I've looked at a dozen tutorials on removing background in Photoshop, and they all seem to do the same thing. I've followed the usual route of "create a new layer - select your subject - invert selection - press Delete" as described, for example, here. In itself, it does what it should no problem. However, the sharp cut-off from 0 % transparency (the subject) to 100% transparency (background) creates a pixelated edge, extremely visible when placing a dark subject on solid background.
How can I blur/antialias this edge with a small radius, 1-2 pixels, so that there is fade-out rather than cut-off? Note that this blur should only be present in the transparency channel, not the RGB image.