  The bulk nuclear matter produced in heavy ion collisions carries a multitude
of conserved quantum numbers: electric charge, baryon number, and strangeness.
Therefore, the diffusion processes associated to these conserved charges cannot
occur independently and must be described in terms of a set of coupled
diffusion equations. This physics is implemented by replacing the traditional
diffusion coefficients for each conserved charge by a diffusion coefficient
matrix, which quantifies the coupling between the conserved quantum numbers.
The diagonal coefficients of this matrix are the usual charge diffusion
coefficients, while the off-diagonal entries describe the diffusive coupling of
the charge currents. In this paper, we show how to calculate this diffusion
coefficient matrix from kinetic theory and provide results for a hadron
resonance gas and a gas of partons. We further find that the off-diagonal
entries can reach similar magnitudes compared to the diagonal entries. In order
to provide some insight on the influence that the coupling between the net
charge diffusion currents can have on heavy ion observables, we present first
results for the diffusive evolution of a hadronic system in a simple
(1+1)D-fluid dynamics approach, and study different configurations of the
diffusion matrix.
