The disclosure relates to a gravity gradiometer including a pair of magneto-optical traps for measuring a gravity gradient. A cold atom gravity gradiometer system includes comprising: first and second magneto-optical traps, each having a plurality of mirrored surfaces arranged to reflect an incident laser beam to trap respective first and second cold atom clouds separated from each other by a separation distance; an optical subsystem arranged to transmit a first laser beam in a first direction along a first longitudinal axis towards the first magneto-optical trap and a second laser beam in an opposite second direction along a second longitudinal axis towards the second magneto-optical trap, the second longitudinal axis being parallel to the first longitudinal axis.