does that really work? inflation is a backward looking metric and interest rates are forward looking.

this is just about making a prediction of the future.

if you believe that inflation will decrease then your guaranteed rate of return from interest rates is great.

if you believe that inflation will increase or stay the same, then yes we have "negative interest rates"

I don't think it's reasonable to call it a "real" interest rate, because I can't buy T bills against it and it has no guarantees