Preliminary Frequency Comparison of Two ⁴⁰ Ca ⁺ Optical Frequency Standards

Abstract

Frequency comparison is one of the most efficient ways to evaluate the performance of a frequency standard. Based on the pre-existing 40 Ca + optical frequency standard, we set up the second 40 Ca + optical frequency standard, which has been improved in the materials and structure of ion traps for better control of the magnetic field. After the compensation, the residual magnetic field at the position of the ion is adjusted to be ∼500 nT with a long time jitter of ∼10 nT, which is better than the pre-existing 40 Ca + optical frequency standard. We realize the '4-point-closed-loop locking' on the second 40 Ca + optical frequency standard after a series of preparatory works. Through half an hour of measurement time, the two frequency standards exhibited a stability of 2.1 × 10 −13 𝜏 −1/2 and a relative frequency difference of 1.5 (2.9) Hz.

Precision spectroscopy with a single 40 Ca + ion in a Paul trap

“…15. [52] In our experiment, the two optical frequency standards have similar structures and 054213-9 share the 397 nm, 866 nm, 854 nm, and 729 nm lasers. Two AOMs (AO3 and AO4) are used to cover the difference between the clock transition frequency and the super cavity's resonant frequency.…”

Correlation between the magic wavelengths and the polarization direction of the linearly polarized laser in the Ca + optical clock

“…866 nm repumping laser 854 nm quenching laser The optical clock system consists of a 729 nm narrow line-width laser, a single ion trapping system, and a closedloop locking module, which has been described in previous work. [28][29][30][31] The 729 nm laser has a linewidth of less than 5 Hz, and the instability of the laser is 1×10 −14 for 20 s. For the ∼ 17 s feedback circle, the error due to the drift of the 729 nm probe laser for one measurement of the light shift of the clock transition can be smaller than 4 Hz, corresponding to ∼ 3 pm of the magic wavelength. The L m laser is the key element in the measurement of the magic wavelength, so the L m laser used in the experiment is frequency stabilized using a transfer cavity referenced to the 729 nm probe laser, and the long-term drift is reduced to less than 10 MHz within 4 h. An unpolarized beam splitter (BS) is used to split a part of the beam to a photodiode (PD) for monitoring the power of the L m laser, which is also shown in Fig.…”

A cryogenic radio-frequency ion trap for a 40Ca+ optical clock

“…For 40 Ca + optical clocks, BBR can induce the Stark shift of ∼ 0.35 Hz at room temperature. [26][27][28] The uncertainty from this frequency shift also dominates the uncertainty budget table of a Ca + optical clock. It scales proportionally with the fourth power of the ambient temperature (T 4 ) [29,30]…”