NCTS (South)


DATE2011-05-02

TIME12:00

PLACER49223, Second Physics Building , NCKU

FIELDQuantum Information Science

SPEAKER Dr. Hsiang-Hua Jen(任祥華) - 清華大學物理系

TITLEEfficiency of light-frequency conversion in an atomic ensemble

ABSTRACTIn this talk, we investigate the quantum mechanical interaction of light with matter in the form of a gas of cold atoms: the atomic ensemble. We present a theoretical analysis that involves the interaction of quantized electromagnetic fields (called signal and idler) with the atomic ensemble, and we focus on the photon frequency conversion in an atomic diamond configuration. The motivation of the study comes from potential applications in long-distance quantum communication where it is desirable to generate quantum correlations between telecommunication wavelength light fields and ground level atomic coherences. In the system of interest, the light field produced in the upper arm of an atomic Rb level scheme is chosen to lie in the telecom window. The other field, resonant on a ground level transition, is in the near-infrared region of the spectrum. Telecom light is useful as it minimizes losses in the optical fiber transmission links of any two long-distance quantum communication device. We provide a quantum theory of near-infrared to telecom wavelength conversion in the diamond configuration. The system provides a crucial part of a quantum-repeater memory element, which enables a "stored" near-infrared photon to be converted to a telecom wavelength for transmission without the destruction of light-atom quantum correlation. We calculate the theoretical conversion efficiency, analyzing the role of optical depth of the ensemble, pulse length, and quantum fluctuations on the process.