In his 2003 paper Escaping from a Liquidity Trap and Deflation: The Foolproof Way and Others Lars E.O. Svensson describes the liquidity trap experienced by countries such as Japan and lately the US, when central bank interest rates are close to zero percent.
If the nominal interest rate is initially low, which it is when inflation and expected future inflation are low, the central bank does not have much room to lower the interest rate further. But with deflation and expectations of deflation, even a nominal interest rate of zero percent can result in a substantially positive real interest rate that is higher than the level required to stimulate the economy out of recession and deflation. Nominal interest rates cannot fall below zero, since potential lenders would then hold cash rather than lend at negative interest rates. This is the socalled “zero lower bound for interest rates.”
In particular, conventional monetary policy seems unable to provide sufficient stimulus to the economy and address recession and deflation once the zero lower bound for interest rates has been reached. The problem is that the economy is then satiated with liquidity and the private sector is effectively indifferent between holding zero-interest-rate Treasury bills and money. In this situation, standard open-market operations by the central bank to expand the monetary base by buying Treasury bills lead the private sector to hold fewer Treasury bills and more money – but this has no effect on prices and quantities in the economy. When this “liquidity trap” occurs, expanding liquidity (the monetary base) beyond the satiation point has no effect. If a combination of a liquidity trap and deflation causes the real interest rate to remain too high, the economy may sink further into a prolonged recession and deflation.