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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

Progress Towards a Compact Cold-Atom Microwave Clock

Martin Knapp, S Walby, Mohsin Haji, Christopher J. Foot, Patrick Robert Gill

Published May 15, 2023• 0 citations
Publisher

Abstract

Here we present progress towards a compact cold-atom microwave clock. The system we have developed is currently a demonstrator for a clock architecture whereby a cloud of laser-cooled caesium atoms are dropped and interrogated during free fall. We describe the experimental sequence as well as show preliminary results related to signal-to-noise ratio limits and Rabi microwave spectroscopy.

DOI
10.1109/eftf/ifcs57587.2023.10272192

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Here we present progress towards a compact cold-atom microwave clock. The system we have developed is currently a demonstrator for a clock architecture whereby a cloud of laser-cooled caesium atoms are dropped and interrogated during free fall. We describe the experimental sequence as well as show preliminary results related to signal-to-noise ratio limits and Rabi microwave spectroscopy.
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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.
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We present the performance of a compact microwave interrogated atomic clock based on laser cooled 87^{87}87Rb\rm{Rb}Rb atoms. The clock utilizes a micro-fabricated grating magneto-optical trap (gMOT) to cool and trap atoms, and an additively manufactured microwave cavity for microwave interrogation. We demonstrate a signal-to-noise ratio (SNR) of 370370370 at a 1 Hz bandwidth and mid-term instability of 6.7×10−146.7\times10^{-14}6.7×10−14 at an averaging time of τ=3×104τ=3 \times 10^{4}τ=3×104 s. In addition, a low cost mu-metal foil has been implemented on the vacuum chamber to reduce the quadratic Zeeman shift which was previously limiting stability beyond τ=10τ= 10τ=10 s.