Sony a5000 has a 20.0MP APS-C (23.2 x 15.4 mm ) sized CMOS sensor and features Bionz X processor. On the other hand, Olympus E-PM2 has a 16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor .
Below you can see the a5000 and E-PM2 sensor size comparison.
As seen above, Sony a5000 has a 1.6x Larger sensor area than Olympus E-PM2. 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.