Optical simulation of the quantum Hadamard operator

A possible way to optically simulate quantum algorithms is by making use of the spatial distribution of light in a laser beam. In this approach, the quantum states are represented by the amplitudes of the electromagnetic field in the beam. Temporal evolution is simulated by using optical elements such as lenses and phase shifters. Different elements are required depending on the operation whose implementation is desired. In this paper, we present an optical module to simulate the Hadamard transformation operating on a single qubit. The system is composed by a set of lenses, a phase plate and a phase grating and it could be used as a part of more complex arrangements. As an example, we make use of our Hadamard optical module as a part of the quantum circuit that solves the Deutsch problem. We show the obtained experimental results and we discuss the limitations of the proposal.