Figure 1

Different 1D scattering setups. (a) The original arrangement [10] uses a three-level emitter, with levels $|g⟩$ and $|e⟩$ coupled via the waveguide, and a third metastable level $|s⟩$ coupled to $|e⟩$ only via classical fields. In an ideal situation, an incident photon (black, the upper left wave packet) is fully reflected (green, the lower left wave packet), for $|g⟩$, or goes freely through (blue, the upper right wave packet), for decoupled state $|s⟩$. In a faulty scattering, though, there is a transmitted component (red, the lower right wave packet) even for $|g⟩$. (b) In the present setup, the scatterer has twofold degenerate ground and excited states $|g_{\pm }⟩$ and $|e_{\pm }⟩$, respectively, coupled by parallel transitions through orthogonally polarized waveguide photons. Even for imperfect scattering processes, if the photon is output with the correct polarization, a high-fidelity phase gate is successfully applied on the emitter. A detection of an incorrectly polarized output, on the other hand, heralds a failure. A $50/50$ beam splitter (BS) and two mirrors ($M1$ and $M2$) maximize the probability of success (see text).Reuse & Permissions

Figure 2

Interferometric setup for polarization flying qubits. Only component $|1{⟩}_p$ interacts with the scatterer. For successful interactions, $|1{⟩}_p$ is reflected up the interferometer by PBS2 and joins $|0{⟩}_p$ at PBS3. At the output, the maximally entangling gate (6) between the flying and the stationary qubits is implemented. For unsuccessful interactions, $|1{⟩}_p$ comes back out through PBS2 and PBS1, which heralds a gate failure. Legends: $\mathrm{PBS}=\mathrm{\text{polarizing beam splitter}}$; $\mathrm{HWP}=\mathrm{\text{half-waveplate}}$; $\mathrm{WFC}=\mathrm{\text{waveform}}$ corrector. See text.Reuse & Permissions