  We introduce and demonstrate double-bright electromagnetically induced
transparency (D-EIT) cooling as a novel approach to EIT cooling. By involving
an additional ground state, two bright states can be shifted individually into
resonance for cooling of motional modes of frequencies that may be separated by
more than the width of a single EIT cooling resonance. This allows
three-dimensional ground state cooling of a $^{40}$Ca$^+$ ion trapped in a
linear Paul trap with a single cooling pulse. Measured cooling rates and
steady-state mean motional quantum numbers for this D-EIT cooling are compared
with those of standard EIT cooling as well as concatenated standard EIT cooling
pulses for multi-mode cooling. Experimental results are compared to full
density matrix calculations. We observe a failure of the theoretical
description within the Lamb-Dicke regime that can be overcome by a
time-dependent rate theory. Limitations of the different cooling techniques and
possible extensions to multi-ion crystals are discussed.
