Few-photon diode in a chiral waveguide modulated by Rydberg atoms

We investigate single- and two-photon transport in a one-dimensional waveguide chirally coupled to dissipative Rydberg atom pairs. Using the Laplace transform method, we analytically solve the single- and two-photon scattering problems. Our results show that, by leveraging dissipative effects and the chiral coupling structure, the system can act as a perfect single-photon diode, i. e., the transmittance is unity from one side and zero from the other. A two-photon diode is also realized. Interestingly, the transmitted probability density of the diode increases significantly when atomic dissipation is included. Notably, in the absence of dissipation, transmission is primarily due to correlated photons, whereas in the dissipative system, it is dominated by freely propagating photons. Furthermore, the Rydberg coupling between the atoms, which is experimentally tunable, can be used to modulate the diode effect. Finally, we find that reducing the width of the incident photon wavepacket further enhances the transmission probability density of the two-photon diode. The proposed scheme has potential for applications in quantum communication.