What are the differences between quantitative easing and helicopter money?

Quantitative easing is pure monetary policy: the central bank buys bonds and pays by creating money. Quantitative easing has an effect on the economy if the behaviour of the sellers of bonds change s when they hold money from when they hold bonds. If money and bonds are highly substitutable, quantitative easing has no effect: for economic agents, it makes no difference whether they hold money or bonds . If money and bonds are imperfectly substitutable, quantitative easing has an effect on the economy because long-term interest rates fall and also because the money is reinvested in other assets (financial or real estate). Helicopter money, which was created in response to the COVID crisis, is a combination of an expansionary fiscal policy and quantitative easing: government transfer payments to economic agents are ultimately financed by money creation; it is as if the central bank transferred money to economic agents. The effect of helicopter money is the sum of the effects of the expansionary fiscal policy and quantitative easing: stimulation of demand without rising interest rates, rising asset prices if money and bonds are not perfectly substitutable.