Fighting excessive deflation once interest rates have been reduced to zero

Fighting excessive deflation is in some ways more difficult than fighting hyperinflation.

During inflationary times, there is basically no limit to how much central banks can raise interest rates.

But in the battle against deflation, once interest rates have been reduced to zero, there is little that central banks can do to stimulate further growth.  

The two things that can be done once interest rates reach zero are:

• negative interest rates or 
• quantitative easing.