Fig. 1. Quantum optical switch and diode based on chiral quantum coupling. (a) Optical switch based on the coupling between a single atom and a cavity^[46]; (b) directional optical switch enabled by chiral coupling between a single atom and a whispering gallery mode microcavity^[47]; (c) optical diode realized through the coupling of an atomic ensemble with a nanofiber^[42]

Fig. 2. Optical isolation and circulator devices based on chiral cross-Kerr nonlinearity^[38]. (a) Schematic of the experimental setup embedding atoms in a waveguide system. (b) illustration of the N-level atomic structure

Fig. 3. Unidirectional transmission spectra of the probe light field induced by chiral Kerr nonlinear interactions^[39]. (a) Near resonance position; (b) away from the resonance position

Fig. 4. Energy level schematic diagrams of the EIT process and the Raman process^[54]. (a) EIT process; (b) Raman process

Fig. 5. Transmission spectra of a weak probe light field under EIT conditions for forward and backward propagation^［54］. （a） Forward; （b） backward

Fig. 6. Unidirectional transmission spectra of genuine single-photon signals^[54]. (a) Single-photon signals for forward and backward transmission; (b) single-photon wave packets generated by the atomic spontaneous four-wave mixing process

Fig. 7. Unidirectional transmission isolation contrasts of the chiral EIT operating region and the Raman operating region^[54]

Fig. 8. Single-photon diodes implemented by different methods. (a) Single-photon diode realized through chiral Jaynes-Cummings coupling^[44]; (b) directional single-photon emitter and optical circulator enabled by the chiral coupling of quantum dots in a photonic crystal^[48]

Fig. 9. Chiral coupling between a single atom and a whispering gallery mode resonator^[43]

Fig. 10. Experimental results of the optical circulator phase modulation induced by chiral Kerr nonlinearity^[39]. (a)(b)(c) The phase variations in the two arms of the interferometer with respect to the probe light detuning under different frequency detunings of the control light field

Fig. 11. Unidirectional transmission characteristics of the photonic qubits^[75]. (a) Forward transmission spectrum; (b) backward transmission spectrum

Fig. 12. Unidirectional quantum storage of the photonic qubits^[75]. (a) Time-correlated counts of the input signal for photonic qubit storage; (b) time-correlated counts of the stored and retrieved signal for forward transmission; (c) time-correlated counts of the stored and retrieved signal for backward transmission