  We present a new approach for implementing a $\sqrt{\rm swap}$ gate between
two spatially far apart sites connected by a large-size coupled cavity array as
quantum bus. The duration is only related to the parity of cavity number but
independent of a specific number of cavity, thus it is possible to process
quantum information in an arbitrary long distance in principle without time
varied. Referring to the recent experimental progresses on coupled-cavity
array, we also make an assessment of the scalability and take the cavity number
$N$ = 5 as an example to illustrate the robustness of our proposal via quantum
process tomography.
