Performance of a prototype atomic clock based on lin‖lin coherent population trapping resonances in Rb atomic vapor

Abstract

We report on the performance of the first table-top prototype atomic clock based on coherent population trapping (CPT) resonances with parallel linearly polarized optical fields (lin||lin configuration). Our apparatus uses a vertical cavity surface emitting laser (VCSEL) tuned to the D1 line of 87 Rb with current modulation at the 87 Rb hyperfine frequency. We demonstrate cancellation of the first-order light shift by proper choice of rf modulation power, and further improve our prototype clock stability by optimizing the parameters of the microwave lock loop. Operating in these optimal conditions, we measured a short-term fractional frequency stability (Allan deviation) 2×10for observation times 1 s ≤ τ ≤ 20 s. This value is limited by large VCSEL phase noise and environmental temperature fluctuation. Further improvements in frequency stability should be possible with an apparatus designed as a dedicated lin||lin CPT resonance clock with environmental impacts minimized.In the recent decades impressive progress has been made in development of miniature precision measurement devices (clocks, magnetometers, gyroscopes, etc.) that use atomic energy levels as a reference [1,2,3,4,5,6,7,8,9,10]. A promising scheme for all-optical interrogation of a microwave clock transition in chip-scale atomic devices is based on the modification of optical properties of an atomic medium under the combined action of multiple resonant optical fields. For example, under the conditions of coherent population trapping (CPT) simultaneous action of two optical fields [as shown in Fig. 1(a)] allows "trapping" atoms in a non-interacting coherent superposition of two long-lived hyperfine sublevels of the ground energy state |g 1,2 that, under idealized conditions (isolated three-level scheme, no groundstate decoherence), is completely decoupled from the excited state |e . Such non-interacting state (usually called "dark state") exists only when the differential frequency of two optical fields (two-photon detuning) matches the energy splitting of the hyperfine states, and leads to a narrow peak in optical transmission -the effect known as electromagnetically induced transparency, or EIT [11]. The linewidth of a CPT resonance depends on the intensities of the optical fields, but it is ultimately limited by the finite interaction time of atoms with light. Since it is possible to obtain CPT resonances as narrow as a few tens to hundreds of Hz [12,13], one can lock a microwave oscillator controlling the frequency difference between two optical fields such that its output frequency is stabilized at the atomic transition frequency |g 1 − |g 2 [14]. Frequency stability of such atomic clocks improves for a high-contrast narrow CPT resonance. Also, minimal sensitivity of the CPT resonance frequency to the experiment environmental fluctuations (such as temperature, laser frequency and power) is required to ensure longterm stable operation of the clock. * Corresponding author: inovikova@physics.wm.edus FIG. 1: (a)Idealized three-level Λ system that a...

Coherent-population-trapping resonances with linearly polarized light for all-optical miniature atomic clocks

“…In practice, however, the frequency stability will also be limited by residual intensity noise that depends strongly on the linewidth of the laser [22,23]. Recently, a table-top prototype atomic clock based on lin||lin CPT resonances with a short-term fractional frequency stability 2 × 10 −11 τ −1/2 was demonstrated [24].…”

Measurements of the magnetic field vector using multiple electromagnetically induced transparency resonances in Rb vapor

“…2) are similar to those used for miniature EIT-based magnetometers [10] (although most components are not miniaturized). The details of the construction and operation of our experimental apparatus are given in [23,25]. A temperature-stabilized vertical cavity surface-emitting diode laser (VCSEL) was current-modulated at ν m = 6.8347 GHz with the laser carrier frequency tuned at 5S 1/2 F = 2 → 5P 1/2 F ′ = 1 transition and the first modulation sideband resonant with 5S 1/2 F = 1 → 5P 1/2 F ′ = 1 transition (see Fig.…”

Towards a compact cold atom frequency standard based on coherent population trapping

“…The lin||lin configuration was first proposed and studied by Taichenachev et al in [5] and then investigated further in [6], [7], [8], [9], [10]. This scheme is most efficient when the coupling occurs between ground states of total angular momenta F = 1, 2 and an excited state of total angular momentum F = 1.…”