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Conference on Precision Electromagnetic Measurements

Current status of an atomic gravimeter developing at KRISS

Sang-Bum Lee, Sang Eon Park, Dai-Hyuk Yu, Chang Yong Park, Won-Kyu Lee, Taeg Yong Kwon

Published Jul 1, 2012• 0 citations
Publisher

Abstract

We present a current status of an atomic gravimeter, which is based on Mach-Zehnder-type atom interferometer using stimulated Raman transition, developing at KRISS. Cooling beams with (111) geometric configuration was used for magnetic optical trap (MOT). Rubidium87(Rb87) atoms are trapped and cooled in MOT. Temperature of the trapped atoms was measured to be about 1.7μK by time of flight measurement after a deep cooling.

DOI
10.1109/cpem.2012.6251079

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Conference on Precision Electromagnetic Measurements•Jul 1, 2012•0 citations
We present a current status of an atomic gravimeter, which is based on Mach-Zehnder-type atom interferometer using stimulated Raman transition, developing at KRISS. Cooling beams with (111) geometric configuration was used for magnetic optical trap (MOT). Rubidium87(Rb87) atoms are trapped and cooled in MOT. Temperature of the trapped atoms was measured to be about 1.7μK by time of flight measurement after a deep cooling.
This paper introduces an atomic gravimeter under development at KRISS for precise measurement of gravitational acceleration. The gravimeter based on atom interferometer uses two counter-propagating Raman lasers of π/2-π-π/2 pulse sequence and laser cooled87Rb atoms in free fall. Atomic interference fringes caused by Raman lasers were observed at various time intervals between the three Raman pulses. The frequency sweep rate α which compensates Doppler shift due to gravitational acceleration g was obtained from the interference fringes. In the presentation, the current status and recent results of the KRISS atomic gravimeter will be discussed.
This thesis describes the construction of a portable cold atom gravimeter with the aim to be employed in remote locations. Two species of alkali atoms would be eventually used, namely Rubidium-87 and Cesium-133. The advantage of such a system is shorter duty cycle, and shorter dead time. In this thesis we focus on the experimental realization of a Rubidium-87 gravimeter, using the Ramsey-Bord´e interferometry method first described by C. Bord´e, and employed by Kasevich et. al. Approximately 10^8 atoms are laser cooled and trapped to a MOT and further cooled by a optical molasses to a temperature of 12μK. Two counterpropagating Raman beams separated by a frequency matching the ground state hyperfine splitting will be used to excite stimulated Raman transitions to place the atoms into a superposition of the two ground metastable states. This thesis describes in detail the vacuum system and the laser systems built to cool and trap the atoms and to produce the Raman beams to perform the Ramsey sequence. The thesis covers also the relevant theory related to our experiment.
Abstract The precision measurement of acceleration due to gravity (g) for potential scientific and industrial applications requires the use of absolute quantum gravimeters (AQGs) as quantum sensors. In this study, the development of magneto-optical trap (MOT) for the Rubidium-87 ( 87 Rb) atoms for integration into an atomic gravimeter has been discussed. The MOT serves as a critical component for the cooling and trapping of neutral atoms, providing a high flux, low temperature atomic ensemble for subsequent measurements in cold atomic physics, such as inertial navigation, exploration, and gravity mapping. Our setup emphasizes compactness without compromising atom number or temperature performance using the single 780 nm extended cavity diode laser. We have presented the optimized optical layout for efficient atom cooling, trapping, and detection. The obtained results show atom loading rate of ∼6.02 × 10 8 atoms within 221 ms that provides fast data acquisition for the entire cycle of AQG. The fluorescence signal from free falling MOT is also obtained, which provides time-of-flight of 211 ms and temperature of 57 μK. The system is robust against environmental perturbation and offers valuable insights into the advancement of atomic ensemble for the realization of high precision quantum sensors for geophysical and navigation applications.
The cold atomic gravimeter (CAG) has the advantage of high measurement accuracy and does not need to be calibrated on a regular basis. To achieve cold atom interference, it is first necessary to cool and trap the atoms by magneto-optical trap (MOT). However, there are many types of MOTs, and their trapping and cooling results directly affect the atomic interference, and thus, the measurement accuracy of a CAG. MOTs should be designed or selected correctly for different application needs. This paper reviews the research history of MOTs and analyzes their structure and principles. The current status of applications of different types of MOTs is highlighted. Their advantages and disadvantages are summarized, and perspectives for the development of MOTs for cold atomic gravimetry are presented.
A light-pulse atom interferometer for inertial sensing applications such as gravimetry is being commissioned, where the prototype has a target relative precision (σ g /g) of one part per million to enable geophysics applications, which is three orders of magnitude less sensitive than commercial optical gravimeters, but with the potential to exceed these. As part of this, a rubidium-85 magneto-optical trap was upgraded using optical amplification and fibre optics to capture an atom population number of O(10 8 ) and sub-Doppler cooling techniques have been used to reach ultracold temperatures of 20 μK. Several interferometer subsystems have been developed, including extensive optical systems featuring a high-specification optical modulator and laser-induced fluorescence detection. Preliminary investigations into the coherent manipulation of atomic states have been implemented and the resonance peak of a stimulated Raman transition has been observed.