  We report measurements of charge configurations and charge transfer dynamics
in a hybrid single-electron box composed of aluminum and copper. We used two
single-electron transistors (SETs) to simultaneously read out different parts
of the box, enabling us to map out stability diagrams of the box and identify
various charge transfer processes in the box. We further characterized the
elastic cotunneling in the box, which is an important source of error in
electron turnstiles consisting of hybrid SETs, and found that the rate was as
low as 1 Hz at degeneracy and compatible with theoretical estimates for
electron tunneling via virtual states in the central superconducting island of
the box.
