Sovereign debt markets around the world are under heavy pressure, particularly the long end of the curve, where yields have recently shot up to historic highs in many countries. And in the case of Japan, record highs.There's nothing magical about the $3 trillion figure, and it is probably well above the unknowable level where officials reckon reserves are still "ample". But it brings into focus Fed QT and the question of how low can reserves go without sparking liquidity concerns. Fed Governor Christopher W ...