• Results indicate a fractional frequency inaccuracy of 8.6×10⁻¹⁸ and a relative stability of 2.8×10⁻¹⁵ τ⁻¹/², paving the way for enhanced atomic timekeeping and fundamental physics research.

An Analysis of Frequency Comparison of Two High-Accuracy Al$^+$ Optical Clocks

The referenced paper discusses the construction and performance evaluation of an optical clock based on an Al$^+$ ion with significant advancements in accuracy, precision, and stability. The researchers have developed a new Al$^+$ optical clock by utilizing quantum logic spectroscopy, achieving a fractional frequency inaccuracy as low as $8.6 \times 10^{-18}$. This represents a substantial improvement in optical frequency standards, particularly when compared to the previously established cesium primary-frequency standards.

Methodological Insights

The utilization of quantum logic spectroscopy (QLS), as employed in the paper, showcases a pivotal method for addressing the limitation of detecting states in Al$^+$ ion. The experimental setup includes a sympathetically cooled Al$^+$ ion, achieved through co-trapping with a Mg$^+$ ion. This assists in the detection and cooling processes via a QLS scheme, which enables such precise measurements.

The research leverages several innovative design choices to minimize systematic errors, including a linear Paul trap constructed from all-metal electrodes and specialized laser cooling sequences that ensure minimal mass mismatch and high fidelity in quantum state transfers. These engineering techniques mitigate conventional limitations associated with motional heating in the ion trap.

Numerical Results and Stability

Significant numerical results from the paper indicate a differential fractional frequency shift of $-1.8 \times 10^{-17}$ between the newly developed clock and the previously existing Al$^+$ clock. The clocks demonstrated a relative stability of $2.8 \times 10^{-15} \tau^{-1/2}$. The stability checks highlight an impressive consistency and show the advanced technological frontiers reached by optical clock standards, capable of surpassing microwave standards by several orders of magnitude.

Systematic Evaluations

The paper offers an exhaustive analysis of various systematic shifts impacting the clock's performance, laid out concisely in Table 1 of the document. Detailed considerations of excess micromotion, secular motion, blackbody radiation shifts, and other potential shifts show that these effects, while present, are adequately corrected or held within negligible limits.

The precise calibration of excess micromotion effects and the optimization of probing laser pulses significantly contribute to achieving the stated precision levels. Quantum nondemolition transfer techniques ensure an exceptionally high fidelity of quantum state information that is pivotal for the low inaccuracy of this clock.

Implications and Future Work

The implications of this paper are multifaceted. Practically, it establishes a pathway for enhanced performance in global timekeeping systems, such as those required by GPS and telecommunications. Theoretically, the high stability and accuracy of these optical clocks present new opportunities for tests of fundamental physics, including tests of constants over time. Future comparisons with other high-precision and high-stability atomic clocks, such as NIST's Hg$^+$ optical clock, would further refine the constraints on any potential changes in fundamental constants.

In conclusion, the paper effectively demonstrates advancements in Al$^+$ optical clock technology, detailing both the engineering feats achieved and offering a comprehensive understanding of the systematic effects and numerical achievements of the clock comparison paper. This work embodies a substantial step forward in the field of high-precision frequency metrology, paving the way for future innovations in atomic timekeeping and fundamental physics inquiries.