  The efficient single photon emission capabilities of quantum dot molecules
position them as promising platforms for quantum information processing.
Furthermore, quantum dot molecules feature a "decoherence-free" subspace that
enables spin qubits with long coherence time. To efficiently read out the spin
state within this subspace requires optically cycling isolated transitions that
originate from a triplet manifold within the quantum dot molecule. We propose
and theoretically study a two-stage spin readout protocol within this
decoherence-free subspace that allows single-shot readout performance. The
process incorporates a microwave $\pi$-pulse and optically cycling the isolated
transitions, which induces fluorescence that allows us to identify the initial
spin state. This protocol offers enhanced readout fidelity compared to previous
schemes that rely on the excitation of transitions that strongly decay to
multiple ground states or require long initialization via slow, optically
forbidden transitions. By simulating the performance of the protocol, we show
that an optimal spin readout fidelity of over 97% and single-shot readout
performance are achievable for a photon collection efficiency of just 0.12%.
This high readout performance for such realistic photon collection conditions
within the decoherence-free subspace expands the potential of quantum dot
molecules as building blocks for quantum networks.
