A high-pressure phase of atomic hydrogen predicted theoretically to form at the center of Jupiter, was first produced in the laboratory by Weir et al. (1996), at a pressure of 93-180 GPa and temperature of 2200-400 K.
Hydrogen
Ladbury, R. "Livermore's Big Guns Produce Liquid Metallic Hydrogen." Phys. Today 49, 17-18, May 1996.
Weir, S. T.; Mitchell, A. C.; and Nellis, W. J. Phys. Rev. Let. 76, 1860, 1996.