  Cooper pair splitters hold utility as a platform for investigating the
entanglement of electrons in Cooper pairs, but probing splitters with
voltage-biased Ohmic contacts prevents the retention of electrons from split
pairs since they can escape to the drain reservoirs. We report the ability to
controllably split and retain single Cooper pairs in a multi-quantum-dot device
isolated from lead reservoirs, and separately demonstrate a technique for
detecting the electrons emerging from a split pair. First, we identify a
coherent Cooper pair splitting charge transition using dispersive gate sensing
at GHz frequencies. Second, we utilize a double quantum dot as an electron
parity sensor to detect parity changes resulting from electrons emerging from a
superconducting island.
