Silicon photonic chips as quantum-secure hardware fingerprints

Tiny, uncontrollable variations in waveguide geometry that emerge during chip fabrication normally count as defects — here they serve as a unique physical fingerprint. The team built a programmable Mach-Zehnder interferometer mesh in silicon nitride, extracted its characteristic unitary transformation, then designed a quantum readout protocol using single-photon states to probe it. Maximally mixed quantum states prevent an eavesdropper from reconstructing the device's secret signature. Monte Carlo simulations predict equal error rates as low as 10⁻¹⁴, suggesting this approach could underpin hardware authentication robust against both classical and quantum adversaries.