  We consider two driven cavities (capacitors) connected in series via an edge
state. The cavities are driven such that they emit an electron and a hole in
each cycle. Depending on the phase lag the second cavity can effectively absorb
the carriers emitted by the first cavity and nullify the total current or the
set-up can be made to work as a two-particle emitter. We examine the precision
with which the current can be nullified and with which the second cavity
effectively counts the particles emitted by the first one. To achieve
single-particle detection we examine pulsed cavities.
