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Optical and Quantum Sensing and Precision Metrology II

Coherent population trapping and Ramsey interrogations in a cold atomic beam apparatus

G. S. Pati, Renu Tripathi, Gustavo Acosta, Mauricio Pulido

Published Mar 13, 2024• 0 citations
Publisher

Abstract

We are investigating coherent population trapping (CPT) and Ramsey-CPT interrogations in a cold atom system where the atomic beam originates from a pushed two-dimensional magneto-optical trap (2D+-MOT). Our results show promise for improving the performance of atomic clock using a cold atomic beam apparatus.
DOI
10.1117/12.3002917

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We present results from an atomic clock that employs a beam of cold 87Rb atoms and spatially separated (Ramsey) coherent population trapping interrogation of the hyperfine clock transition at 6.834 GHz. The cold atomic beam is generated through the use of a 2D+-magneto-optical trap. The interrogation is performed on the D2 line of 87Rb, and the optical fields use a counter-propagating σ+–σ− probing scheme. The use of cold atoms allows for relatively narrow Ramsey fringes even for a small spatial separation between the two interrogation zones (4.6 cm). The resulting clock has a short-term stability of 3×10−11/τ.
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.
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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.
The utilization of Ramsey interferometry via coherent population trapping (CPT), which enables the optical interrogation of microwave transitions without the reliance on microwave cavities, plays a crucial role in the advancement of compact and low-power quantum sensors. Particularly, high-resolution CPT-Ramsey spectroscopy of alkali-metal atoms has found extensive application in constructing miniaturized quantum sensors like atomic magnetometers and atomic clocks. Due to their well-defined environment and extended coherence time, cold atoms offer enhanced sensitivity and precision in CPT-Ramsey interferometry. This review comprehensively examines CPT-Ramsey interferometry with cold atoms, encompassing both conventional and multi-pulse techniques, and explores their potential applications in practical quantum sensors.