one of my tents is 3'9"x3'9" and under a 1KW I have pulled over 600g a few times. Not spectacular yields but that should answer your question: yes, when dialed you can pull over a 1lb from that size space.
EDIT: ooh...that question was "HOW" could one yield that. Well step 1 is dial in your strain. if you're working with a tent, check out my current thread as it has lots of relevant info on growing in these size spaces.
Personally, in a 4x3 room, I would probably rock a 600w light above a 3x3 table with 25 plants in rows of 5x5 with 5" square pots, 0 days veg and trimmed SOG style and with a dialed strain I would expect around 1lb per harvest. DIAL IN YOUR STRAIN; that is key to success regardless of room size.
About 2 months ago I got 2lbs from 7 girls supper cropped in a 4x4 2 600w
I'm doing 4 girls under a screen in a 3x3 be interesting to see what makes of that.
SB2
-a scrog with a seasons worth of veg time so that the colas are fucking huge and tall as shit
-a 45gl rez
-a 55gl rez
the plant is seated in the 45gl; the 45gl is connected to the 55gl (or a 275gl IBC tote) via float valve and let that shit go for about 4 months until there is not one square left on the screen and then flower that bitch!