Both Nikon P340 and Fujifilm XQ2 have 12.0 MP resolution sensors but Nikon P340's sensor is 1/1.7" (7.44 x 5.58 mm ) and Fujifilm XQ2's sensor is 2/3" (8.8 x 6.6 mm ).
Since Fujifilm XQ2's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Nikon P340.
Below you can see the P340 and XQ2 sensor size comparison.
As seen above, Fujifilm XQ2 has a 1.4x Larger sensor area than Nikon P340. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.