  If a single-mode nonclassical light is combined with the vacuum on a beam
splitter, then the output state is entangled. As proposed in [Phys. Rev. Lett.
94, 173602 (2005)], by measuring the output-state entanglement for a balanced
lossless beam splitter, one can quantify the input-state nonclassicality. These
measures of nonclassicality (referred to as entanglement potentials) can be
based, in principle, on various entanglement measures, leading to the
negativity (NP) and concurrence (CP) potentials, and the potential for the
relative entropy of entanglement (REEP). We search for the maximal
nonclassicality, which can be achieved by comparing two entanglement measures
for arbitrary two-qubit states and those which can be generated from a
photon-number qubit via a balanced lossless beam-splitter, where the qubit
basis states are the vacuum and single-photon states. Surprisingly, we find
that the maximal nonclassicality, measured by the REEP for a given value of the
NP, can be increased (if NP<0.527) by using either a tunable beam splitter or
by amplitude damping of the output state of the balanced beam splitter. We also
show that the maximal nonclassicality, measured by the NP for a given value of
the REEP, can be increased by dephasing. The entanglement itself is not
increased by these local losses, but the possible ratios of different measures
are affected. Moreover, we show that partially-mixed states can be more
nonclassical than both pure states and completely-mixed states, by comparing
the NP for a given value of the REEP. This implies that not all entanglement
measures can be used as entanglement potentials. Alternatively, a single
balanced lossless beam splitter is not always transferring the whole
nonclassicality of its input state into the entanglement of its output modes.
Applying a lossy beam splitter can solve this problem at least for the cases
analyzed in this paper.
