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We investigate the light propagation dynamics in ultra-cold Rydberg medium with inverted-Y configuration based on the superatom theory. It is viable to store light information in two types of atomic spin coherence (trivial spin coherence and Rydberg spin coherence), which makes the system a prospective platform for versatile light manipulation. A normal feature is to realize efficient light storage with simultaneous resonant control fields applied. An intriguing feature is to split light into two beams with different intensities and statistical properties if the control fields are applied separately. The beam of light retrieved from the Rydberg spin coherence is severely attenuated and shows anti-bunching character accompanied by the cooperative optical nonlinearity. Moreover, generation and manipulation of beating signal are achievable by applying the non-resonant control fields.

We study in theory the single-photon Rydberg excitation in an ensemble of two-level cold atoms at finite low temperatures. Rydberg population plotted against laser detuning may exhibit a nonlinear bistable behavior arising from the dipole–dipole interactions manifested as a van der Waals (vdW) potential. We find that Doppler broadening can result in a remarkable reduction of the bistable region, which may disappear as the atomic temperature increases to a certain value, of the order of tens to hundreds of μK. This special temperature, depending critically on the vdW potential, can be largely raised by partially eliminating the Doppler effect, when a double-photon excitation scheme is used to replace the single-photon excitation scheme.

We propose a feasible and flexible scheme to realize all-optical photon switching, router and amplifier by using a passive-active optomechanical system consisting of a passive cavity, an active cavity and a common movable membrane oscillator. Due to the cooperation between the gain effect of the active cavity and the interference effect between the probe fields, some novel phenomena arise, such as the frequency-independent perfect reflection first proposed in this paper, controllable photon routing, tunable fast and slow lights and so on. Based on the results, a photon switching of absorption-amplification and fast-slow-light transitions, and a photon router with controllable direction and intensity can be realized by adjusting relevant parameters such as the strengths of control fields and the relative phase between probe fields. Such a scheme may provide a promising platform for controllable photon transport and photonic device fabrication.

We investigate the stationary entanglement properties in a hybrid system consisting of an optical cavity, a mechanical resonator, a charged object, and an atomic ensemble. Numerical results show that this hybrid system exhibits three kinds of controllable bipartite entanglements in an experimentally accessible parameter regime with the help of the charged object. More importantly, it is viable to enhance on demand each bipartite entanglement at the expense of reducing others by modulating the Coulomb coupling strength. Last but not least, these bipartite entanglements seem more robust against on the environmental temperature for the positive Coulomb interaction.

We study the steady optical responses of a cold atomic ensemble driven into the three-level ladder configuration involving a Rydberg state at finite temperatures. By improving the superatom model with thermal movement included, we calculate relevant atomic coherence effects and find that the residual Doppler broadening at the mK–K temperatures will weaken the nonclassical properties of transmitted probe photons. Furthermore, propagation directions of the probe and coupling fields have a great influence on various properties related to electromagnetically induced transparency. That is, the residual Doppler effect is more destructive to relevant atomic coherence effects in the co-propagation case but can be partially eliminated in the counter-propagation case.