Chengjie Zhu

Fast, high-fidelity, all-optical and dynamically-controlled polarization gate using room-temperature atomic vapor

We demonstrate a fast, all-optical polarization gate in a room-temperature atomic medium. Using a Polarization-Selective-Kerr-Phase-Shift (PSKPS) technique, we selectively write a π phase shift to one circularly-polarized component of a linearly-polarized input signal field. The output signal field maintains its original strength but acquires a 90° linear polarization rotation, demonstrating fast, high-fidelity, dynamically-controlled polarization gate operation. The intensity of the polarization-switching field used in this PKSPK-based polarization gate operation is only 2 mW/cm2, which would be equivalent to 0.5 nW of light power (λ = 800 nm) confined in a typical commercial photonic hollow-core fiber. This development opens a realm of possibilities for potential future extremely low light level telecommunication and information processing systems.

Highly efficient counter-propagation-beams narrow-band ultraviolet frequency conversion in a quantum gas.

We show that highly efficient ultraviolet frequency up conversion can be established in a single-component quantum gas in the counter-propagating weak pump beam geometry where no frequency up conversion can occur in a normal gas. We also show that all light-wave mixing and scattering processes in quantum gases originating from elementary excitations characterized by efficient collective atomic recoil motion are stimulated Raman/hyper-Raman in nature.

Light-wave mixing and scattering with quantum gases

We show that optical processes originating from elementary excitations with dominant collective atomic recoil motion in a quantum gas can profoundly change many nonlinear optical processes routinely observed in a normal gas. Not only multi-photon wave mixing processes all become stimulated Raman or hyper-Raman in nature but the usual forward wave-mixing process, which is the most efficient process in normal gases, is strongly reduced by the condensate structure factor. On the other hand, in the backward direction the Bogoliubov dispersion automatically compensates the optical- wave phase mismatch, resulting in efficient backward light field generation that usually is not supported in normal gases.