Although QE may be justified by weak economic and growth fundamentals, keeping rates too low for too long can eventually feed such bubbles. That is what happened in 2000-2006, when the US Federal Reserve aggressively cut the federal funds rate to 1% during the 2001 recession and subsequent weak recovery and then kept rates down, thus fueling credit/housing/subprime bubbles.
尽管疲软的经济和增长基本面可能为QE提供支持，但将过低利率维持过久最终会引发泡沫。2000~2006年已经发生过这一幕，当时美联储为了应对2001年衰退及其后的经济疲软，将联邦基金利率基金地降到1%并长期维持在低位，从而导致了次贷泡沫。