Sheikh Sâmî al-Mâjid
The government does not receive or take anything from the $4000 dollars deposited by the person, so the money deposited is solely for the bank and what comes from the government is therefore purely a contribution from the government. This means that with respect to the government contribution, there is no usury.
This is because the party that contributes the extra funds to the account (the government) is different than the party that receives the annual deposit of 4000 dollars (the bank).
May Allah guide us all.
Source: Islam Today