Qubits and permutation symmetry
In general, a state of $n$ qubits is a state of $n$ distingushable particles. Eg. 
$|01\rangle$ means that the first particle is in the state $|0\rangle$, and the second is in the state $|1\rangle$.

How can be elementary particles distinguishable? Place two particles in different places. Eg. two electrons are in the positions $x_1$ and $x_2$, respectively. (Or two photons in two consecutive pulses, one in each.)

However, you can make the qubits indistinguishable by imposing a permutation symmetry, i.e. symmetrization and antisymmetrization.

And $n$ photons in the same place gives 'automatically' symmetrized state.