Fig. 2.

Experimental setup. (a) Single programmable unit consisting of a Mach-Zehnder interferometer (MZI) equipped with two fully tuneable phase shifters, one internal allowing for a scan of the output distribution over θ ∈ [0, 2π], and one external dictating the relative phase ϕ ∈ [0, 2π] between the two output modes. This makes the MZI act as a fully tuneable beam splitter and allows for coherent implementation of sequences of quantum gates. (b) Image of a single MZI in the processor. The third phase shifter in the bottom arm of the interferometer is not used. (c) Overview of the setup. A single-photon source generates single-photon pairs at telecom wavelength. One photon is sent to a single-photon detector D0, while the other one is coupled into the processor and undergoes the desired computation. It is then detected, in coincidence with the photon in D0, either in detector D1 or in D2/D3 after the agent plays the classical/quantum strategy (see Fig. 3 for more details). The coincidence events are recorded with a custom-made time tagging module (TTM). Different areas of the processor are assigned to either the agent or the environment, that can perform a Grover-like quantum search to look for rewarded action sequences in quantum epochs. The agent has access to a classical control that updates its policy.