Nikon 1 J3 has a 14.0MP 1" (13.2 x 8.8 mm ) sized CMOS sensor . On the other hand, Panasonic G1 has a 12.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor .
Below you can see the 1 J3 and G1 sensor size comparison.
As seen above, Panasonic G1 has a 1.9x Larger sensor area than Nikon 1 J3. 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.