High-contrast transparency comb of the electromagnetically-induced-transparency memory

Quantum interface of coherent optical field and atomic excitations plays an important role in quantum metrology and quantum information science. The electromagnetically-induced-transparency (EIT) technique has shown versatile and powerful capability in many applications during the last decades. By using efficient EIT-based memory, we directly observed single-photon-level Ramsey interference and also high-contrast spectral transparency comb with a visibility up to about 0.81 at around the resonant line in cold atoms. The interference fringes are mainly influenced by the pulse repetition period, the waveform overlap of the slowed and retrieved signal pulses, and the coherent lifetime of the EIT memory. All these factors have been investigated in detail. Such high-contrast interference fringe may offer us methods for precision measurement and potential applications in areas of atomic clock and magnetometry.