Abstract
Clocks based on cold atoms offer unbeatable accuracy and long-term stability, but their use in portable quantum technologies is hampered by a large physical footprint. Here, we use the compact optical layout of a grating magneto-optical trap (gMOT) for a precise frequency reference. The gMOT collects 107 87Rb atoms, which are subsequently cooled to 20 µK in optical molasses. We optically probe the microwave atomic ground-state splitting using lin⊥lin polarised coherent population trapping and a Raman-Ramsey sequence. With ballistic drop distances of only 0.5 mm, the measured short-term fractional frequency stability is 2×10-11/τ.
Highlights
Cold atoms hold great promise as a medium in which ultralow-drift metrology can be achieved with excellent precision across a wide range of relevant physical observables, e.g. time [1], acceleration [2], rotation [3] and magnetic fields [4]
We present an 87Rb grating magneto-optical trap (gMOT)-based cold-atom microwave clock [27] (Fig. 1), as a test-bed to investigate the combination of the gMOT with coherent population trapping (CPT) using pulsed Ramsey-like probing
We compare the phase of the CPT components in our probe by measuring a beatnote between light picked off by the 70/30 NPBS in Fig. 2(b) and a commercial microwave source operating at a frequency close to the ground-state splitting frequency
Summary
Cold atoms hold great promise as a medium in which ultralow-drift metrology can be achieved with excellent precision across a wide range of relevant physical observables, e.g. time [1], acceleration [2], rotation [3] and magnetic fields [4]. From a single input trapping laser beam (Fig. 1), gMOTs have demonstrated trapped atom numbers ≈ 108 comparable to regular 6-beam MOTs with the same beam overlap volume They can reach sub-Doppler optical molasses temperatures, with. There are several high-contrast CPT polarisation schemes including: lin lin [29,30], lin⊥lin [31], push-pull optical pumping (PPOP) [32], and σ+ − σ− [33,34,35] These techniques have been applied to both thermal vapour-cell and laser-cooled atoms. With ultra-cold 87Rb but employing single-laser lin⊥lin CPT, we achieve comparable short-term stability of 2 × 10−11/√τ, with a compact gMOT rather than the conventional 6-beam MOT
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