In the U.S., the interest rates set by the Federal Reserve get lower and lower. They may even hit zero at some point (probably only for very short periods of lending). This means that they would be allowing banks to borrow over time, at no cost.
Apparently, the U.S. government would be willing to take the risk of lending out, without hope of any return to compensate for the risk. The theory is that the stimulation to the economy - in the medium term - outweighs the risk to the government in the short term.
Rates to businesses would remain above zero, because banks need to operate at a margin to make a profit.
The more risk the U.S. government takes on, the more it intertwines its fate with that of the economy it oversees. And the more vulnerable it becomes to anyone who wants to disempower it by financial means.
