Fig. 4: Implementation of the multi-particle ‘which-path’ scheme using waveguide-QED with quantum emitters such as atoms in a Λ configuration.

One of the electronic transitions couples to the driving laser (a). The two ground states represent the two “paths'', \(\left\vert 0\right\rangle\) and \(\left\vert 1\right\rangle\). Coherent control pulses act as Hadamard gates (b). Weak illumination pulses couple each emitter in the correct state to the waveguide, creating a conditional displacement (c).