Fig. 1. Simplified sketch of the experimental design.

The input quantum state |ψ〉 is imprinted on a single photon using an SLM-A. The single photon is subsequently sent to the cloning machine for optimal cloning. The cloning machine consists of a delay line (DL), to adjust the arrival time of the input photon, a second photon that is in a completely mixed state when exiting SLM-B, and a first beam splitter (BS1). The two photons are made to arrive at the beam splitter simultaneously using the DL. The two photons exiting one of the output ports of the first beam splitter together are separated at a second beam splitter (BS2) and are sent out of the cloning machine. The cloned photons are then detected and characterized using detectors (D1 and D2) and SLMs (SLM-C and SLM-D), respectively. (A to C) Examples of Hong-Ou-Mandel (HOM) coalescence curves for input photons of $\mathrm{\ell }=-1,0,1,$ respectively (top to bottom). The curve is obtained by recording the coincidences between the output ports of BS2 for various delays of one of the input photons. Examples of enhancement peaks of ${\mathit{R}}_{\mathrm{\ell }=-1}=1.97\pm 0.08$, ${\mathit{R}}_{\mathrm{\ell }=0}=2.02\pm 0.08$, and ${\mathit{R}}_{\mathrm{\ell }=1}=1.99\pm 0.09$ are obtained experimentally, and agree with the theoretical value of R_th = 2, corresponding to a visibility of $\mathcal{V}=1$.