There are two forms of interest rates: nominal and real.
Nominal is what the number says, as in "this account yields 2% interest" or whatever.
Real is what that number is minus inflation. So, if your account yields 2% interest per year, but inflation is 8% per year, your real rate of return is -6% per year (i.e., you are losing 6% of your purchasing power per year).
Today, some countries' bonds have negative nominal yield. You can buy a bond for $100, say, and get $80 back at the end of 30 years.
And we have negative real rates in most countries currently, including the US. (Official inflation is 7.5%. But the official measure understates real inflation by substituting hamburger for steak if steak gets expensive (hedonics). Using 1990 basket of goods, inflation is currently 11%. See
http://www.shadowstats.com/alternate_data/inflation-charts )
In both cases, people are paying the borrower for the privilege of loaning it money. A great gig while it lasts.
Why would anyone buy bonds in that situation? Three reasons. First is that some places (pension funds, for example) have to put their money in government bonds according to to their own internal regulations. Second is that large amounts of money are cumbersome to turn into paper currency and vault it -- takes time and reduces fluidity of using the funds. And if it's not in paper currency, it's in a debt instrument of some sort (bond, CD, money-market account, etc.), not paper dollars in a vault. Third is that, even though a negative-yielding bond is a rip off, if interest rates go even more negative, the bonds you have go up in value, and then you can sell them (i.e., speculation in bond prices).
Countries with paper currency can't go too negative on rates, or people withdraw their money as paper and vault it. But, if you have only electronic funds and EBT-type cards, the government can go to whatever rates it wants, negative or not. There is no paper money to take out and vault. Also, you can give out stimulus and have conditions on it, like "this money goes away if you don't spend it by this date" or "this money can be used to buy only these things, but not those things". And the government can track every purchase. That is why many governments want to go cashless. They will tell you the reason is to combat money laundering and illegal activity.