  Electronic quantum entanglement between the central chain and the two
electrodes in an infinite one-dimensional two-probe device system is studied.
The entanglement entropy is calculated employing the nonequilibrium Green's
function method in the tight-binding model based on the relation between the
correlation matrix and the von Neumann entropy. By extending the entropy to
nonequilibrium cases, we have studied the scaling behavior when a voltage bias
is applied between the two electrodes. The entropy usually decreases with the
bias and may jump up when a quasi-state in the chain aligns in energy with the
band edges in the electrodes. Odd-even effect is observed due to the symmetry
of the chain.
