Fig. 1

a Schematic setup of an integrated waveguide trimer simulator of a reduced Born–Markov open quantum system. The different colors in the waveguides represent dynamical (z dependent or time dependent) random changes in the propagation constants, whose effects emulate site-energy fluctuations induced by the environment. Notice the orange and green waveguides represent the strongly coupled sites and the blue waveguide represents the third site that is weakly coupled to the upper sites. b Experimental setup employed to carry out experiments within the two-excitation manifold: a two-photon source at a wavelength of 815 nm was implemented by means of spontaneous parametric down-conversion from a pump laser at a wavelength of 407.5 nm. Photons emerging at the output of the device are collected via a fiber array and subsequently fed into avalanche photodiodes (APDs). In the absence of noise all waveguides have the same propagation constants. Consequently, exciting one of the uppers sites with laser light (λ = 633 nm) creates the intensity dynamics shown in d. We observe that light propagates through the system hopping predominantly among the upper waveguides, i.e., the strongly coupled sites. In the presence of dephasing f, we observe the emergence of a uniform redistribution of energy among all the waveguides. Notice in c–f the green curve represents the intensity along the excited waveguide, the orange curve describes the intensity along the second upper site and the blue one is the intensity recorded from the lower site, see a. These experiments unequivocally demonstrate that within the single-excitation manifold dephasing induces a uniform redistribution of energy and as a result the farthest waveguide becomes populated with about 1/3 of the total energy. c, e depict the theoretically calculated single-excitation dynamics in a noiseless and a dephasing trimer, respectively