  Distinguishing between strings of data or waveforms is at the core of
multiple applications in information technologies. In a quantum language the
task is to design protocols to differentiate quantum states. Quantum-based
technologies promises to go beyond the capabilities offered by technologies
based on classical principles. However the implementation of the logical gates
that are the core of these systems is challenging since they should overcome
quantum decoherence, low probability of success and are prone to errors. One
unexpected contribution of considering ideas in the quantum world is to inspire
similar solutions in the classical world (quantum-inspired technologies),
protocols that aim at mimicking particular features of quantum algorithms. This
is based on features of quantum physics also shared by waves in the classical
world, such it is the case of interference or entanglement between degrees of
freedom of a single particle. Here we demonstrate in a proof-of-concept
experiment a new type of quantum-inspired protocol based on the idea of quantum
fingerprinting (Phys. Rev. Lett. 87, 167902, 2001). Information is encoded on
optical beams with orbital angular momentum (OAM). These beams allow to
implement a crucial element of our system, a new type of Fredkin gate or
polarization-controlled SWAP operation that exchange data between OAM beams.
The protocols can evaluate the similarity between pairs of waveforms and
strings of bits and quarts without unveiling the information content of the
data.
