Structured light in the quantum regime has garnered considerable attention due to the opportunities it offers when mixing light’s internal degrees of freedom, for high-dimensional and multidimensional quantum states of light. A popular example is to harness polarization and spatial entangled photons with a shared topological invariant that is robust against numerous families of noisy quantum channels. Yet, producing such states with high purity and adaptability remains challenging. Here, we introduce a compact, self-locking Mach-Zehnder interferometer that integrates digital spatial light modulators with static beam displacers to map spatial-mode entanglement from a parametric down-conversion source onto topological entanglement with high fidelity. The device also mimics the action of a reprogrammable controlled-unitary gate, digitally driven by the spatial light modulator with the desired target state preparation achieved through postselection. This approach is an enabling platform and provides a practical route to generating reliable, high-purity quantum structured light with topological features, both at the single-photon level and as entangled states, a direction of growing topical interest.

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• Geometric & topological phases
• Optical quantum information processing
• Photon pairs & parametric down-conversion
• Quantum state engineering
• Quantum states of light
• Structured light
• Topological effects in photonic systems
• Spatial light modulators