  We compare the standard 50%-efficient single beam splitter method for
Bell-state measurement to a proposed 75%-efficient auxiliary-photon-enhanced
scheme [W. P. Grice, Phys. Rev. A 84, 042331 (2011)] in light of realistic
conditions. The two schemes are compared with consideration for high input
state photon loss, auxiliary state photon loss, detector inefficiency and
coupling loss, detector dark counts, and non-number-resolving detectors. We
also analyze the two schemes when multiplexed arrays of non-number-resolving
detectors are used. Furthermore, we explore the possibility of utilizing
spontaneous parametric down-conversion as the auxiliary photon pair source
required by the enhanced scheme. In these different cases, we determine the
bounds on the detector parameters at which the enhanced scheme becomes superior
to the standard scheme and describe the impact of the different imperfections
on measurement success rate and discrimination fidelity. This is done using a
combination of numeric and analytic techniques. For many of the cases
discussed, the size of the Hilbert space and the number of measurement outcomes
can be very large, which makes direct numerical solutions computationally
costly. To alleviate this problem, all of our numerical computations are
performed using pure states. This requires tracking the loss modes until
measurement and treating dark counts as variations on measurement outcomes
rather than modifications to the state itself. In addition, we provide
approximate analytic expressions that illustrate the effect of different
imperfections on the Bell-state analyzer quality.
