Magneto-optical trapping in a near-suface borehole

Borehole gravity sensing can be used in a number of applications to measure features around a well, including rock-type change mapping and determination of reservoir porosity. Quantum technology gravity sensors, based on atom interferometry, have the ability to offer increased survey speeds and reduced need for calibration. While surface sensors have been demonstrated in real world environments, significant improvements in robustness and reductions to radial size, weight, and power consumption are required for such devices to be deployed in boreholes. To realise the first step towards the deployment of cold atom-based sensors down boreholes, we demonstrate a borehole-deployable magneto-optical trap, the core package of many cold atom-based systems. The enclosure containing the magneto-optical trap itself had an outer radius of (60 & PLUSMN; 0.1) mm at its widest point and a length of (890 & PLUSMN; 5) mm. This system was used to generate atom clouds at 1 m intervals in a 14 cm wide, 50 m deep borehole, to simulate how in-borehole gravity surveys are performed. During the survey, the system generated, on average, clouds of (3.0 & PLUSMN; 0.1) x 10(5 87)Rb atoms with the standard deviation in atom number across the survey observed to be as low as 8.9 x 10(4).

Automated summary

Borehole gravity sensing has various applications and can measure features around wells, such as rock-type changes and reservoir porosity. Quantum technology gravity sensors based on atom interferometry offer faster survey speeds and reduced need for calibration. However, improvements are needed in terms of robustness and reducing size, weight, and power consumption to deploy these devices in boreholes.