  We report a measurement of the condensation energy of a two-component Fermi
gas with tunable interactions. From the equation of state of the gas, we infer
the properties of the normal phase in the zero-temperature limit. By comparing
the pressure of the normal phase at T=0 to that of the low-temperature
superfluid phase, we deduce the condensation energy, i.e. the energy gain of
the system in being in the superfluid rather than normal state. We compare our
measurements to a ladder approximation description of the normal phase, and to
a fixed node Monte-Carlo approach, finding excellent agreement. We discuss the
relationship between condensation energy and pairing gap in the BEC-BCS
crossover.
