Frequency Stability of Atomic Clocks Based on Coherent Population Trapping Resonance in ^85Rb

Mikko Merimaa, Thomas Lindvall, Ilkka Juhani Tittonen +1 more

Mikko Merimaa, Thomas Lindvall, Ilkka Juhani Tittonen +1 more

An all-optical microwave frequency standard based on coherent population trapping (CPT) in 85Rb is developed. The CPT resonances are detected by an ordinary edge-emitting diode laser in a simple optical setup. A buffer-gas mixture is carefully optimized to yield a narrow linewidth and a reduced temperature dependence of the resonance frequency. With the developed system we are able to measure ultranarrow optically induced hyperfine CPT resonances at <20 Hz, which is in good agreement with the linewidth calculated from experimental parameters. The frequency of an RF-signal generator has been stabilized to the CPT resonance between the two mF=0 magnetic sublevels. The relative frequency stability (square root of Allan variance) follows a slope of 3.5×10-11 τ-1/2(1 s<τ<2000 s). The best stability of 6.4×10-13 is reached at an integration time of τ=2000 s. This stability is sufficient for many high-precision applications. Frequency-shift measurements were made to evaluate the frequency dependencies on the operation parameters.

Ke Deng, Xuzong Chen, Zhong Wang

This paper introduce three main technologies in our coherent population trapping clock. The rubidium vapor cell is fabricated by glass-silicon anodic bonding techniques. We use two different buffer gases (Ar and Ne) that produce opposite shift rates to reduce the dependence of the clock frequency stability on the temperature stability of the atoms. We use the ceramic-filled coaxial resonator as the RF resource.

Jaques Vanier

Vishal Shah, John E. Kitching

Shigeyoshi Goka

In this paper, the investigation of a 85 Rb coherent-population-trapping (CPT) atomic clock for low-power operation is described. The modulation profiles and CPT resonances for both 85 Rb and 87 Rb, the long-term frequency stabilities of the CPT resonance for both, and the feasibility of switching between low-power and high-stability operation modes are presented. The choice of 85 Rb rather than conventional 87 Rb is dictated by the lower ground-state hyperfine-splitting frequency, which leads to less than one-half the required RF power and more effective RF-related circuit designs. CPT resonances for both 85 Rb and 87 Rb can be observed separately in the same natural mixture Rb gas cell, and the linewidth is less than 120 Hz in both cases. The long-term frequency stabilities are <4.0 ×10 -12 /day for 85 Rb and <3.5 ×10 -12 /day for 87 Rb. These results indicate that a 85 Rb CPT atomic clock has a long-term stability of ∼4.0 ×10 -12 /day and consumes about one-half the RF power of a 87 Rb equivqlent. In addition, it is possible to switch between low-power and high-stability operation modes by changing the RF frequency and power.