Towards a compact atomic clock based on coherent population trapping and the grating magneto-optical trap

Abstract

The combination of coherent population trapping (CPT) and laser cooled atoms is a promising platform for realizing the next generation of compact atomic frequency references. Towards this goal, we have developed an apparatus based on the grating magneto-optical trap (GMOT) and the high-contrast lin ⊥ lin CPT scheme in order to explore the performance that can be achieved. One important trade-off for cold-atom systems arises from the need to simultaneously maximize the number of cold atoms available for interrogation and the repetition rate of the system. This compromise can be mitigated by recapturing cold atoms from cycle to cycle. Here, we report a quantitative characterization of the cold atom number in the recapture regime for our system, which will enable us to optimize this trade-off. We also report recent measurements of the short-term frequency stability with a short-term Allan deviation of 3 × 10 −11 / √ τ up to an averaging time of τ = 10 s.

Cold-atom clock based on a diffractive optic

“…We prepare 10 7 atoms in the gMOT using trap and repump light from two external cavity diode lasers (ECDLs) [40], stabilised with saturated absorption spectroscopy (SAS). We achieve a large atom number with a short load time of 80 ms by recapturing the cold atoms between experimental cycles [41,42]. The 2 × 2 cm 2 microfabricated grating chip [43], consists of three linear gratings with the grooves forming equilateral triangles, and is situated beneath the glass vacuum chamber ( Fig.…”

“…This is used as the master oscillator to phase-lock our local oscillator (LO) and reduce the additional phase noise. Further information on the PLL can be found in [42].…”

“…We characterize the CPT resonances in our system by measuring the steady-state transmission of the first pulse as a function of the LO frequency. We measure Ramsey-CPT fringes by integrating the initial transient in the second detection pulse, with laser intensity noise suppressed using a double-ratio method [29,30,33,42].…”

Impact of Laser Frequency Noise in Coherent Population Trapping with Cold Atoms

“…In order to investigate the achievable performance with cold atoms and CPT, we employ an apparatus that combines a compact magneto-optical trap formed by an optical diffraction grating (GMOT) [15] with linlin CPT [16]- [19]. Our system has been described in [20]- [22], and it is shown schematically in Fig. 1.…”

“…In order to suppress this phase noise, we implement a phase-locked loop (PLL) by detecting the phase of the beatnote between the light from AOM 1 and the first-order sideband from the EOM and feeding back to our EOM driver. The implementation of the PLL is described in more detail in [22].…”