  A recent paper [Chuan Wang, Phys. Rev. A \textbf{86}, 012323 (2012)]
discussed an entanglement concentration protocol (ECP) for partially entangled
electrons using a quantum dot and microcavity coupled system. In his paper,
each two-electron spin system in a partially entangled state can be
concentrated with the assistance of an ancillary quantum dot and a single
photon. In this paper, we will present an optimal ECP for such entangled
electrons with the help of only one single photon. Compared with the protocol
of Wang, the most significant advantage is that during the whole ECP, the
single photon only needs to pass through one microcavity which will increase
the total success probability if the cavity is imperfect. The whole protocol
can be repeated to get a higher success probability. With the feasible
technology, this protocol may be useful in current long-distance quantum
communications.
