you couldn't vaporise the earth and maintain in in a localised gas ball similar to the gas giants because of its chemical make up...Its iron core will simply, under its own mass and thus its own gravitational force, be pulled into a solid mass as would the rest of the earths elemental and molecular make up.
unless you somehow propose to change the chemical balance of the earths contents so that under its current mass it would remain at a point where its pressure and gravity allow its chemical content to remain in a gaseous phase in space. then it would simply reform to a solid mass again
and the energy required to break the chemical bonds of the earths current molecular make up and then reform it into an entirely different chemical make up would be quite astronomical
so effectively what i'm saying is that whereas jupiter and saturn and predominantly hydrogen and uranus contain high proportions of methane and ammonia....they exist is gas phase because the balance between the pressure cause by it mass/gravity in balance with the temperature these pressures create...mean it exists as a gas..although uranus and neptune's atmophere's effectively solidify during their equivalent of winter and thus change their diameters