Raman-Ramsey CPT with a grating magneto-optical trap

We describe an experiment which combines cold 87Rb atoms from a grating magneto-optical trap (GMOT) with Lin-perp-Lin coherent population trapping (CPT) and pulsed Ramsey interrogation. The bichromatic fields required for Lin-perp-Lin are generated by combining light from a single external cavity diode laser (ECDL) with an electro-optic modulator (EOM) and an acousto-optic modulator (AOM). With this laser system and the GMOT, we are able to produce Raman-Ramsey fringes using either the F' = 1 or the F' = 2 excited states of the 87 Rb D1 line. As a step towards realising a frequency standard based on the GMOT, we measure the Ramsey fringe amplitude as a function of the magnetic bias field and the excited state. We observe dark state interference with F' = 1 and show that this interference is suppressed with F' = 2, as expected from prior work on CPT with 87Rb in thermal vapour cells

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

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

High-Performance Silicon Photonic Single-Sideband Modulators for Cold Atom Interferometry

The most complicated and challenging system within a light-pulse atom interferometer (LPAI) is the laser system, which controls the frequencies and intensities of multiple laser beams over time to configure quantum gravity and inertial sensors. The main function of an LPAI laser system is to perform cold-atom generation and state-selective detection and to generate coherent two-photon process for the light-pulse sequence. Substantial miniaturization and ruggedization of the laser system can be achieved by bringing together most key functions of the laser and optical system onto a photonic integrated circuit (PIC). Here we demonstrate a high-performance silicon photonic carrier-suppressed single-sideband (CS-SSB) modulator PIC with dual-parallel Mach-Zehnder modulators (DP-MZMs) operating near 1560 nm, which can dynamically shift the frequency of the light for the desired function within the LPAI. Independent RF control of channels in SSB modulator enables the extensive study of imbalances in both the optical and RF phases and amplitudes to simultaneously reach 30 dB carrier suppression and unprecedented 47.8 dB sideband suppression with peak conversion efficiency of -6.846 dB (20.7 %). Using a silicon photonic SSB modulator with time-multiplexed frequency shifting in an LPAI laser system, we demonstrate cold-atom generation, state-selective detection, and the realization of atom interferometer fringes to estimate gravitational acceleration, $g \approx 9.77 \pm 0.01 \,\rm{m/s^2}$, in a Rubidium ($^{87}$Rb) atom system.Comment: 18 pages, 9 figure

Impact of laser frequency noise in coherent population trapping with cold atoms

Laser-cooled atoms and coherent population trapping (CPT) are promising tools for realizing a compact microwave frequency reference with excellent stability. To realize a high performance device, it is necessary to understand and minimize all sources of technical noise. Here, we investigate the role of laser frequency noise in cold-atom CPT with an apparatus based on the grating magneto-optical trap (GMOT). We compare the performance of our setup with an external cavity diode laser (ECDL) and a distributed feedback diode laser (DFB). With the DFB, laser frequency noise is one of the dominant noise sources in our system. With the ECDL, it is significantly reduced. We also report frequency stability measurements of our apparatus with a short-term Allan deviation Sigma_y (tau) ≈ 3(times)10-11/rt τ up to τ= 10 s

Progress of a compact microwave clock based on atoms cooled with a diffractive optic

An atomic clock based on a compact source of cold atoms and coherent population trapping (CPT) is an encouraging goal for future low-volume atomic frequency references. Our experiment seeks to investigate the performance of such a system by applying CPT in a high-contrast lin⊥lin polarisation scheme to our 87Rb grating magneto optical trap (GMOT) apparatus. In this paper, we report on our progress of improving short- term stability of our cold-atom CPT apparatus. Our recent measurements have shown a short-term stability of 5 x 10-11/√τ, with the ability to average down for times τ>100s