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

Rachel Elvin, Gregory W. Hoth, Michael W. Wright, Ben Lewis, Alan Bregazzi, Brendan Keliehor, Aidan S. Arnold, Paul F. Griffin, Erling Riis

Published Feb 25, 2020• 0 citations
Publisher

Abstract

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.

DOI
10.1117/12.2552587

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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.
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.
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 10 7 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.
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 10710^7107 87^{87}87Rb atoms, which are subsequently cooled to 20 μ20\,μ20μK in optical molasses. We optically probe the microwave atomic ground-state splitting using lin⊥\perp⊥lin polarised coherent population trapping and a Raman-Ramsey sequence. With ballistic drop distances of only 0.5 0.5\,0.5mm, the measured short-term fractional frequency stability is 2×10−11/τ2 \times 10 ^{-11} /\sqrtτ2×10−11/τ​.
Abstract A compact platform for cold atoms opens a range of exciting possibilities for portable, robust and accessible quantum sensors. In this work, we report on the development of a cold-atom microwave clock in a small package. Our work utilises the grating magneto-optical trap and high-contrast coherent population trapping in the lin ⊥ $\perp $ lin polarisation scheme. We optically probe the atomic ground-state splitting of cold 87Rb atoms using a Ramsey-like sequence whilst the atoms are in free-fall. We have measured a short-term fractional frequency stability of 5 × 10 − 11 / τ 5×10−11/τ5{\times}{10}^{-11}/\sqrt{\tau }5×10−11/τ​ with a projected quantum projection noise limit at the 10 − 13 / τ 10−13/τ{10}^{-13}/\sqrt{\tau }10−13/τ​ level.
The combination of coherent population trapping (CPT) physics and grating magneto-optical trap (GMOT) holds a potential of developing the next generation high performance compact atomic clock. In this work, we aim to build a Rb atomic clock that combining double-modulation coherent population trapping (DM-CPT) in GMOT system. In order to maximize the atoms trapped in clock transition, circularly polarization laser beam is replaced by modulated σ+and σ-beam, with which high-contrast and narrow-linewidth CPT signal could be observed. Also the GMOT system is designed for the interrogation of laser-cooled atoms. This work could provide foundation of high performance compact cold-atom CPT clock.
We present a coherent population trapping clock system based on laser-cooled 87Rb atoms. The clock consists of a frequency-stabilized CPT interrogation laser and a cooling laser as well as a compact magneto-optical trap, a high-performance microwave synthesizer, and a signal detection system. The resonance signal in the continuous wave regime exhibits an absorption contrast of ∼ 50%. In the Ramsey interrogation method, the linewidth of the central fringe is 31.25 Hz. The system achieves fractional frequency stability of 2.4 × 10 − 11 / τ , which goes down to 1.8 × 10−13 at 20000 s. The results validate that cold atom interrogation can improve the long-term frequency stability of coherent population trapping clocks and holds the potential for developing compact/miniature cold atoms clocks.