Single-particle entanglement

I give a simple argument that demonstrates that the state $\mid 0⟩\mid 1⟩+\mid 1⟩\mid 0⟩$, with $\mid 0⟩$ denoting a state with 0 particles (or photons) and $\mid 1⟩$ a one-particle state, is entangled in spite of recent claims to the contrary. I also discuss viewpoints on the old controversy about whether the above state can be said to display single-particle or single-photon nonlocality.