  At sufficiently high temperature and density, quantum chromodynamics (QCD)
predicts phase transition from the hadronic phase to the quark-gluon plasma
phase. Lattice QCD is the most useful tool to investigate this critical
phenomenon, which status is briefly reviewed. The usual problem in the
Lagrangian formulation at finite density is either an incorrect continuum limit
or its complex action and a premature onset of the transition as the chemical
potential is raised. We show how the difficulties are overcome in our
Hamiltonian approach.
