Unidirectional and controllable higher-order diffraction by a Rydberg electromagnetically induced grating

A method for diffracting the weak probe beam into unidirectional and higher-order directions is proposed via a Rydberg electromagnetically induced grating, providing a way for the implementations of quantum devices with cold Rydberg atoms. The proposed scheme utilizes a suitable position-dependent adjustment to the two-photon detuning besides the modulation of the standing-wave coupling field, producing an in-phase modulation which can change the parity of the dispersion. We observe that when the modulation amplitude is appropriate, a perfect unidirectional diffraction grating can be realized. In addition, due to the mutual effect between the van der Waals (vdW) interaction and the atom-field interaction length that deeply improves the dispersion of the medium, the probe energy can be counterintuitively transferred into higher-order diffractions as increasing the vdW interaction, leading to the realization of a controllable higher-order diffraction grating via a strong blockade.