Well, not exactly at Ephesus, but only 4 km (2.5 miles) west of the archeological site, and 7 km (4.3 miles) west of Selçuk. This photo looks north from the Kuşadası end of the beach.
The sand at Pamucak is fine but darkish in color, and there’s plenty of it. The beach is relatively undeveloped (as you can see), which is both good and bad: there are not a lot of hotels, shops, bars and restaurants to clutter it up.
But also, there are not a lot of hotels, shops, bars and restaurants if you need some.
Pamucak is great for a leisurely swim after a morning spent strolling through the ruins at Ephesus. In summer, dolmuses and taxis make the short run from Selçuk and Ephesus to the beach frequently.